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janus/lib/python3.10/site-packages/networkx/algorithms/flow/__init__.py

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+from .maxflow import *
+from .mincost import *
+from .boykovkolmogorov import *
+from .dinitz_alg import *
+from .edmondskarp import *
+from .gomory_hu import *
+from .preflowpush import *
+from .shortestaugmentingpath import *
+from .capacityscaling import *
+from .networksimplex import *
+from .utils import build_flow_dict, build_residual_network

janus/lib/python3.10/site-packages/networkx/algorithms/flow/boykovkolmogorov.py

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+"""
+Boykov-Kolmogorov algorithm for maximum flow problems.
+"""
+
+from collections import deque
+from operator import itemgetter
+
+import networkx as nx
+from networkx.algorithms.flow.utils import build_residual_network
+
+__all__ = ["boykov_kolmogorov"]
+
+
+@nx._dispatchable(edge_attrs={"capacity": float("inf")}, returns_graph=True)
+def boykov_kolmogorov(
+    G, s, t, capacity="capacity", residual=None, value_only=False, cutoff=None
+):
+    r"""Find a maximum single-commodity flow using Boykov-Kolmogorov algorithm.
+
+    This function returns the residual network resulting after computing
+    the maximum flow. See below for details about the conventions
+    NetworkX uses for defining residual networks.
+
+    This algorithm has worse case complexity $O(n^2 m |C|)$ for $n$ nodes, $m$
+    edges, and $|C|$ the cost of the minimum cut [1]_. This implementation
+    uses the marking heuristic defined in [2]_ which improves its running
+    time in many practical problems.
+
+    Parameters
+    ----------
+    G : NetworkX graph
+        Edges of the graph are expected to have an attribute called
+        'capacity'. If this attribute is not present, the edge is
+        considered to have infinite capacity.
+
+    s : node
+        Source node for the flow.
+
+    t : node
+        Sink node for the flow.
+
+    capacity : string
+        Edges of the graph G are expected to have an attribute capacity
+        that indicates how much flow the edge can support. If this
+        attribute is not present, the edge is considered to have
+        infinite capacity. Default value: 'capacity'.
+
+    residual : NetworkX graph
+        Residual network on which the algorithm is to be executed. If None, a
+        new residual network is created. Default value: None.
+
+    value_only : bool
+        If True compute only the value of the maximum flow. This parameter
+        will be ignored by this algorithm because it is not applicable.
+
+    cutoff : integer, float
+        If specified, the algorithm will terminate when the flow value reaches
+        or exceeds the cutoff. In this case, it may be unable to immediately
+        determine a minimum cut. Default value: None.
+
+    Returns
+    -------
+    R : NetworkX DiGraph
+        Residual network after computing the maximum flow.
+
+    Raises
+    ------
+    NetworkXError
+        The algorithm does not support MultiGraph and MultiDiGraph. If
+        the input graph is an instance of one of these two classes, a
+        NetworkXError is raised.
+
+    NetworkXUnbounded
+        If the graph has a path of infinite capacity, the value of a
+        feasible flow on the graph is unbounded above and the function
+        raises a NetworkXUnbounded.
+
+    See also
+    --------
+    :meth:`maximum_flow`
+    :meth:`minimum_cut`
+    :meth:`preflow_push`
+    :meth:`shortest_augmenting_path`
+
+    Notes
+    -----
+    The residual network :samp:`R` from an input graph :samp:`G` has the
+    same nodes as :samp:`G`. :samp:`R` is a DiGraph that contains a pair
+    of edges :samp:`(u, v)` and :samp:`(v, u)` iff :samp:`(u, v)` is not a
+    self-loop, and at least one of :samp:`(u, v)` and :samp:`(v, u)` exists
+    in :samp:`G`.
+
+    For each edge :samp:`(u, v)` in :samp:`R`, :samp:`R[u][v]['capacity']`
+    is equal to the capacity of :samp:`(u, v)` in :samp:`G` if it exists
+    in :samp:`G` or zero otherwise. If the capacity is infinite,
+    :samp:`R[u][v]['capacity']` will have a high arbitrary finite value
+    that does not affect the solution of the problem. This value is stored in
+    :samp:`R.graph['inf']`. For each edge :samp:`(u, v)` in :samp:`R`,
+    :samp:`R[u][v]['flow']` represents the flow function of :samp:`(u, v)` and
+    satisfies :samp:`R[u][v]['flow'] == -R[v][u]['flow']`.
+
+    The flow value, defined as the total flow into :samp:`t`, the sink, is
+    stored in :samp:`R.graph['flow_value']`. If :samp:`cutoff` is not
+    specified, reachability to :samp:`t` using only edges :samp:`(u, v)` such
+    that :samp:`R[u][v]['flow'] < R[u][v]['capacity']` induces a minimum
+    :samp:`s`-:samp:`t` cut.
+
+    Examples
+    --------
+    >>> from networkx.algorithms.flow import boykov_kolmogorov
+
+    The functions that implement flow algorithms and output a residual
+    network, such as this one, are not imported to the base NetworkX
+    namespace, so you have to explicitly import them from the flow package.
+
+    >>> G = nx.DiGraph()
+    >>> G.add_edge("x", "a", capacity=3.0)
+    >>> G.add_edge("x", "b", capacity=1.0)
+    >>> G.add_edge("a", "c", capacity=3.0)
+    >>> G.add_edge("b", "c", capacity=5.0)
+    >>> G.add_edge("b", "d", capacity=4.0)
+    >>> G.add_edge("d", "e", capacity=2.0)
+    >>> G.add_edge("c", "y", capacity=2.0)
+    >>> G.add_edge("e", "y", capacity=3.0)
+    >>> R = boykov_kolmogorov(G, "x", "y")
+    >>> flow_value = nx.maximum_flow_value(G, "x", "y")
+    >>> flow_value
+    3.0
+    >>> flow_value == R.graph["flow_value"]
+    True
+
+    A nice feature of the Boykov-Kolmogorov algorithm is that a partition
+    of the nodes that defines a minimum cut can be easily computed based
+    on the search trees used during the algorithm. These trees are stored
+    in the graph attribute `trees` of the residual network.
+
+    >>> source_tree, target_tree = R.graph["trees"]
+    >>> partition = (set(source_tree), set(G) - set(source_tree))
+
+    Or equivalently:
+
+    >>> partition = (set(G) - set(target_tree), set(target_tree))
+
+    References
+    ----------
+    .. [1] Boykov, Y., & Kolmogorov, V. (2004). An experimental comparison
+           of min-cut/max-flow algorithms for energy minimization in vision.
+           Pattern Analysis and Machine Intelligence, IEEE Transactions on,
+           26(9), 1124-1137.
+           https://doi.org/10.1109/TPAMI.2004.60
+
+    .. [2] Vladimir Kolmogorov. Graph-based Algorithms for Multi-camera
+           Reconstruction Problem. PhD thesis, Cornell University, CS Department,
+           2003. pp. 109-114.
+           https://web.archive.org/web/20170809091249/https://pub.ist.ac.at/~vnk/papers/thesis.pdf
+
+    """
+    R = boykov_kolmogorov_impl(G, s, t, capacity, residual, cutoff)
+    R.graph["algorithm"] = "boykov_kolmogorov"
+    nx._clear_cache(R)
+    return R
+
+
+def boykov_kolmogorov_impl(G, s, t, capacity, residual, cutoff):
+    if s not in G:
+        raise nx.NetworkXError(f"node {str(s)} not in graph")
+    if t not in G:
+        raise nx.NetworkXError(f"node {str(t)} not in graph")
+    if s == t:
+        raise nx.NetworkXError("source and sink are the same node")
+
+    if residual is None:
+        R = build_residual_network(G, capacity)
+    else:
+        R = residual
+
+    # Initialize/reset the residual network.
+    # This is way too slow
+    # nx.set_edge_attributes(R, 0, 'flow')
+    for u in R:
+        for e in R[u].values():
+            e["flow"] = 0
+
+    # Use an arbitrary high value as infinite. It is computed
+    # when building the residual network.
+    INF = R.graph["inf"]
+
+    if cutoff is None:
+        cutoff = INF
+
+    R_succ = R.succ
+    R_pred = R.pred
+
+    def grow():
+        """Bidirectional breadth-first search for the growth stage.
+
+        Returns a connecting edge, that is and edge that connects
+        a node from the source search tree with a node from the
+        target search tree.
+        The first node in the connecting edge is always from the
+        source tree and the last node from the target tree.
+        """
+        while active:
+            u = active[0]
+            if u in source_tree:
+                this_tree = source_tree
+                other_tree = target_tree
+                neighbors = R_succ
+            else:
+                this_tree = target_tree
+                other_tree = source_tree
+                neighbors = R_pred
+            for v, attr in neighbors[u].items():
+                if attr["capacity"] - attr["flow"] > 0:
+                    if v not in this_tree:
+                        if v in other_tree:
+                            return (u, v) if this_tree is source_tree else (v, u)
+                        this_tree[v] = u
+                        dist[v] = dist[u] + 1
+                        timestamp[v] = timestamp[u]
+                        active.append(v)
+                    elif v in this_tree and _is_closer(u, v):
+                        this_tree[v] = u
+                        dist[v] = dist[u] + 1
+                        timestamp[v] = timestamp[u]
+            _ = active.popleft()
+        return None, None
+
+    def augment(u, v):
+        """Augmentation stage.
+
+        Reconstruct path and determine its residual capacity.
+        We start from a connecting edge, which links a node
+        from the source tree to a node from the target tree.
+        The connecting edge is the output of the grow function
+        and the input of this function.
+        """
+        attr = R_succ[u][v]
+        flow = min(INF, attr["capacity"] - attr["flow"])
+        path = [u]
+        # Trace a path from u to s in source_tree.
+        w = u
+        while w != s:
+            n = w
+            w = source_tree[n]
+            attr = R_pred[n][w]
+            flow = min(flow, attr["capacity"] - attr["flow"])
+            path.append(w)
+        path.reverse()
+        # Trace a path from v to t in target_tree.
+        path.append(v)
+        w = v
+        while w != t:
+            n = w
+            w = target_tree[n]
+            attr = R_succ[n][w]
+            flow = min(flow, attr["capacity"] - attr["flow"])
+            path.append(w)
+        # Augment flow along the path and check for saturated edges.
+        it = iter(path)
+        u = next(it)
+        these_orphans = []
+        for v in it:
+            R_succ[u][v]["flow"] += flow
+            R_succ[v][u]["flow"] -= flow
+            if R_succ[u][v]["flow"] == R_succ[u][v]["capacity"]:
+                if v in source_tree:
+                    source_tree[v] = None
+                    these_orphans.append(v)
+                if u in target_tree:
+                    target_tree[u] = None
+                    these_orphans.append(u)
+            u = v
+        orphans.extend(sorted(these_orphans, key=dist.get))
+        return flow
+
+    def adopt():
+        """Adoption stage.
+
+        Reconstruct search trees by adopting or discarding orphans.
+        During augmentation stage some edges got saturated and thus
+        the source and target search trees broke down to forests, with
+        orphans as roots of some of its trees. We have to reconstruct
+        the search trees rooted to source and target before we can grow
+        them again.
+        """
+        while orphans:
+            u = orphans.popleft()
+            if u in source_tree:
+                tree = source_tree
+                neighbors = R_pred
+            else:
+                tree = target_tree
+                neighbors = R_succ
+            nbrs = ((n, attr, dist[n]) for n, attr in neighbors[u].items() if n in tree)
+            for v, attr, d in sorted(nbrs, key=itemgetter(2)):
+                if attr["capacity"] - attr["flow"] > 0:
+                    if _has_valid_root(v, tree):
+                        tree[u] = v
+                        dist[u] = dist[v] + 1
+                        timestamp[u] = time
+                        break
+            else:
+                nbrs = (
+                    (n, attr, dist[n]) for n, attr in neighbors[u].items() if n in tree
+                )
+                for v, attr, d in sorted(nbrs, key=itemgetter(2)):
+                    if attr["capacity"] - attr["flow"] > 0:
+                        if v not in active:
+                            active.append(v)
+                    if tree[v] == u:
+                        tree[v] = None
+                        orphans.appendleft(v)
+                if u in active:
+                    active.remove(u)
+                del tree[u]
+
+    def _has_valid_root(n, tree):
+        path = []
+        v = n
+        while v is not None:
+            path.append(v)
+            if v in (s, t):
+                base_dist = 0
+                break
+            elif timestamp[v] == time:
+                base_dist = dist[v]
+                break
+            v = tree[v]
+        else:
+            return False
+        length = len(path)
+        for i, u in enumerate(path, 1):
+            dist[u] = base_dist + length - i
+            timestamp[u] = time
+        return True
+
+    def _is_closer(u, v):
+        return timestamp[v] <= timestamp[u] and dist[v] > dist[u] + 1
+
+    source_tree = {s: None}
+    target_tree = {t: None}
+    active = deque([s, t])
+    orphans = deque()
+    flow_value = 0
+    # data structures for the marking heuristic
+    time = 1
+    timestamp = {s: time, t: time}
+    dist = {s: 0, t: 0}
+    while flow_value < cutoff:
+        # Growth stage
+        u, v = grow()
+        if u is None:
+            break
+        time += 1
+        # Augmentation stage
+        flow_value += augment(u, v)
+        # Adoption stage
+        adopt()
+
+    if flow_value * 2 > INF:
+        raise nx.NetworkXUnbounded("Infinite capacity path, flow unbounded above.")
+
+    # Add source and target tree in a graph attribute.
+    # A partition that defines a minimum cut can be directly
+    # computed from the search trees as explained in the docstrings.
+    R.graph["trees"] = (source_tree, target_tree)
+    # Add the standard flow_value graph attribute.
+    R.graph["flow_value"] = flow_value
+    return R

janus/lib/python3.10/site-packages/networkx/algorithms/flow/capacityscaling.py

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+"""
+Capacity scaling minimum cost flow algorithm.
+"""
+
+__all__ = ["capacity_scaling"]
+
+from itertools import chain
+from math import log
+
+import networkx as nx
+
+from ...utils import BinaryHeap, arbitrary_element, not_implemented_for
+
+
+def _detect_unboundedness(R):
+    """Detect infinite-capacity negative cycles."""
+    G = nx.DiGraph()
+    G.add_nodes_from(R)
+
+    # Value simulating infinity.
+    inf = R.graph["inf"]
+    # True infinity.
+    f_inf = float("inf")
+    for u in R:
+        for v, e in R[u].items():
+            # Compute the minimum weight of infinite-capacity (u, v) edges.
+            w = f_inf
+            for k, e in e.items():
+                if e["capacity"] == inf:
+                    w = min(w, e["weight"])
+            if w != f_inf:
+                G.add_edge(u, v, weight=w)
+
+    if nx.negative_edge_cycle(G):
+        raise nx.NetworkXUnbounded(
+            "Negative cost cycle of infinite capacity found. "
+            "Min cost flow may be unbounded below."
+        )
+
+
+@not_implemented_for("undirected")
+def _build_residual_network(G, demand, capacity, weight):
+    """Build a residual network and initialize a zero flow."""
+    if sum(G.nodes[u].get(demand, 0) for u in G) != 0:
+        raise nx.NetworkXUnfeasible("Sum of the demands should be 0.")
+
+    R = nx.MultiDiGraph()
+    R.add_nodes_from(
+        (u, {"excess": -G.nodes[u].get(demand, 0), "potential": 0}) for u in G
+    )
+
+    inf = float("inf")
+    # Detect selfloops with infinite capacities and negative weights.
+    for u, v, e in nx.selfloop_edges(G, data=True):
+        if e.get(weight, 0) < 0 and e.get(capacity, inf) == inf:
+            raise nx.NetworkXUnbounded(
+                "Negative cost cycle of infinite capacity found. "
+                "Min cost flow may be unbounded below."
+            )
+
+    # Extract edges with positive capacities. Self loops excluded.
+    if G.is_multigraph():
+        edge_list = [
+            (u, v, k, e)
+            for u, v, k, e in G.edges(data=True, keys=True)
+            if u != v and e.get(capacity, inf) > 0
+        ]
+    else:
+        edge_list = [
+            (u, v, 0, e)
+            for u, v, e in G.edges(data=True)
+            if u != v and e.get(capacity, inf) > 0
+        ]
+    # Simulate infinity with the larger of the sum of absolute node imbalances
+    # the sum of finite edge capacities or any positive value if both sums are
+    # zero. This allows the infinite-capacity edges to be distinguished for
+    # unboundedness detection and directly participate in residual capacity
+    # calculation.
+    inf = (
+        max(
+            sum(abs(R.nodes[u]["excess"]) for u in R),
+            2
+            * sum(
+                e[capacity]
+                for u, v, k, e in edge_list
+                if capacity in e and e[capacity] != inf
+            ),
+        )
+        or 1
+    )
+    for u, v, k, e in edge_list:
+        r = min(e.get(capacity, inf), inf)
+        w = e.get(weight, 0)
+        # Add both (u, v) and (v, u) into the residual network marked with the
+        # original key. (key[1] == True) indicates the (u, v) is in the
+        # original network.
+        R.add_edge(u, v, key=(k, True), capacity=r, weight=w, flow=0)
+        R.add_edge(v, u, key=(k, False), capacity=0, weight=-w, flow=0)
+
+    # Record the value simulating infinity.
+    R.graph["inf"] = inf
+
+    _detect_unboundedness(R)
+
+    return R
+
+
+def _build_flow_dict(G, R, capacity, weight):
+    """Build a flow dictionary from a residual network."""
+    inf = float("inf")
+    flow_dict = {}
+    if G.is_multigraph():
+        for u in G:
+            flow_dict[u] = {}
+            for v, es in G[u].items():
+                flow_dict[u][v] = {
+                    # Always saturate negative selfloops.
+                    k: (
+                        0
+                        if (
+                            u != v or e.get(capacity, inf) <= 0 or e.get(weight, 0) >= 0
+                        )
+                        else e[capacity]
+                    )
+                    for k, e in es.items()
+                }
+            for v, es in R[u].items():
+                if v in flow_dict[u]:
+                    flow_dict[u][v].update(
+                        (k[0], e["flow"]) for k, e in es.items() if e["flow"] > 0
+                    )
+    else:
+        for u in G:
+            flow_dict[u] = {
+                # Always saturate negative selfloops.
+                v: (
+                    0
+                    if (u != v or e.get(capacity, inf) <= 0 or e.get(weight, 0) >= 0)
+                    else e[capacity]
+                )
+                for v, e in G[u].items()
+            }
+            flow_dict[u].update(
+                (v, e["flow"])
+                for v, es in R[u].items()
+                for e in es.values()
+                if e["flow"] > 0
+            )
+    return flow_dict
+
+
+@nx._dispatchable(
+    node_attrs="demand", edge_attrs={"capacity": float("inf"), "weight": 0}
+)
+def capacity_scaling(
+    G, demand="demand", capacity="capacity", weight="weight", heap=BinaryHeap
+):
+    r"""Find a minimum cost flow satisfying all demands in digraph G.
+
+    This is a capacity scaling successive shortest augmenting path algorithm.
+
+    G is a digraph with edge costs and capacities and in which nodes
+    have demand, i.e., they want to send or receive some amount of
+    flow. A negative demand means that the node wants to send flow, a
+    positive demand means that the node want to receive flow. A flow on
+    the digraph G satisfies all demand if the net flow into each node
+    is equal to the demand of that node.
+
+    Parameters
+    ----------
+    G : NetworkX graph
+        DiGraph or MultiDiGraph on which a minimum cost flow satisfying all
+        demands is to be found.
+
+    demand : string
+        Nodes of the graph G are expected to have an attribute demand
+        that indicates how much flow a node wants to send (negative
+        demand) or receive (positive demand). Note that the sum of the
+        demands should be 0 otherwise the problem in not feasible. If
+        this attribute is not present, a node is considered to have 0
+        demand. Default value: 'demand'.
+
+    capacity : string
+        Edges of the graph G are expected to have an attribute capacity
+        that indicates how much flow the edge can support. If this
+        attribute is not present, the edge is considered to have
+        infinite capacity. Default value: 'capacity'.
+
+    weight : string
+        Edges of the graph G are expected to have an attribute weight
+        that indicates the cost incurred by sending one unit of flow on
+        that edge. If not present, the weight is considered to be 0.
+        Default value: 'weight'.
+
+    heap : class
+        Type of heap to be used in the algorithm. It should be a subclass of
+        :class:`MinHeap` or implement a compatible interface.
+
+        If a stock heap implementation is to be used, :class:`BinaryHeap` is
+        recommended over :class:`PairingHeap` for Python implementations without
+        optimized attribute accesses (e.g., CPython) despite a slower
+        asymptotic running time. For Python implementations with optimized
+        attribute accesses (e.g., PyPy), :class:`PairingHeap` provides better
+        performance. Default value: :class:`BinaryHeap`.
+
+    Returns
+    -------
+    flowCost : integer
+        Cost of a minimum cost flow satisfying all demands.
+
+    flowDict : dictionary
+        If G is a digraph, a dict-of-dicts keyed by nodes such that
+        flowDict[u][v] is the flow on edge (u, v).
+        If G is a MultiDiGraph, a dict-of-dicts-of-dicts keyed by nodes
+        so that flowDict[u][v][key] is the flow on edge (u, v, key).
+
+    Raises
+    ------
+    NetworkXError
+        This exception is raised if the input graph is not directed,
+        not connected.
+
+    NetworkXUnfeasible
+        This exception is raised in the following situations:
+
+            * The sum of the demands is not zero. Then, there is no
+              flow satisfying all demands.
+            * There is no flow satisfying all demand.
+
+    NetworkXUnbounded
+        This exception is raised if the digraph G has a cycle of
+        negative cost and infinite capacity. Then, the cost of a flow
+        satisfying all demands is unbounded below.
+
+    Notes
+    -----
+    This algorithm does not work if edge weights are floating-point numbers.
+
+    See also
+    --------
+    :meth:`network_simplex`
+
+    Examples
+    --------
+    A simple example of a min cost flow problem.
+
+    >>> G = nx.DiGraph()
+    >>> G.add_node("a", demand=-5)
+    >>> G.add_node("d", demand=5)
+    >>> G.add_edge("a", "b", weight=3, capacity=4)
+    >>> G.add_edge("a", "c", weight=6, capacity=10)
+    >>> G.add_edge("b", "d", weight=1, capacity=9)
+    >>> G.add_edge("c", "d", weight=2, capacity=5)
+    >>> flowCost, flowDict = nx.capacity_scaling(G)
+    >>> flowCost
+    24
+    >>> flowDict
+    {'a': {'b': 4, 'c': 1}, 'd': {}, 'b': {'d': 4}, 'c': {'d': 1}}
+
+    It is possible to change the name of the attributes used for the
+    algorithm.
+
+    >>> G = nx.DiGraph()
+    >>> G.add_node("p", spam=-4)
+    >>> G.add_node("q", spam=2)
+    >>> G.add_node("a", spam=-2)
+    >>> G.add_node("d", spam=-1)
+    >>> G.add_node("t", spam=2)
+    >>> G.add_node("w", spam=3)
+    >>> G.add_edge("p", "q", cost=7, vacancies=5)
+    >>> G.add_edge("p", "a", cost=1, vacancies=4)
+    >>> G.add_edge("q", "d", cost=2, vacancies=3)
+    >>> G.add_edge("t", "q", cost=1, vacancies=2)
+    >>> G.add_edge("a", "t", cost=2, vacancies=4)
+    >>> G.add_edge("d", "w", cost=3, vacancies=4)
+    >>> G.add_edge("t", "w", cost=4, vacancies=1)
+    >>> flowCost, flowDict = nx.capacity_scaling(
+    ...     G, demand="spam", capacity="vacancies", weight="cost"
+    ... )
+    >>> flowCost
+    37
+    >>> flowDict
+    {'p': {'q': 2, 'a': 2}, 'q': {'d': 1}, 'a': {'t': 4}, 'd': {'w': 2}, 't': {'q': 1, 'w': 1}, 'w': {}}
+    """
+    R = _build_residual_network(G, demand, capacity, weight)
+
+    inf = float("inf")
+    # Account cost of negative selfloops.
+    flow_cost = sum(
+        0
+        if e.get(capacity, inf) <= 0 or e.get(weight, 0) >= 0
+        else e[capacity] * e[weight]
+        for u, v, e in nx.selfloop_edges(G, data=True)
+    )
+
+    # Determine the maximum edge capacity.
+    wmax = max(chain([-inf], (e["capacity"] for u, v, e in R.edges(data=True))))
+    if wmax == -inf:
+        # Residual network has no edges.
+        return flow_cost, _build_flow_dict(G, R, capacity, weight)
+
+    R_nodes = R.nodes
+    R_succ = R.succ
+
+    delta = 2 ** int(log(wmax, 2))
+    while delta >= 1:
+        # Saturate Δ-residual edges with negative reduced costs to achieve
+        # Δ-optimality.
+        for u in R:
+            p_u = R_nodes[u]["potential"]
+            for v, es in R_succ[u].items():
+                for k, e in es.items():
+                    flow = e["capacity"] - e["flow"]
+                    if e["weight"] - p_u + R_nodes[v]["potential"] < 0:
+                        flow = e["capacity"] - e["flow"]
+                        if flow >= delta:
+                            e["flow"] += flow
+                            R_succ[v][u][(k[0], not k[1])]["flow"] -= flow
+                            R_nodes[u]["excess"] -= flow
+                            R_nodes[v]["excess"] += flow
+        # Determine the Δ-active nodes.
+        S = set()
+        T = set()
+        S_add = S.add
+        S_remove = S.remove
+        T_add = T.add
+        T_remove = T.remove
+        for u in R:
+            excess = R_nodes[u]["excess"]
+            if excess >= delta:
+                S_add(u)
+            elif excess <= -delta:
+                T_add(u)
+        # Repeatedly augment flow from S to T along shortest paths until
+        # Δ-feasibility is achieved.
+        while S and T:
+            s = arbitrary_element(S)
+            t = None
+            # Search for a shortest path in terms of reduce costs from s to
+            # any t in T in the Δ-residual network.
+            d = {}
+            pred = {s: None}
+            h = heap()
+            h_insert = h.insert
+            h_get = h.get
+            h_insert(s, 0)
+            while h:
+                u, d_u = h.pop()
+                d[u] = d_u
+                if u in T:
+                    # Path found.
+                    t = u
+                    break
+                p_u = R_nodes[u]["potential"]
+                for v, es in R_succ[u].items():
+                    if v in d:
+                        continue
+                    wmin = inf
+                    # Find the minimum-weighted (u, v) Δ-residual edge.
+                    for k, e in es.items():
+                        if e["capacity"] - e["flow"] >= delta:
+                            w = e["weight"]
+                            if w < wmin:
+                                wmin = w
+                                kmin = k
+                                emin = e
+                    if wmin == inf:
+                        continue
+                    # Update the distance label of v.
+                    d_v = d_u + wmin - p_u + R_nodes[v]["potential"]
+                    if h_insert(v, d_v):
+                        pred[v] = (u, kmin, emin)
+            if t is not None:
+                # Augment Δ units of flow from s to t.
+                while u != s:
+                    v = u
+                    u, k, e = pred[v]
+                    e["flow"] += delta
+                    R_succ[v][u][(k[0], not k[1])]["flow"] -= delta
+                # Account node excess and deficit.
+                R_nodes[s]["excess"] -= delta
+                R_nodes[t]["excess"] += delta
+                if R_nodes[s]["excess"] < delta:
+                    S_remove(s)
+                if R_nodes[t]["excess"] > -delta:
+                    T_remove(t)
+                # Update node potentials.
+                d_t = d[t]
+                for u, d_u in d.items():
+                    R_nodes[u]["potential"] -= d_u - d_t
+            else:
+                # Path not found.
+                S_remove(s)
+        delta //= 2
+
+    if any(R.nodes[u]["excess"] != 0 for u in R):
+        raise nx.NetworkXUnfeasible("No flow satisfying all demands.")
+
+    # Calculate the flow cost.
+    for u in R:
+        for v, es in R_succ[u].items():
+            for e in es.values():
+                flow = e["flow"]
+                if flow > 0:
+                    flow_cost += flow * e["weight"]
+
+    return flow_cost, _build_flow_dict(G, R, capacity, weight)

janus/lib/python3.10/site-packages/networkx/algorithms/flow/dinitz_alg.py

@@ -0,0 +1,238 @@
+"""
+Dinitz' algorithm for maximum flow problems.
+"""
+
+from collections import deque
+
+import networkx as nx
+from networkx.algorithms.flow.utils import build_residual_network
+from networkx.utils import pairwise
+
+__all__ = ["dinitz"]
+
+
+@nx._dispatchable(edge_attrs={"capacity": float("inf")}, returns_graph=True)
+def dinitz(G, s, t, capacity="capacity", residual=None, value_only=False, cutoff=None):
+    """Find a maximum single-commodity flow using Dinitz' algorithm.
+
+    This function returns the residual network resulting after computing
+    the maximum flow. See below for details about the conventions
+    NetworkX uses for defining residual networks.
+
+    This algorithm has a running time of $O(n^2 m)$ for $n$ nodes and $m$
+    edges [1]_.
+
+
+    Parameters
+    ----------
+    G : NetworkX graph
+        Edges of the graph are expected to have an attribute called
+        'capacity'. If this attribute is not present, the edge is
+        considered to have infinite capacity.
+
+    s : node
+        Source node for the flow.
+
+    t : node
+        Sink node for the flow.
+
+    capacity : string
+        Edges of the graph G are expected to have an attribute capacity
+        that indicates how much flow the edge can support. If this
+        attribute is not present, the edge is considered to have
+        infinite capacity. Default value: 'capacity'.
+
+    residual : NetworkX graph
+        Residual network on which the algorithm is to be executed. If None, a
+        new residual network is created. Default value: None.
+
+    value_only : bool
+        If True compute only the value of the maximum flow. This parameter
+        will be ignored by this algorithm because it is not applicable.
+
+    cutoff : integer, float
+        If specified, the algorithm will terminate when the flow value reaches
+        or exceeds the cutoff. In this case, it may be unable to immediately
+        determine a minimum cut. Default value: None.
+
+    Returns
+    -------
+    R : NetworkX DiGraph
+        Residual network after computing the maximum flow.
+
+    Raises
+    ------
+    NetworkXError
+        The algorithm does not support MultiGraph and MultiDiGraph. If
+        the input graph is an instance of one of these two classes, a
+        NetworkXError is raised.
+
+    NetworkXUnbounded
+        If the graph has a path of infinite capacity, the value of a
+        feasible flow on the graph is unbounded above and the function
+        raises a NetworkXUnbounded.
+
+    See also
+    --------
+    :meth:`maximum_flow`
+    :meth:`minimum_cut`
+    :meth:`preflow_push`
+    :meth:`shortest_augmenting_path`
+
+    Notes
+    -----
+    The residual network :samp:`R` from an input graph :samp:`G` has the
+    same nodes as :samp:`G`. :samp:`R` is a DiGraph that contains a pair
+    of edges :samp:`(u, v)` and :samp:`(v, u)` iff :samp:`(u, v)` is not a
+    self-loop, and at least one of :samp:`(u, v)` and :samp:`(v, u)` exists
+    in :samp:`G`.
+
+    For each edge :samp:`(u, v)` in :samp:`R`, :samp:`R[u][v]['capacity']`
+    is equal to the capacity of :samp:`(u, v)` in :samp:`G` if it exists
+    in :samp:`G` or zero otherwise. If the capacity is infinite,
+    :samp:`R[u][v]['capacity']` will have a high arbitrary finite value
+    that does not affect the solution of the problem. This value is stored in
+    :samp:`R.graph['inf']`. For each edge :samp:`(u, v)` in :samp:`R`,
+    :samp:`R[u][v]['flow']` represents the flow function of :samp:`(u, v)` and
+    satisfies :samp:`R[u][v]['flow'] == -R[v][u]['flow']`.
+
+    The flow value, defined as the total flow into :samp:`t`, the sink, is
+    stored in :samp:`R.graph['flow_value']`. If :samp:`cutoff` is not
+    specified, reachability to :samp:`t` using only edges :samp:`(u, v)` such
+    that :samp:`R[u][v]['flow'] < R[u][v]['capacity']` induces a minimum
+    :samp:`s`-:samp:`t` cut.
+
+    Examples
+    --------
+    >>> from networkx.algorithms.flow import dinitz
+
+    The functions that implement flow algorithms and output a residual
+    network, such as this one, are not imported to the base NetworkX
+    namespace, so you have to explicitly import them from the flow package.
+
+    >>> G = nx.DiGraph()
+    >>> G.add_edge("x", "a", capacity=3.0)
+    >>> G.add_edge("x", "b", capacity=1.0)
+    >>> G.add_edge("a", "c", capacity=3.0)
+    >>> G.add_edge("b", "c", capacity=5.0)
+    >>> G.add_edge("b", "d", capacity=4.0)
+    >>> G.add_edge("d", "e", capacity=2.0)
+    >>> G.add_edge("c", "y", capacity=2.0)
+    >>> G.add_edge("e", "y", capacity=3.0)
+    >>> R = dinitz(G, "x", "y")
+    >>> flow_value = nx.maximum_flow_value(G, "x", "y")
+    >>> flow_value
+    3.0
+    >>> flow_value == R.graph["flow_value"]
+    True
+
+    References
+    ----------
+    .. [1] Dinitz' Algorithm: The Original Version and Even's Version.
+           2006. Yefim Dinitz. In Theoretical Computer Science. Lecture
+           Notes in Computer Science. Volume 3895. pp 218-240.
+           https://doi.org/10.1007/11685654_10
+
+    """
+    R = dinitz_impl(G, s, t, capacity, residual, cutoff)
+    R.graph["algorithm"] = "dinitz"
+    nx._clear_cache(R)
+    return R
+
+
+def dinitz_impl(G, s, t, capacity, residual, cutoff):
+    if s not in G:
+        raise nx.NetworkXError(f"node {str(s)} not in graph")
+    if t not in G:
+        raise nx.NetworkXError(f"node {str(t)} not in graph")
+    if s == t:
+        raise nx.NetworkXError("source and sink are the same node")
+
+    if residual is None:
+        R = build_residual_network(G, capacity)
+    else:
+        R = residual
+
+    # Initialize/reset the residual network.
+    for u in R:
+        for e in R[u].values():
+            e["flow"] = 0
+
+    # Use an arbitrary high value as infinite. It is computed
+    # when building the residual network.
+    INF = R.graph["inf"]
+
+    if cutoff is None:
+        cutoff = INF
+
+    R_succ = R.succ
+    R_pred = R.pred
+
+    def breath_first_search():
+        parents = {}
+        vertex_dist = {s: 0}
+        queue = deque([(s, 0)])
+        # Record all the potential edges of shortest augmenting paths
+        while queue:
+            if t in parents:
+                break
+            u, dist = queue.popleft()
+            for v, attr in R_succ[u].items():
+                if attr["capacity"] - attr["flow"] > 0:
+                    if v in parents:
+                        if vertex_dist[v] == dist + 1:
+                            parents[v].append(u)
+                    else:
+                        parents[v] = deque([u])
+                        vertex_dist[v] = dist + 1
+                        queue.append((v, dist + 1))
+        return parents
+
+    def depth_first_search(parents):
+        # DFS to find all the shortest augmenting paths
+        """Build a path using DFS starting from the sink"""
+        total_flow = 0
+        u = t
+        # path also functions as a stack
+        path = [u]
+        # The loop ends with no augmenting path left in the layered graph
+        while True:
+            if len(parents[u]) > 0:
+                v = parents[u][0]
+                path.append(v)
+            else:
+                path.pop()
+                if len(path) == 0:
+                    break
+                v = path[-1]
+                parents[v].popleft()
+            # Augment the flow along the path found
+            if v == s:
+                flow = INF
+                for u, v in pairwise(path):
+                    flow = min(flow, R_pred[u][v]["capacity"] - R_pred[u][v]["flow"])
+                for u, v in pairwise(reversed(path)):
+                    R_pred[v][u]["flow"] += flow
+                    R_pred[u][v]["flow"] -= flow
+                    # Find the proper node to continue the search
+                    if R_pred[v][u]["capacity"] - R_pred[v][u]["flow"] == 0:
+                        parents[v].popleft()
+                        while path[-1] != v:
+                            path.pop()
+                total_flow += flow
+                v = path[-1]
+            u = v
+        return total_flow
+
+    flow_value = 0
+    while flow_value < cutoff:
+        parents = breath_first_search()
+        if t not in parents:
+            break
+        this_flow = depth_first_search(parents)
+        if this_flow * 2 > INF:
+            raise nx.NetworkXUnbounded("Infinite capacity path, flow unbounded above.")
+        flow_value += this_flow
+
+    R.graph["flow_value"] = flow_value
+    return R

janus/lib/python3.10/site-packages/networkx/algorithms/flow/edmondskarp.py

@@ -0,0 +1,241 @@
+"""
+Edmonds-Karp algorithm for maximum flow problems.
+"""
+
+import networkx as nx
+from networkx.algorithms.flow.utils import build_residual_network
+
+__all__ = ["edmonds_karp"]
+
+
+def edmonds_karp_core(R, s, t, cutoff):
+    """Implementation of the Edmonds-Karp algorithm."""
+    R_nodes = R.nodes
+    R_pred = R.pred
+    R_succ = R.succ
+
+    inf = R.graph["inf"]
+
+    def augment(path):
+        """Augment flow along a path from s to t."""
+        # Determine the path residual capacity.
+        flow = inf
+        it = iter(path)
+        u = next(it)
+        for v in it:
+            attr = R_succ[u][v]
+            flow = min(flow, attr["capacity"] - attr["flow"])
+            u = v
+        if flow * 2 > inf:
+            raise nx.NetworkXUnbounded("Infinite capacity path, flow unbounded above.")
+        # Augment flow along the path.
+        it = iter(path)
+        u = next(it)
+        for v in it:
+            R_succ[u][v]["flow"] += flow
+            R_succ[v][u]["flow"] -= flow
+            u = v
+        return flow
+
+    def bidirectional_bfs():
+        """Bidirectional breadth-first search for an augmenting path."""
+        pred = {s: None}
+        q_s = [s]
+        succ = {t: None}
+        q_t = [t]
+        while True:
+            q = []
+            if len(q_s) <= len(q_t):
+                for u in q_s:
+                    for v, attr in R_succ[u].items():
+                        if v not in pred and attr["flow"] < attr["capacity"]:
+                            pred[v] = u
+                            if v in succ:
+                                return v, pred, succ
+                            q.append(v)
+                if not q:
+                    return None, None, None
+                q_s = q
+            else:
+                for u in q_t:
+                    for v, attr in R_pred[u].items():
+                        if v not in succ and attr["flow"] < attr["capacity"]:
+                            succ[v] = u
+                            if v in pred:
+                                return v, pred, succ
+                            q.append(v)
+                if not q:
+                    return None, None, None
+                q_t = q
+
+    # Look for shortest augmenting paths using breadth-first search.
+    flow_value = 0
+    while flow_value < cutoff:
+        v, pred, succ = bidirectional_bfs()
+        if pred is None:
+            break
+        path = [v]
+        # Trace a path from s to v.
+        u = v
+        while u != s:
+            u = pred[u]
+            path.append(u)
+        path.reverse()
+        # Trace a path from v to t.
+        u = v
+        while u != t:
+            u = succ[u]
+            path.append(u)
+        flow_value += augment(path)
+
+    return flow_value
+
+
+def edmonds_karp_impl(G, s, t, capacity, residual, cutoff):
+    """Implementation of the Edmonds-Karp algorithm."""
+    if s not in G:
+        raise nx.NetworkXError(f"node {str(s)} not in graph")
+    if t not in G:
+        raise nx.NetworkXError(f"node {str(t)} not in graph")
+    if s == t:
+        raise nx.NetworkXError("source and sink are the same node")
+
+    if residual is None:
+        R = build_residual_network(G, capacity)
+    else:
+        R = residual
+
+    # Initialize/reset the residual network.
+    for u in R:
+        for e in R[u].values():
+            e["flow"] = 0
+
+    if cutoff is None:
+        cutoff = float("inf")
+    R.graph["flow_value"] = edmonds_karp_core(R, s, t, cutoff)
+
+    return R
+
+
+@nx._dispatchable(edge_attrs={"capacity": float("inf")}, returns_graph=True)
+def edmonds_karp(
+    G, s, t, capacity="capacity", residual=None, value_only=False, cutoff=None
+):
+    """Find a maximum single-commodity flow using the Edmonds-Karp algorithm.
+
+    This function returns the residual network resulting after computing
+    the maximum flow. See below for details about the conventions
+    NetworkX uses for defining residual networks.
+
+    This algorithm has a running time of $O(n m^2)$ for $n$ nodes and $m$
+    edges.
+
+
+    Parameters
+    ----------
+    G : NetworkX graph
+        Edges of the graph are expected to have an attribute called
+        'capacity'. If this attribute is not present, the edge is
+        considered to have infinite capacity.
+
+    s : node
+        Source node for the flow.
+
+    t : node
+        Sink node for the flow.
+
+    capacity : string
+        Edges of the graph G are expected to have an attribute capacity
+        that indicates how much flow the edge can support. If this
+        attribute is not present, the edge is considered to have
+        infinite capacity. Default value: 'capacity'.
+
+    residual : NetworkX graph
+        Residual network on which the algorithm is to be executed. If None, a
+        new residual network is created. Default value: None.
+
+    value_only : bool
+        If True compute only the value of the maximum flow. This parameter
+        will be ignored by this algorithm because it is not applicable.
+
+    cutoff : integer, float
+        If specified, the algorithm will terminate when the flow value reaches
+        or exceeds the cutoff. In this case, it may be unable to immediately
+        determine a minimum cut. Default value: None.
+
+    Returns
+    -------
+    R : NetworkX DiGraph
+        Residual network after computing the maximum flow.
+
+    Raises
+    ------
+    NetworkXError
+        The algorithm does not support MultiGraph and MultiDiGraph. If
+        the input graph is an instance of one of these two classes, a
+        NetworkXError is raised.
+
+    NetworkXUnbounded
+        If the graph has a path of infinite capacity, the value of a
+        feasible flow on the graph is unbounded above and the function
+        raises a NetworkXUnbounded.
+
+    See also
+    --------
+    :meth:`maximum_flow`
+    :meth:`minimum_cut`
+    :meth:`preflow_push`
+    :meth:`shortest_augmenting_path`
+
+    Notes
+    -----
+    The residual network :samp:`R` from an input graph :samp:`G` has the
+    same nodes as :samp:`G`. :samp:`R` is a DiGraph that contains a pair
+    of edges :samp:`(u, v)` and :samp:`(v, u)` iff :samp:`(u, v)` is not a
+    self-loop, and at least one of :samp:`(u, v)` and :samp:`(v, u)` exists
+    in :samp:`G`.
+
+    For each edge :samp:`(u, v)` in :samp:`R`, :samp:`R[u][v]['capacity']`
+    is equal to the capacity of :samp:`(u, v)` in :samp:`G` if it exists
+    in :samp:`G` or zero otherwise. If the capacity is infinite,
+    :samp:`R[u][v]['capacity']` will have a high arbitrary finite value
+    that does not affect the solution of the problem. This value is stored in
+    :samp:`R.graph['inf']`. For each edge :samp:`(u, v)` in :samp:`R`,
+    :samp:`R[u][v]['flow']` represents the flow function of :samp:`(u, v)` and
+    satisfies :samp:`R[u][v]['flow'] == -R[v][u]['flow']`.
+
+    The flow value, defined as the total flow into :samp:`t`, the sink, is
+    stored in :samp:`R.graph['flow_value']`. If :samp:`cutoff` is not
+    specified, reachability to :samp:`t` using only edges :samp:`(u, v)` such
+    that :samp:`R[u][v]['flow'] < R[u][v]['capacity']` induces a minimum
+    :samp:`s`-:samp:`t` cut.
+
+    Examples
+    --------
+    >>> from networkx.algorithms.flow import edmonds_karp
+
+    The functions that implement flow algorithms and output a residual
+    network, such as this one, are not imported to the base NetworkX
+    namespace, so you have to explicitly import them from the flow package.
+
+    >>> G = nx.DiGraph()
+    >>> G.add_edge("x", "a", capacity=3.0)
+    >>> G.add_edge("x", "b", capacity=1.0)
+    >>> G.add_edge("a", "c", capacity=3.0)
+    >>> G.add_edge("b", "c", capacity=5.0)
+    >>> G.add_edge("b", "d", capacity=4.0)
+    >>> G.add_edge("d", "e", capacity=2.0)
+    >>> G.add_edge("c", "y", capacity=2.0)
+    >>> G.add_edge("e", "y", capacity=3.0)
+    >>> R = edmonds_karp(G, "x", "y")
+    >>> flow_value = nx.maximum_flow_value(G, "x", "y")
+    >>> flow_value
+    3.0
+    >>> flow_value == R.graph["flow_value"]
+    True
+
+    """
+    R = edmonds_karp_impl(G, s, t, capacity, residual, cutoff)
+    R.graph["algorithm"] = "edmonds_karp"
+    nx._clear_cache(R)
+    return R

janus/lib/python3.10/site-packages/networkx/algorithms/flow/gomory_hu.py

@@ -0,0 +1,178 @@
+"""
+Gomory-Hu tree of undirected Graphs.
+"""
+
+import networkx as nx
+from networkx.utils import not_implemented_for
+
+from .edmondskarp import edmonds_karp
+from .utils import build_residual_network
+
+default_flow_func = edmonds_karp
+
+__all__ = ["gomory_hu_tree"]
+
+
+@not_implemented_for("directed")
+@nx._dispatchable(edge_attrs={"capacity": float("inf")}, returns_graph=True)
+def gomory_hu_tree(G, capacity="capacity", flow_func=None):
+    r"""Returns the Gomory-Hu tree of an undirected graph G.
+
+    A Gomory-Hu tree of an undirected graph with capacities is a
+    weighted tree that represents the minimum s-t cuts for all s-t
+    pairs in the graph.
+
+    It only requires `n-1` minimum cut computations instead of the
+    obvious `n(n-1)/2`. The tree represents all s-t cuts as the
+    minimum cut value among any pair of nodes is the minimum edge
+    weight in the shortest path between the two nodes in the
+    Gomory-Hu tree.
+
+    The Gomory-Hu tree also has the property that removing the
+    edge with the minimum weight in the shortest path between
+    any two nodes leaves two connected components that form
+    a partition of the nodes in G that defines the minimum s-t
+    cut.
+
+    See Examples section below for details.
+
+    Parameters
+    ----------
+    G : NetworkX graph
+        Undirected graph
+
+    capacity : string
+        Edges of the graph G are expected to have an attribute capacity
+        that indicates how much flow the edge can support. If this
+        attribute is not present, the edge is considered to have
+        infinite capacity. Default value: 'capacity'.
+
+    flow_func : function
+        Function to perform the underlying flow computations. Default value
+        :func:`edmonds_karp`. This function performs better in sparse graphs
+        with right tailed degree distributions.
+        :func:`shortest_augmenting_path` will perform better in denser
+        graphs.
+
+    Returns
+    -------
+    Tree : NetworkX graph
+        A NetworkX graph representing the Gomory-Hu tree of the input graph.
+
+    Raises
+    ------
+    NetworkXNotImplemented
+        Raised if the input graph is directed.
+
+    NetworkXError
+        Raised if the input graph is an empty Graph.
+
+    Examples
+    --------
+    >>> G = nx.karate_club_graph()
+    >>> nx.set_edge_attributes(G, 1, "capacity")
+    >>> T = nx.gomory_hu_tree(G)
+    >>> # The value of the minimum cut between any pair
+    ... # of nodes in G is the minimum edge weight in the
+    ... # shortest path between the two nodes in the
+    ... # Gomory-Hu tree.
+    ... def minimum_edge_weight_in_shortest_path(T, u, v):
+    ...     path = nx.shortest_path(T, u, v, weight="weight")
+    ...     return min((T[u][v]["weight"], (u, v)) for (u, v) in zip(path, path[1:]))
+    >>> u, v = 0, 33
+    >>> cut_value, edge = minimum_edge_weight_in_shortest_path(T, u, v)
+    >>> cut_value
+    10
+    >>> nx.minimum_cut_value(G, u, v)
+    10
+    >>> # The Gomory-Hu tree also has the property that removing the
+    ... # edge with the minimum weight in the shortest path between
+    ... # any two nodes leaves two connected components that form
+    ... # a partition of the nodes in G that defines the minimum s-t
+    ... # cut.
+    ... cut_value, edge = minimum_edge_weight_in_shortest_path(T, u, v)
+    >>> T.remove_edge(*edge)
+    >>> U, V = list(nx.connected_components(T))
+    >>> # Thus U and V form a partition that defines a minimum cut
+    ... # between u and v in G. You can compute the edge cut set,
+    ... # that is, the set of edges that if removed from G will
+    ... # disconnect u from v in G, with this information:
+    ... cutset = set()
+    >>> for x, nbrs in ((n, G[n]) for n in U):
+    ...     cutset.update((x, y) for y in nbrs if y in V)
+    >>> # Because we have set the capacities of all edges to 1
+    ... # the cutset contains ten edges
+    ... len(cutset)
+    10
+    >>> # You can use any maximum flow algorithm for the underlying
+    ... # flow computations using the argument flow_func
+    ... from networkx.algorithms import flow
+    >>> T = nx.gomory_hu_tree(G, flow_func=flow.boykov_kolmogorov)
+    >>> cut_value, edge = minimum_edge_weight_in_shortest_path(T, u, v)
+    >>> cut_value
+    10
+    >>> nx.minimum_cut_value(G, u, v, flow_func=flow.boykov_kolmogorov)
+    10
+
+    Notes
+    -----
+    This implementation is based on Gusfield approach [1]_ to compute
+    Gomory-Hu trees, which does not require node contractions and has
+    the same computational complexity than the original method.
+
+    See also
+    --------
+    :func:`minimum_cut`
+    :func:`maximum_flow`
+
+    References
+    ----------
+    .. [1] Gusfield D: Very simple methods for all pairs network flow analysis.
+           SIAM J Comput 19(1):143-155, 1990.
+
+    """
+    if flow_func is None:
+        flow_func = default_flow_func
+
+    if len(G) == 0:  # empty graph
+        msg = "Empty Graph does not have a Gomory-Hu tree representation"
+        raise nx.NetworkXError(msg)
+
+    # Start the tree as a star graph with an arbitrary node at the center
+    tree = {}
+    labels = {}
+    iter_nodes = iter(G)
+    root = next(iter_nodes)
+    for n in iter_nodes:
+        tree[n] = root
+
+    # Reuse residual network
+    R = build_residual_network(G, capacity)
+
+    # For all the leaves in the star graph tree (that is n-1 nodes).
+    for source in tree:
+        # Find neighbor in the tree
+        target = tree[source]
+        # compute minimum cut
+        cut_value, partition = nx.minimum_cut(
+            G, source, target, capacity=capacity, flow_func=flow_func, residual=R
+        )
+        labels[(source, target)] = cut_value
+        # Update the tree
+        # Source will always be in partition[0] and target in partition[1]
+        for node in partition[0]:
+            if node != source and node in tree and tree[node] == target:
+                tree[node] = source
+                labels[node, source] = labels.get((node, target), cut_value)
+        #
+        if target != root and tree[target] in partition[0]:
+            labels[source, tree[target]] = labels[target, tree[target]]
+            labels[target, source] = cut_value
+            tree[source] = tree[target]
+            tree[target] = source
+
+    # Build the tree
+    T = nx.Graph()
+    T.add_nodes_from(G)
+    T.add_weighted_edges_from(((u, v, labels[u, v]) for u, v in tree.items()))
+    return T

janus/lib/python3.10/site-packages/networkx/algorithms/flow/maxflow.py

@@ -0,0 +1,607 @@
+"""
+Maximum flow (and minimum cut) algorithms on capacitated graphs.
+"""
+
+import networkx as nx
+
+from .boykovkolmogorov import boykov_kolmogorov
+from .dinitz_alg import dinitz
+from .edmondskarp import edmonds_karp
+from .preflowpush import preflow_push
+from .shortestaugmentingpath import shortest_augmenting_path
+from .utils import build_flow_dict
+
+# Define the default flow function for computing maximum flow.
+default_flow_func = preflow_push
+
+__all__ = ["maximum_flow", "maximum_flow_value", "minimum_cut", "minimum_cut_value"]
+
+
+@nx._dispatchable(graphs="flowG", edge_attrs={"capacity": float("inf")})
+def maximum_flow(flowG, _s, _t, capacity="capacity", flow_func=None, **kwargs):
+    """Find a maximum single-commodity flow.
+
+    Parameters
+    ----------
+    flowG : NetworkX graph
+        Edges of the graph are expected to have an attribute called
+        'capacity'. If this attribute is not present, the edge is
+        considered to have infinite capacity.
+
+    _s : node
+        Source node for the flow.
+
+    _t : node
+        Sink node for the flow.
+
+    capacity : string
+        Edges of the graph G are expected to have an attribute capacity
+        that indicates how much flow the edge can support. If this
+        attribute is not present, the edge is considered to have
+        infinite capacity. Default value: 'capacity'.
+
+    flow_func : function
+        A function for computing the maximum flow among a pair of nodes
+        in a capacitated graph. The function has to accept at least three
+        parameters: a Graph or Digraph, a source node, and a target node.
+        And return a residual network that follows NetworkX conventions
+        (see Notes). If flow_func is None, the default maximum
+        flow function (:meth:`preflow_push`) is used. See below for
+        alternative algorithms. The choice of the default function may change
+        from version to version and should not be relied on. Default value:
+        None.
+
+    kwargs : Any other keyword parameter is passed to the function that
+        computes the maximum flow.
+
+    Returns
+    -------
+    flow_value : integer, float
+        Value of the maximum flow, i.e., net outflow from the source.
+
+    flow_dict : dict
+        A dictionary containing the value of the flow that went through
+        each edge.
+
+    Raises
+    ------
+    NetworkXError
+        The algorithm does not support MultiGraph and MultiDiGraph. If
+        the input graph is an instance of one of these two classes, a
+        NetworkXError is raised.
+
+    NetworkXUnbounded
+        If the graph has a path of infinite capacity, the value of a
+        feasible flow on the graph is unbounded above and the function
+        raises a NetworkXUnbounded.
+
+    See also
+    --------
+    :meth:`maximum_flow_value`
+    :meth:`minimum_cut`
+    :meth:`minimum_cut_value`
+    :meth:`edmonds_karp`
+    :meth:`preflow_push`
+    :meth:`shortest_augmenting_path`
+
+    Notes
+    -----
+    The function used in the flow_func parameter has to return a residual
+    network that follows NetworkX conventions:
+
+    The residual network :samp:`R` from an input graph :samp:`G` has the
+    same nodes as :samp:`G`. :samp:`R` is a DiGraph that contains a pair
+    of edges :samp:`(u, v)` and :samp:`(v, u)` iff :samp:`(u, v)` is not a
+    self-loop, and at least one of :samp:`(u, v)` and :samp:`(v, u)` exists
+    in :samp:`G`.
+
+    For each edge :samp:`(u, v)` in :samp:`R`, :samp:`R[u][v]['capacity']`
+    is equal to the capacity of :samp:`(u, v)` in :samp:`G` if it exists
+    in :samp:`G` or zero otherwise. If the capacity is infinite,
+    :samp:`R[u][v]['capacity']` will have a high arbitrary finite value
+    that does not affect the solution of the problem. This value is stored in
+    :samp:`R.graph['inf']`. For each edge :samp:`(u, v)` in :samp:`R`,
+    :samp:`R[u][v]['flow']` represents the flow function of :samp:`(u, v)` and
+    satisfies :samp:`R[u][v]['flow'] == -R[v][u]['flow']`.
+
+    The flow value, defined as the total flow into :samp:`t`, the sink, is
+    stored in :samp:`R.graph['flow_value']`. Reachability to :samp:`t` using
+    only edges :samp:`(u, v)` such that
+    :samp:`R[u][v]['flow'] < R[u][v]['capacity']` induces a minimum
+    :samp:`s`-:samp:`t` cut.
+
+    Specific algorithms may store extra data in :samp:`R`.
+
+    The function should supports an optional boolean parameter value_only. When
+    True, it can optionally terminate the algorithm as soon as the maximum flow
+    value and the minimum cut can be determined.
+
+    Examples
+    --------
+    >>> G = nx.DiGraph()
+    >>> G.add_edge("x", "a", capacity=3.0)
+    >>> G.add_edge("x", "b", capacity=1.0)
+    >>> G.add_edge("a", "c", capacity=3.0)
+    >>> G.add_edge("b", "c", capacity=5.0)
+    >>> G.add_edge("b", "d", capacity=4.0)
+    >>> G.add_edge("d", "e", capacity=2.0)
+    >>> G.add_edge("c", "y", capacity=2.0)
+    >>> G.add_edge("e", "y", capacity=3.0)
+
+    maximum_flow returns both the value of the maximum flow and a
+    dictionary with all flows.
+
+    >>> flow_value, flow_dict = nx.maximum_flow(G, "x", "y")
+    >>> flow_value
+    3.0
+    >>> print(flow_dict["x"]["b"])
+    1.0
+
+    You can also use alternative algorithms for computing the
+    maximum flow by using the flow_func parameter.
+
+    >>> from networkx.algorithms.flow import shortest_augmenting_path
+    >>> flow_value == nx.maximum_flow(G, "x", "y", flow_func=shortest_augmenting_path)[
+    ...     0
+    ... ]
+    True
+
+    """
+    if flow_func is None:
+        if kwargs:
+            raise nx.NetworkXError(
+                "You have to explicitly set a flow_func if"
+                " you need to pass parameters via kwargs."
+            )
+        flow_func = default_flow_func
+
+    if not callable(flow_func):
+        raise nx.NetworkXError("flow_func has to be callable.")
+
+    R = flow_func(flowG, _s, _t, capacity=capacity, value_only=False, **kwargs)
+    flow_dict = build_flow_dict(flowG, R)
+
+    return (R.graph["flow_value"], flow_dict)
+
+
+@nx._dispatchable(graphs="flowG", edge_attrs={"capacity": float("inf")})
+def maximum_flow_value(flowG, _s, _t, capacity="capacity", flow_func=None, **kwargs):
+    """Find the value of maximum single-commodity flow.
+
+    Parameters
+    ----------
+    flowG : NetworkX graph
+        Edges of the graph are expected to have an attribute called
+        'capacity'. If this attribute is not present, the edge is
+        considered to have infinite capacity.
+
+    _s : node
+        Source node for the flow.
+
+    _t : node
+        Sink node for the flow.
+
+    capacity : string
+        Edges of the graph G are expected to have an attribute capacity
+        that indicates how much flow the edge can support. If this
+        attribute is not present, the edge is considered to have
+        infinite capacity. Default value: 'capacity'.
+
+    flow_func : function
+        A function for computing the maximum flow among a pair of nodes
+        in a capacitated graph. The function has to accept at least three
+        parameters: a Graph or Digraph, a source node, and a target node.
+        And return a residual network that follows NetworkX conventions
+        (see Notes). If flow_func is None, the default maximum
+        flow function (:meth:`preflow_push`) is used. See below for
+        alternative algorithms. The choice of the default function may change
+        from version to version and should not be relied on. Default value:
+        None.
+
+    kwargs : Any other keyword parameter is passed to the function that
+        computes the maximum flow.
+
+    Returns
+    -------
+    flow_value : integer, float
+        Value of the maximum flow, i.e., net outflow from the source.
+
+    Raises
+    ------
+    NetworkXError
+        The algorithm does not support MultiGraph and MultiDiGraph. If
+        the input graph is an instance of one of these two classes, a
+        NetworkXError is raised.
+
+    NetworkXUnbounded
+        If the graph has a path of infinite capacity, the value of a
+        feasible flow on the graph is unbounded above and the function
+        raises a NetworkXUnbounded.
+
+    See also
+    --------
+    :meth:`maximum_flow`
+    :meth:`minimum_cut`
+    :meth:`minimum_cut_value`
+    :meth:`edmonds_karp`
+    :meth:`preflow_push`
+    :meth:`shortest_augmenting_path`
+
+    Notes
+    -----
+    The function used in the flow_func parameter has to return a residual
+    network that follows NetworkX conventions:
+
+    The residual network :samp:`R` from an input graph :samp:`G` has the
+    same nodes as :samp:`G`. :samp:`R` is a DiGraph that contains a pair
+    of edges :samp:`(u, v)` and :samp:`(v, u)` iff :samp:`(u, v)` is not a
+    self-loop, and at least one of :samp:`(u, v)` and :samp:`(v, u)` exists
+    in :samp:`G`.
+
+    For each edge :samp:`(u, v)` in :samp:`R`, :samp:`R[u][v]['capacity']`
+    is equal to the capacity of :samp:`(u, v)` in :samp:`G` if it exists
+    in :samp:`G` or zero otherwise. If the capacity is infinite,
+    :samp:`R[u][v]['capacity']` will have a high arbitrary finite value
+    that does not affect the solution of the problem. This value is stored in
+    :samp:`R.graph['inf']`. For each edge :samp:`(u, v)` in :samp:`R`,
+    :samp:`R[u][v]['flow']` represents the flow function of :samp:`(u, v)` and
+    satisfies :samp:`R[u][v]['flow'] == -R[v][u]['flow']`.
+
+    The flow value, defined as the total flow into :samp:`t`, the sink, is
+    stored in :samp:`R.graph['flow_value']`. Reachability to :samp:`t` using
+    only edges :samp:`(u, v)` such that
+    :samp:`R[u][v]['flow'] < R[u][v]['capacity']` induces a minimum
+    :samp:`s`-:samp:`t` cut.
+
+    Specific algorithms may store extra data in :samp:`R`.
+
+    The function should supports an optional boolean parameter value_only. When
+    True, it can optionally terminate the algorithm as soon as the maximum flow
+    value and the minimum cut can be determined.
+
+    Examples
+    --------
+    >>> G = nx.DiGraph()
+    >>> G.add_edge("x", "a", capacity=3.0)
+    >>> G.add_edge("x", "b", capacity=1.0)
+    >>> G.add_edge("a", "c", capacity=3.0)
+    >>> G.add_edge("b", "c", capacity=5.0)
+    >>> G.add_edge("b", "d", capacity=4.0)
+    >>> G.add_edge("d", "e", capacity=2.0)
+    >>> G.add_edge("c", "y", capacity=2.0)
+    >>> G.add_edge("e", "y", capacity=3.0)
+
+    maximum_flow_value computes only the value of the
+    maximum flow:
+
+    >>> flow_value = nx.maximum_flow_value(G, "x", "y")
+    >>> flow_value
+    3.0
+
+    You can also use alternative algorithms for computing the
+    maximum flow by using the flow_func parameter.
+
+    >>> from networkx.algorithms.flow import shortest_augmenting_path
+    >>> flow_value == nx.maximum_flow_value(
+    ...     G, "x", "y", flow_func=shortest_augmenting_path
+    ... )
+    True
+
+    """
+    if flow_func is None:
+        if kwargs:
+            raise nx.NetworkXError(
+                "You have to explicitly set a flow_func if"
+                " you need to pass parameters via kwargs."
+            )
+        flow_func = default_flow_func
+
+    if not callable(flow_func):
+        raise nx.NetworkXError("flow_func has to be callable.")
+
+    R = flow_func(flowG, _s, _t, capacity=capacity, value_only=True, **kwargs)
+
+    return R.graph["flow_value"]
+
+
+@nx._dispatchable(graphs="flowG", edge_attrs={"capacity": float("inf")})
+def minimum_cut(flowG, _s, _t, capacity="capacity", flow_func=None, **kwargs):
+    """Compute the value and the node partition of a minimum (s, t)-cut.
+
+    Use the max-flow min-cut theorem, i.e., the capacity of a minimum
+    capacity cut is equal to the flow value of a maximum flow.
+
+    Parameters
+    ----------
+    flowG : NetworkX graph
+        Edges of the graph are expected to have an attribute called
+        'capacity'. If this attribute is not present, the edge is
+        considered to have infinite capacity.
+
+    _s : node
+        Source node for the flow.
+
+    _t : node
+        Sink node for the flow.
+
+    capacity : string
+        Edges of the graph G are expected to have an attribute capacity
+        that indicates how much flow the edge can support. If this
+        attribute is not present, the edge is considered to have
+        infinite capacity. Default value: 'capacity'.
+
+    flow_func : function
+        A function for computing the maximum flow among a pair of nodes
+        in a capacitated graph. The function has to accept at least three
+        parameters: a Graph or Digraph, a source node, and a target node.
+        And return a residual network that follows NetworkX conventions
+        (see Notes). If flow_func is None, the default maximum
+        flow function (:meth:`preflow_push`) is used. See below for
+        alternative algorithms. The choice of the default function may change
+        from version to version and should not be relied on. Default value:
+        None.
+
+    kwargs : Any other keyword parameter is passed to the function that
+        computes the maximum flow.
+
+    Returns
+    -------
+    cut_value : integer, float
+        Value of the minimum cut.
+
+    partition : pair of node sets
+        A partitioning of the nodes that defines a minimum cut.
+
+    Raises
+    ------
+    NetworkXUnbounded
+        If the graph has a path of infinite capacity, all cuts have
+        infinite capacity and the function raises a NetworkXError.
+
+    See also
+    --------
+    :meth:`maximum_flow`
+    :meth:`maximum_flow_value`
+    :meth:`minimum_cut_value`
+    :meth:`edmonds_karp`
+    :meth:`preflow_push`
+    :meth:`shortest_augmenting_path`
+
+    Notes
+    -----
+    The function used in the flow_func parameter has to return a residual
+    network that follows NetworkX conventions:
+
+    The residual network :samp:`R` from an input graph :samp:`G` has the
+    same nodes as :samp:`G`. :samp:`R` is a DiGraph that contains a pair
+    of edges :samp:`(u, v)` and :samp:`(v, u)` iff :samp:`(u, v)` is not a
+    self-loop, and at least one of :samp:`(u, v)` and :samp:`(v, u)` exists
+    in :samp:`G`.
+
+    For each edge :samp:`(u, v)` in :samp:`R`, :samp:`R[u][v]['capacity']`
+    is equal to the capacity of :samp:`(u, v)` in :samp:`G` if it exists
+    in :samp:`G` or zero otherwise. If the capacity is infinite,
+    :samp:`R[u][v]['capacity']` will have a high arbitrary finite value
+    that does not affect the solution of the problem. This value is stored in
+    :samp:`R.graph['inf']`. For each edge :samp:`(u, v)` in :samp:`R`,
+    :samp:`R[u][v]['flow']` represents the flow function of :samp:`(u, v)` and
+    satisfies :samp:`R[u][v]['flow'] == -R[v][u]['flow']`.
+
+    The flow value, defined as the total flow into :samp:`t`, the sink, is
+    stored in :samp:`R.graph['flow_value']`. Reachability to :samp:`t` using
+    only edges :samp:`(u, v)` such that
+    :samp:`R[u][v]['flow'] < R[u][v]['capacity']` induces a minimum
+    :samp:`s`-:samp:`t` cut.
+
+    Specific algorithms may store extra data in :samp:`R`.
+
+    The function should supports an optional boolean parameter value_only. When
+    True, it can optionally terminate the algorithm as soon as the maximum flow
+    value and the minimum cut can be determined.
+
+    Examples
+    --------
+    >>> G = nx.DiGraph()
+    >>> G.add_edge("x", "a", capacity=3.0)
+    >>> G.add_edge("x", "b", capacity=1.0)
+    >>> G.add_edge("a", "c", capacity=3.0)
+    >>> G.add_edge("b", "c", capacity=5.0)
+    >>> G.add_edge("b", "d", capacity=4.0)
+    >>> G.add_edge("d", "e", capacity=2.0)
+    >>> G.add_edge("c", "y", capacity=2.0)
+    >>> G.add_edge("e", "y", capacity=3.0)
+
+    minimum_cut computes both the value of the
+    minimum cut and the node partition:
+
+    >>> cut_value, partition = nx.minimum_cut(G, "x", "y")
+    >>> reachable, non_reachable = partition
+
+    'partition' here is a tuple with the two sets of nodes that define
+    the minimum cut. You can compute the cut set of edges that induce
+    the minimum cut as follows:
+
+    >>> cutset = set()
+    >>> for u, nbrs in ((n, G[n]) for n in reachable):
+    ...     cutset.update((u, v) for v in nbrs if v in non_reachable)
+    >>> print(sorted(cutset))
+    [('c', 'y'), ('x', 'b')]
+    >>> cut_value == sum(G.edges[u, v]["capacity"] for (u, v) in cutset)
+    True
+
+    You can also use alternative algorithms for computing the
+    minimum cut by using the flow_func parameter.
+
+    >>> from networkx.algorithms.flow import shortest_augmenting_path
+    >>> cut_value == nx.minimum_cut(G, "x", "y", flow_func=shortest_augmenting_path)[0]
+    True
+
+    """
+    if flow_func is None:
+        if kwargs:
+            raise nx.NetworkXError(
+                "You have to explicitly set a flow_func if"
+                " you need to pass parameters via kwargs."
+            )
+        flow_func = default_flow_func
+
+    if not callable(flow_func):
+        raise nx.NetworkXError("flow_func has to be callable.")
+
+    if kwargs.get("cutoff") is not None and flow_func is preflow_push:
+        raise nx.NetworkXError("cutoff should not be specified.")
+
+    R = flow_func(flowG, _s, _t, capacity=capacity, value_only=True, **kwargs)
+    # Remove saturated edges from the residual network
+    cutset = [(u, v, d) for u, v, d in R.edges(data=True) if d["flow"] == d["capacity"]]
+    R.remove_edges_from(cutset)
+
+    # Then, reachable and non reachable nodes from source in the
+    # residual network form the node partition that defines
+    # the minimum cut.
+    non_reachable = set(dict(nx.shortest_path_length(R, target=_t)))
+    partition = (set(flowG) - non_reachable, non_reachable)
+    # Finally add again cutset edges to the residual network to make
+    # sure that it is reusable.
+    R.add_edges_from(cutset)
+    return (R.graph["flow_value"], partition)
+
+
+@nx._dispatchable(graphs="flowG", edge_attrs={"capacity": float("inf")})
+def minimum_cut_value(flowG, _s, _t, capacity="capacity", flow_func=None, **kwargs):
+    """Compute the value of a minimum (s, t)-cut.
+
+    Use the max-flow min-cut theorem, i.e., the capacity of a minimum
+    capacity cut is equal to the flow value of a maximum flow.
+
+    Parameters
+    ----------
+    flowG : NetworkX graph
+        Edges of the graph are expected to have an attribute called
+        'capacity'. If this attribute is not present, the edge is
+        considered to have infinite capacity.
+
+    _s : node
+        Source node for the flow.
+
+    _t : node
+        Sink node for the flow.
+
+    capacity : string
+        Edges of the graph G are expected to have an attribute capacity
+        that indicates how much flow the edge can support. If this
+        attribute is not present, the edge is considered to have
+        infinite capacity. Default value: 'capacity'.
+
+    flow_func : function
+        A function for computing the maximum flow among a pair of nodes
+        in a capacitated graph. The function has to accept at least three
+        parameters: a Graph or Digraph, a source node, and a target node.
+        And return a residual network that follows NetworkX conventions
+        (see Notes). If flow_func is None, the default maximum
+        flow function (:meth:`preflow_push`) is used. See below for
+        alternative algorithms. The choice of the default function may change
+        from version to version and should not be relied on. Default value:
+        None.
+
+    kwargs : Any other keyword parameter is passed to the function that
+        computes the maximum flow.
+
+    Returns
+    -------
+    cut_value : integer, float
+        Value of the minimum cut.
+
+    Raises
+    ------
+    NetworkXUnbounded
+        If the graph has a path of infinite capacity, all cuts have
+        infinite capacity and the function raises a NetworkXError.
+
+    See also
+    --------
+    :meth:`maximum_flow`
+    :meth:`maximum_flow_value`
+    :meth:`minimum_cut`
+    :meth:`edmonds_karp`
+    :meth:`preflow_push`
+    :meth:`shortest_augmenting_path`
+
+    Notes
+    -----
+    The function used in the flow_func parameter has to return a residual
+    network that follows NetworkX conventions:
+
+    The residual network :samp:`R` from an input graph :samp:`G` has the
+    same nodes as :samp:`G`. :samp:`R` is a DiGraph that contains a pair
+    of edges :samp:`(u, v)` and :samp:`(v, u)` iff :samp:`(u, v)` is not a
+    self-loop, and at least one of :samp:`(u, v)` and :samp:`(v, u)` exists
+    in :samp:`G`.
+
+    For each edge :samp:`(u, v)` in :samp:`R`, :samp:`R[u][v]['capacity']`
+    is equal to the capacity of :samp:`(u, v)` in :samp:`G` if it exists
+    in :samp:`G` or zero otherwise. If the capacity is infinite,
+    :samp:`R[u][v]['capacity']` will have a high arbitrary finite value
+    that does not affect the solution of the problem. This value is stored in
+    :samp:`R.graph['inf']`. For each edge :samp:`(u, v)` in :samp:`R`,
+    :samp:`R[u][v]['flow']` represents the flow function of :samp:`(u, v)` and
+    satisfies :samp:`R[u][v]['flow'] == -R[v][u]['flow']`.
+
+    The flow value, defined as the total flow into :samp:`t`, the sink, is
+    stored in :samp:`R.graph['flow_value']`. Reachability to :samp:`t` using
+    only edges :samp:`(u, v)` such that
+    :samp:`R[u][v]['flow'] < R[u][v]['capacity']` induces a minimum
+    :samp:`s`-:samp:`t` cut.
+
+    Specific algorithms may store extra data in :samp:`R`.
+
+    The function should supports an optional boolean parameter value_only. When
+    True, it can optionally terminate the algorithm as soon as the maximum flow
+    value and the minimum cut can be determined.
+
+    Examples
+    --------
+    >>> G = nx.DiGraph()
+    >>> G.add_edge("x", "a", capacity=3.0)
+    >>> G.add_edge("x", "b", capacity=1.0)
+    >>> G.add_edge("a", "c", capacity=3.0)
+    >>> G.add_edge("b", "c", capacity=5.0)
+    >>> G.add_edge("b", "d", capacity=4.0)
+    >>> G.add_edge("d", "e", capacity=2.0)
+    >>> G.add_edge("c", "y", capacity=2.0)
+    >>> G.add_edge("e", "y", capacity=3.0)
+
+    minimum_cut_value computes only the value of the
+    minimum cut:
+
+    >>> cut_value = nx.minimum_cut_value(G, "x", "y")
+    >>> cut_value
+    3.0
+
+    You can also use alternative algorithms for computing the
+    minimum cut by using the flow_func parameter.
+
+    >>> from networkx.algorithms.flow import shortest_augmenting_path
+    >>> cut_value == nx.minimum_cut_value(
+    ...     G, "x", "y", flow_func=shortest_augmenting_path
+    ... )
+    True
+
+    """
+    if flow_func is None:
+        if kwargs:
+            raise nx.NetworkXError(
+                "You have to explicitly set a flow_func if"
+                " you need to pass parameters via kwargs."
+            )
+        flow_func = default_flow_func
+
+    if not callable(flow_func):
+        raise nx.NetworkXError("flow_func has to be callable.")
+
+    if kwargs.get("cutoff") is not None and flow_func is preflow_push:
+        raise nx.NetworkXError("cutoff should not be specified.")
+
+    R = flow_func(flowG, _s, _t, capacity=capacity, value_only=True, **kwargs)
+
+    return R.graph["flow_value"]

janus/lib/python3.10/site-packages/networkx/algorithms/flow/mincost.py

@@ -0,0 +1,356 @@
+"""
+Minimum cost flow algorithms on directed connected graphs.
+"""
+
+__all__ = ["min_cost_flow_cost", "min_cost_flow", "cost_of_flow", "max_flow_min_cost"]
+
+import networkx as nx
+
+
+@nx._dispatchable(
+    node_attrs="demand", edge_attrs={"capacity": float("inf"), "weight": 0}
+)
+def min_cost_flow_cost(G, demand="demand", capacity="capacity", weight="weight"):
+    r"""Find the cost of a minimum cost flow satisfying all demands in digraph G.
+
+    G is a digraph with edge costs and capacities and in which nodes
+    have demand, i.e., they want to send or receive some amount of
+    flow. A negative demand means that the node wants to send flow, a
+    positive demand means that the node want to receive flow. A flow on
+    the digraph G satisfies all demand if the net flow into each node
+    is equal to the demand of that node.
+
+    Parameters
+    ----------
+    G : NetworkX graph
+        DiGraph on which a minimum cost flow satisfying all demands is
+        to be found.
+
+    demand : string
+        Nodes of the graph G are expected to have an attribute demand
+        that indicates how much flow a node wants to send (negative
+        demand) or receive (positive demand). Note that the sum of the
+        demands should be 0 otherwise the problem in not feasible. If
+        this attribute is not present, a node is considered to have 0
+        demand. Default value: 'demand'.
+
+    capacity : string
+        Edges of the graph G are expected to have an attribute capacity
+        that indicates how much flow the edge can support. If this
+        attribute is not present, the edge is considered to have
+        infinite capacity. Default value: 'capacity'.
+
+    weight : string
+        Edges of the graph G are expected to have an attribute weight
+        that indicates the cost incurred by sending one unit of flow on
+        that edge. If not present, the weight is considered to be 0.
+        Default value: 'weight'.
+
+    Returns
+    -------
+    flowCost : integer, float
+        Cost of a minimum cost flow satisfying all demands.
+
+    Raises
+    ------
+    NetworkXError
+        This exception is raised if the input graph is not directed or
+        not connected.
+
+    NetworkXUnfeasible
+        This exception is raised in the following situations:
+
+            * The sum of the demands is not zero. Then, there is no
+              flow satisfying all demands.
+            * There is no flow satisfying all demand.
+
+    NetworkXUnbounded
+        This exception is raised if the digraph G has a cycle of
+        negative cost and infinite capacity. Then, the cost of a flow
+        satisfying all demands is unbounded below.
+
+    See also
+    --------
+    cost_of_flow, max_flow_min_cost, min_cost_flow, network_simplex
+
+    Notes
+    -----
+    This algorithm is not guaranteed to work if edge weights or demands
+    are floating point numbers (overflows and roundoff errors can
+    cause problems). As a workaround you can use integer numbers by
+    multiplying the relevant edge attributes by a convenient
+    constant factor (eg 100).
+
+    Examples
+    --------
+    A simple example of a min cost flow problem.
+
+    >>> G = nx.DiGraph()
+    >>> G.add_node("a", demand=-5)
+    >>> G.add_node("d", demand=5)
+    >>> G.add_edge("a", "b", weight=3, capacity=4)
+    >>> G.add_edge("a", "c", weight=6, capacity=10)
+    >>> G.add_edge("b", "d", weight=1, capacity=9)
+    >>> G.add_edge("c", "d", weight=2, capacity=5)
+    >>> flowCost = nx.min_cost_flow_cost(G)
+    >>> flowCost
+    24
+    """
+    return nx.network_simplex(G, demand=demand, capacity=capacity, weight=weight)[0]
+
+
+@nx._dispatchable(
+    node_attrs="demand", edge_attrs={"capacity": float("inf"), "weight": 0}
+)
+def min_cost_flow(G, demand="demand", capacity="capacity", weight="weight"):
+    r"""Returns a minimum cost flow satisfying all demands in digraph G.
+
+    G is a digraph with edge costs and capacities and in which nodes
+    have demand, i.e., they want to send or receive some amount of
+    flow. A negative demand means that the node wants to send flow, a
+    positive demand means that the node want to receive flow. A flow on
+    the digraph G satisfies all demand if the net flow into each node
+    is equal to the demand of that node.
+
+    Parameters
+    ----------
+    G : NetworkX graph
+        DiGraph on which a minimum cost flow satisfying all demands is
+        to be found.
+
+    demand : string
+        Nodes of the graph G are expected to have an attribute demand
+        that indicates how much flow a node wants to send (negative
+        demand) or receive (positive demand). Note that the sum of the
+        demands should be 0 otherwise the problem in not feasible. If
+        this attribute is not present, a node is considered to have 0
+        demand. Default value: 'demand'.
+
+    capacity : string
+        Edges of the graph G are expected to have an attribute capacity
+        that indicates how much flow the edge can support. If this
+        attribute is not present, the edge is considered to have
+        infinite capacity. Default value: 'capacity'.
+
+    weight : string
+        Edges of the graph G are expected to have an attribute weight
+        that indicates the cost incurred by sending one unit of flow on
+        that edge. If not present, the weight is considered to be 0.
+        Default value: 'weight'.
+
+    Returns
+    -------
+    flowDict : dictionary
+        Dictionary of dictionaries keyed by nodes such that
+        flowDict[u][v] is the flow edge (u, v).
+
+    Raises
+    ------
+    NetworkXError
+        This exception is raised if the input graph is not directed or
+        not connected.
+
+    NetworkXUnfeasible
+        This exception is raised in the following situations:
+
+            * The sum of the demands is not zero. Then, there is no
+              flow satisfying all demands.
+            * There is no flow satisfying all demand.
+
+    NetworkXUnbounded
+        This exception is raised if the digraph G has a cycle of
+        negative cost and infinite capacity. Then, the cost of a flow
+        satisfying all demands is unbounded below.
+
+    See also
+    --------
+    cost_of_flow, max_flow_min_cost, min_cost_flow_cost, network_simplex
+
+    Notes
+    -----
+    This algorithm is not guaranteed to work if edge weights or demands
+    are floating point numbers (overflows and roundoff errors can
+    cause problems). As a workaround you can use integer numbers by
+    multiplying the relevant edge attributes by a convenient
+    constant factor (eg 100).
+
+    Examples
+    --------
+    A simple example of a min cost flow problem.
+
+    >>> G = nx.DiGraph()
+    >>> G.add_node("a", demand=-5)
+    >>> G.add_node("d", demand=5)
+    >>> G.add_edge("a", "b", weight=3, capacity=4)
+    >>> G.add_edge("a", "c", weight=6, capacity=10)
+    >>> G.add_edge("b", "d", weight=1, capacity=9)
+    >>> G.add_edge("c", "d", weight=2, capacity=5)
+    >>> flowDict = nx.min_cost_flow(G)
+    >>> flowDict
+    {'a': {'b': 4, 'c': 1}, 'd': {}, 'b': {'d': 4}, 'c': {'d': 1}}
+    """
+    return nx.network_simplex(G, demand=demand, capacity=capacity, weight=weight)[1]
+
+
+@nx._dispatchable(edge_attrs={"weight": 0})
+def cost_of_flow(G, flowDict, weight="weight"):
+    """Compute the cost of the flow given by flowDict on graph G.
+
+    Note that this function does not check for the validity of the
+    flow flowDict. This function will fail if the graph G and the
+    flow don't have the same edge set.
+
+    Parameters
+    ----------
+    G : NetworkX graph
+        DiGraph on which a minimum cost flow satisfying all demands is
+        to be found.
+
+    weight : string
+        Edges of the graph G are expected to have an attribute weight
+        that indicates the cost incurred by sending one unit of flow on
+        that edge. If not present, the weight is considered to be 0.
+        Default value: 'weight'.
+
+    flowDict : dictionary
+        Dictionary of dictionaries keyed by nodes such that
+        flowDict[u][v] is the flow edge (u, v).
+
+    Returns
+    -------
+    cost : Integer, float
+        The total cost of the flow. This is given by the sum over all
+        edges of the product of the edge's flow and the edge's weight.
+
+    See also
+    --------
+    max_flow_min_cost, min_cost_flow, min_cost_flow_cost, network_simplex
+
+    Notes
+    -----
+    This algorithm is not guaranteed to work if edge weights or demands
+    are floating point numbers (overflows and roundoff errors can
+    cause problems). As a workaround you can use integer numbers by
+    multiplying the relevant edge attributes by a convenient
+    constant factor (eg 100).
+
+    Examples
+    --------
+    >>> G = nx.DiGraph()
+    >>> G.add_node("a", demand=-5)
+    >>> G.add_node("d", demand=5)
+    >>> G.add_edge("a", "b", weight=3, capacity=4)
+    >>> G.add_edge("a", "c", weight=6, capacity=10)
+    >>> G.add_edge("b", "d", weight=1, capacity=9)
+    >>> G.add_edge("c", "d", weight=2, capacity=5)
+    >>> flowDict = nx.min_cost_flow(G)
+    >>> flowDict
+    {'a': {'b': 4, 'c': 1}, 'd': {}, 'b': {'d': 4}, 'c': {'d': 1}}
+    >>> nx.cost_of_flow(G, flowDict)
+    24
+    """
+    return sum((flowDict[u][v] * d.get(weight, 0) for u, v, d in G.edges(data=True)))
+
+
+@nx._dispatchable(edge_attrs={"capacity": float("inf"), "weight": 0})
+def max_flow_min_cost(G, s, t, capacity="capacity", weight="weight"):
+    """Returns a maximum (s, t)-flow of minimum cost.
+
+    G is a digraph with edge costs and capacities. There is a source
+    node s and a sink node t. This function finds a maximum flow from
+    s to t whose total cost is minimized.
+
+    Parameters
+    ----------
+    G : NetworkX graph
+        DiGraph on which a minimum cost flow satisfying all demands is
+        to be found.
+
+    s: node label
+        Source of the flow.
+
+    t: node label
+        Destination of the flow.
+
+    capacity: string
+        Edges of the graph G are expected to have an attribute capacity
+        that indicates how much flow the edge can support. If this
+        attribute is not present, the edge is considered to have
+        infinite capacity. Default value: 'capacity'.
+
+    weight: string
+        Edges of the graph G are expected to have an attribute weight
+        that indicates the cost incurred by sending one unit of flow on
+        that edge. If not present, the weight is considered to be 0.
+        Default value: 'weight'.
+
+    Returns
+    -------
+    flowDict: dictionary
+        Dictionary of dictionaries keyed by nodes such that
+        flowDict[u][v] is the flow edge (u, v).
+
+    Raises
+    ------
+    NetworkXError
+        This exception is raised if the input graph is not directed or
+        not connected.
+
+    NetworkXUnbounded
+        This exception is raised if there is an infinite capacity path
+        from s to t in G. In this case there is no maximum flow. This
+        exception is also raised if the digraph G has a cycle of
+        negative cost and infinite capacity. Then, the cost of a flow
+        is unbounded below.
+
+    See also
+    --------
+    cost_of_flow, min_cost_flow, min_cost_flow_cost, network_simplex
+
+    Notes
+    -----
+    This algorithm is not guaranteed to work if edge weights or demands
+    are floating point numbers (overflows and roundoff errors can
+    cause problems). As a workaround you can use integer numbers by
+    multiplying the relevant edge attributes by a convenient
+    constant factor (eg 100).
+
+    Examples
+    --------
+    >>> G = nx.DiGraph()
+    >>> G.add_edges_from(
+    ...     [
+    ...         (1, 2, {"capacity": 12, "weight": 4}),
+    ...         (1, 3, {"capacity": 20, "weight": 6}),
+    ...         (2, 3, {"capacity": 6, "weight": -3}),
+    ...         (2, 6, {"capacity": 14, "weight": 1}),
+    ...         (3, 4, {"weight": 9}),
+    ...         (3, 5, {"capacity": 10, "weight": 5}),
+    ...         (4, 2, {"capacity": 19, "weight": 13}),
+    ...         (4, 5, {"capacity": 4, "weight": 0}),
+    ...         (5, 7, {"capacity": 28, "weight": 2}),
+    ...         (6, 5, {"capacity": 11, "weight": 1}),
+    ...         (6, 7, {"weight": 8}),
+    ...         (7, 4, {"capacity": 6, "weight": 6}),
+    ...     ]
+    ... )
+    >>> mincostFlow = nx.max_flow_min_cost(G, 1, 7)
+    >>> mincost = nx.cost_of_flow(G, mincostFlow)
+    >>> mincost
+    373
+    >>> from networkx.algorithms.flow import maximum_flow
+    >>> maxFlow = maximum_flow(G, 1, 7)[1]
+    >>> nx.cost_of_flow(G, maxFlow) >= mincost
+    True
+    >>> mincostFlowValue = sum((mincostFlow[u][7] for u in G.predecessors(7))) - sum(
+    ...     (mincostFlow[7][v] for v in G.successors(7))
+    ... )
+    >>> mincostFlowValue == nx.maximum_flow_value(G, 1, 7)
+    True
+
+    """
+    maxFlow = nx.maximum_flow_value(G, s, t, capacity=capacity)
+    H = nx.DiGraph(G)
+    H.add_node(s, demand=-maxFlow)
+    H.add_node(t, demand=maxFlow)
+    return min_cost_flow(H, capacity=capacity, weight=weight)

janus/lib/python3.10/site-packages/networkx/algorithms/flow/networksimplex.py

@@ -0,0 +1,666 @@
+"""
+Minimum cost flow algorithms on directed connected graphs.
+"""
+
+__all__ = ["network_simplex"]
+
+from itertools import chain, islice, repeat
+from math import ceil, sqrt
+
+import networkx as nx
+from networkx.utils import not_implemented_for
+
+
+class _DataEssentialsAndFunctions:
+    def __init__(
+        self, G, multigraph, demand="demand", capacity="capacity", weight="weight"
+    ):
+        # Number all nodes and edges and hereafter reference them using ONLY their numbers
+        self.node_list = list(G)  # nodes
+        self.node_indices = {u: i for i, u in enumerate(self.node_list)}  # node indices
+        self.node_demands = [
+            G.nodes[u].get(demand, 0) for u in self.node_list
+        ]  # node demands
+
+        self.edge_sources = []  # edge sources
+        self.edge_targets = []  # edge targets
+        if multigraph:
+            self.edge_keys = []  # edge keys
+        self.edge_indices = {}  # edge indices
+        self.edge_capacities = []  # edge capacities
+        self.edge_weights = []  # edge weights
+
+        if not multigraph:
+            edges = G.edges(data=True)
+        else:
+            edges = G.edges(data=True, keys=True)
+
+        inf = float("inf")
+        edges = (e for e in edges if e[0] != e[1] and e[-1].get(capacity, inf) != 0)
+        for i, e in enumerate(edges):
+            self.edge_sources.append(self.node_indices[e[0]])
+            self.edge_targets.append(self.node_indices[e[1]])
+            if multigraph:
+                self.edge_keys.append(e[2])
+            self.edge_indices[e[:-1]] = i
+            self.edge_capacities.append(e[-1].get(capacity, inf))
+            self.edge_weights.append(e[-1].get(weight, 0))
+
+        # spanning tree specific data to be initialized
+
+        self.edge_count = None  # number of edges
+        self.edge_flow = None  # edge flows
+        self.node_potentials = None  # node potentials
+        self.parent = None  # parent nodes
+        self.parent_edge = None  # edges to parents
+        self.subtree_size = None  # subtree sizes
+        self.next_node_dft = None  # next nodes in depth-first thread
+        self.prev_node_dft = None  # previous nodes in depth-first thread
+        self.last_descendent_dft = None  # last descendants in depth-first thread
+        self._spanning_tree_initialized = (
+            False  # False until initialize_spanning_tree() is called
+        )
+
+    def initialize_spanning_tree(self, n, faux_inf):
+        self.edge_count = len(self.edge_indices)  # number of edges
+        self.edge_flow = list(
+            chain(repeat(0, self.edge_count), (abs(d) for d in self.node_demands))
+        )  # edge flows
+        self.node_potentials = [
+            faux_inf if d <= 0 else -faux_inf for d in self.node_demands
+        ]  # node potentials
+        self.parent = list(chain(repeat(-1, n), [None]))  # parent nodes
+        self.parent_edge = list(
+            range(self.edge_count, self.edge_count + n)
+        )  # edges to parents
+        self.subtree_size = list(chain(repeat(1, n), [n + 1]))  # subtree sizes
+        self.next_node_dft = list(
+            chain(range(1, n), [-1, 0])
+        )  # next nodes in depth-first thread
+        self.prev_node_dft = list(range(-1, n))  # previous nodes in depth-first thread
+        self.last_descendent_dft = list(
+            chain(range(n), [n - 1])
+        )  # last descendants in depth-first thread
+        self._spanning_tree_initialized = True  # True only if all the assignments pass
+
+    def find_apex(self, p, q):
+        """
+        Find the lowest common ancestor of nodes p and q in the spanning tree.
+        """
+        size_p = self.subtree_size[p]
+        size_q = self.subtree_size[q]
+        while True:
+            while size_p < size_q:
+                p = self.parent[p]
+                size_p = self.subtree_size[p]
+            while size_p > size_q:
+                q = self.parent[q]
+                size_q = self.subtree_size[q]
+            if size_p == size_q:
+                if p != q:
+                    p = self.parent[p]
+                    size_p = self.subtree_size[p]
+                    q = self.parent[q]
+                    size_q = self.subtree_size[q]
+                else:
+                    return p
+
+    def trace_path(self, p, w):
+        """
+        Returns the nodes and edges on the path from node p to its ancestor w.
+        """
+        Wn = [p]
+        We = []
+        while p != w:
+            We.append(self.parent_edge[p])
+            p = self.parent[p]
+            Wn.append(p)
+        return Wn, We
+
+    def find_cycle(self, i, p, q):
+        """
+        Returns the nodes and edges on the cycle containing edge i == (p, q)
+        when the latter is added to the spanning tree.
+
+        The cycle is oriented in the direction from p to q.
+        """
+        w = self.find_apex(p, q)
+        Wn, We = self.trace_path(p, w)
+        Wn.reverse()
+        We.reverse()
+        if We != [i]:
+            We.append(i)
+        WnR, WeR = self.trace_path(q, w)
+        del WnR[-1]
+        Wn += WnR
+        We += WeR
+        return Wn, We
+
+    def augment_flow(self, Wn, We, f):
+        """
+        Augment f units of flow along a cycle represented by Wn and We.
+        """
+        for i, p in zip(We, Wn):
+            if self.edge_sources[i] == p:
+                self.edge_flow[i] += f
+            else:
+                self.edge_flow[i] -= f
+
+    def trace_subtree(self, p):
+        """
+        Yield the nodes in the subtree rooted at a node p.
+        """
+        yield p
+        l = self.last_descendent_dft[p]
+        while p != l:
+            p = self.next_node_dft[p]
+            yield p
+
+    def remove_edge(self, s, t):
+        """
+        Remove an edge (s, t) where parent[t] == s from the spanning tree.
+        """
+        size_t = self.subtree_size[t]
+        prev_t = self.prev_node_dft[t]
+        last_t = self.last_descendent_dft[t]
+        next_last_t = self.next_node_dft[last_t]
+        # Remove (s, t).
+        self.parent[t] = None
+        self.parent_edge[t] = None
+        # Remove the subtree rooted at t from the depth-first thread.
+        self.next_node_dft[prev_t] = next_last_t
+        self.prev_node_dft[next_last_t] = prev_t
+        self.next_node_dft[last_t] = t
+        self.prev_node_dft[t] = last_t
+        # Update the subtree sizes and last descendants of the (old) ancestors
+        # of t.
+        while s is not None:
+            self.subtree_size[s] -= size_t
+            if self.last_descendent_dft[s] == last_t:
+                self.last_descendent_dft[s] = prev_t
+            s = self.parent[s]
+
+    def make_root(self, q):
+        """
+        Make a node q the root of its containing subtree.
+        """
+        ancestors = []
+        while q is not None:
+            ancestors.append(q)
+            q = self.parent[q]
+        ancestors.reverse()
+        for p, q in zip(ancestors, islice(ancestors, 1, None)):
+            size_p = self.subtree_size[p]
+            last_p = self.last_descendent_dft[p]
+            prev_q = self.prev_node_dft[q]
+            last_q = self.last_descendent_dft[q]
+            next_last_q = self.next_node_dft[last_q]
+            # Make p a child of q.
+            self.parent[p] = q
+            self.parent[q] = None
+            self.parent_edge[p] = self.parent_edge[q]
+            self.parent_edge[q] = None
+            self.subtree_size[p] = size_p - self.subtree_size[q]
+            self.subtree_size[q] = size_p
+            # Remove the subtree rooted at q from the depth-first thread.
+            self.next_node_dft[prev_q] = next_last_q
+            self.prev_node_dft[next_last_q] = prev_q
+            self.next_node_dft[last_q] = q
+            self.prev_node_dft[q] = last_q
+            if last_p == last_q:
+                self.last_descendent_dft[p] = prev_q
+                last_p = prev_q
+            # Add the remaining parts of the subtree rooted at p as a subtree
+            # of q in the depth-first thread.
+            self.prev_node_dft[p] = last_q
+            self.next_node_dft[last_q] = p
+            self.next_node_dft[last_p] = q
+            self.prev_node_dft[q] = last_p
+            self.last_descendent_dft[q] = last_p
+
+    def add_edge(self, i, p, q):
+        """
+        Add an edge (p, q) to the spanning tree where q is the root of a subtree.
+        """
+        last_p = self.last_descendent_dft[p]
+        next_last_p = self.next_node_dft[last_p]
+        size_q = self.subtree_size[q]
+        last_q = self.last_descendent_dft[q]
+        # Make q a child of p.
+        self.parent[q] = p
+        self.parent_edge[q] = i
+        # Insert the subtree rooted at q into the depth-first thread.
+        self.next_node_dft[last_p] = q
+        self.prev_node_dft[q] = last_p
+        self.prev_node_dft[next_last_p] = last_q
+        self.next_node_dft[last_q] = next_last_p
+        # Update the subtree sizes and last descendants of the (new) ancestors
+        # of q.
+        while p is not None:
+            self.subtree_size[p] += size_q
+            if self.last_descendent_dft[p] == last_p:
+                self.last_descendent_dft[p] = last_q
+            p = self.parent[p]
+
+    def update_potentials(self, i, p, q):
+        """
+        Update the potentials of the nodes in the subtree rooted at a node
+        q connected to its parent p by an edge i.
+        """
+        if q == self.edge_targets[i]:
+            d = self.node_potentials[p] - self.edge_weights[i] - self.node_potentials[q]
+        else:
+            d = self.node_potentials[p] + self.edge_weights[i] - self.node_potentials[q]
+        for q in self.trace_subtree(q):
+            self.node_potentials[q] += d
+
+    def reduced_cost(self, i):
+        """Returns the reduced cost of an edge i."""
+        c = (
+            self.edge_weights[i]
+            - self.node_potentials[self.edge_sources[i]]
+            + self.node_potentials[self.edge_targets[i]]
+        )
+        return c if self.edge_flow[i] == 0 else -c
+
+    def find_entering_edges(self):
+        """Yield entering edges until none can be found."""
+        if self.edge_count == 0:
+            return
+
+        # Entering edges are found by combining Dantzig's rule and Bland's
+        # rule. The edges are cyclically grouped into blocks of size B. Within
+        # each block, Dantzig's rule is applied to find an entering edge. The
+        # blocks to search is determined following Bland's rule.
+        B = int(ceil(sqrt(self.edge_count)))  # pivot block size
+        M = (self.edge_count + B - 1) // B  # number of blocks needed to cover all edges
+        m = 0  # number of consecutive blocks without eligible
+        # entering edges
+        f = 0  # first edge in block
+        while m < M:
+            # Determine the next block of edges.
+            l = f + B
+            if l <= self.edge_count:
+                edges = range(f, l)
+            else:
+                l -= self.edge_count
+                edges = chain(range(f, self.edge_count), range(l))
+            f = l
+            # Find the first edge with the lowest reduced cost.
+            i = min(edges, key=self.reduced_cost)
+            c = self.reduced_cost(i)
+            if c >= 0:
+                # No entering edge found in the current block.
+                m += 1
+            else:
+                # Entering edge found.
+                if self.edge_flow[i] == 0:
+                    p = self.edge_sources[i]
+                    q = self.edge_targets[i]
+                else:
+                    p = self.edge_targets[i]
+                    q = self.edge_sources[i]
+                yield i, p, q
+                m = 0
+        # All edges have nonnegative reduced costs. The current flow is
+        # optimal.
+
+    def residual_capacity(self, i, p):
+        """Returns the residual capacity of an edge i in the direction away
+        from its endpoint p.
+        """
+        return (
+            self.edge_capacities[i] - self.edge_flow[i]
+            if self.edge_sources[i] == p
+            else self.edge_flow[i]
+        )
+
+    def find_leaving_edge(self, Wn, We):
+        """Returns the leaving edge in a cycle represented by Wn and We."""
+        j, s = min(
+            zip(reversed(We), reversed(Wn)),
+            key=lambda i_p: self.residual_capacity(*i_p),
+        )
+        t = self.edge_targets[j] if self.edge_sources[j] == s else self.edge_sources[j]
+        return j, s, t
+
+
+@not_implemented_for("undirected")
+@nx._dispatchable(
+    node_attrs="demand", edge_attrs={"capacity": float("inf"), "weight": 0}
+)
+def network_simplex(G, demand="demand", capacity="capacity", weight="weight"):
+    r"""Find a minimum cost flow satisfying all demands in digraph G.
+
+    This is a primal network simplex algorithm that uses the leaving
+    arc rule to prevent cycling.
+
+    G is a digraph with edge costs and capacities and in which nodes
+    have demand, i.e., they want to send or receive some amount of
+    flow. A negative demand means that the node wants to send flow, a
+    positive demand means that the node want to receive flow. A flow on
+    the digraph G satisfies all demand if the net flow into each node
+    is equal to the demand of that node.
+
+    Parameters
+    ----------
+    G : NetworkX graph
+        DiGraph on which a minimum cost flow satisfying all demands is
+        to be found.
+
+    demand : string
+        Nodes of the graph G are expected to have an attribute demand
+        that indicates how much flow a node wants to send (negative
+        demand) or receive (positive demand). Note that the sum of the
+        demands should be 0 otherwise the problem in not feasible. If
+        this attribute is not present, a node is considered to have 0
+        demand. Default value: 'demand'.
+
+    capacity : string
+        Edges of the graph G are expected to have an attribute capacity
+        that indicates how much flow the edge can support. If this
+        attribute is not present, the edge is considered to have
+        infinite capacity. Default value: 'capacity'.
+
+    weight : string
+        Edges of the graph G are expected to have an attribute weight
+        that indicates the cost incurred by sending one unit of flow on
+        that edge. If not present, the weight is considered to be 0.
+        Default value: 'weight'.
+
+    Returns
+    -------
+    flowCost : integer, float
+        Cost of a minimum cost flow satisfying all demands.
+
+    flowDict : dictionary
+        Dictionary of dictionaries keyed by nodes such that
+        flowDict[u][v] is the flow edge (u, v).
+
+    Raises
+    ------
+    NetworkXError
+        This exception is raised if the input graph is not directed or
+        not connected.
+
+    NetworkXUnfeasible
+        This exception is raised in the following situations:
+
+            * The sum of the demands is not zero. Then, there is no
+              flow satisfying all demands.
+            * There is no flow satisfying all demand.
+
+    NetworkXUnbounded
+        This exception is raised if the digraph G has a cycle of
+        negative cost and infinite capacity. Then, the cost of a flow
+        satisfying all demands is unbounded below.
+
+    Notes
+    -----
+    This algorithm is not guaranteed to work if edge weights or demands
+    are floating point numbers (overflows and roundoff errors can
+    cause problems). As a workaround you can use integer numbers by
+    multiplying the relevant edge attributes by a convenient
+    constant factor (eg 100).
+
+    See also
+    --------
+    cost_of_flow, max_flow_min_cost, min_cost_flow, min_cost_flow_cost
+
+    Examples
+    --------
+    A simple example of a min cost flow problem.
+
+    >>> G = nx.DiGraph()
+    >>> G.add_node("a", demand=-5)
+    >>> G.add_node("d", demand=5)
+    >>> G.add_edge("a", "b", weight=3, capacity=4)
+    >>> G.add_edge("a", "c", weight=6, capacity=10)
+    >>> G.add_edge("b", "d", weight=1, capacity=9)
+    >>> G.add_edge("c", "d", weight=2, capacity=5)
+    >>> flowCost, flowDict = nx.network_simplex(G)
+    >>> flowCost
+    24
+    >>> flowDict
+    {'a': {'b': 4, 'c': 1}, 'd': {}, 'b': {'d': 4}, 'c': {'d': 1}}
+
+    The mincost flow algorithm can also be used to solve shortest path
+    problems. To find the shortest path between two nodes u and v,
+    give all edges an infinite capacity, give node u a demand of -1 and
+    node v a demand a 1. Then run the network simplex. The value of a
+    min cost flow will be the distance between u and v and edges
+    carrying positive flow will indicate the path.
+
+    >>> G = nx.DiGraph()
+    >>> G.add_weighted_edges_from(
+    ...     [
+    ...         ("s", "u", 10),
+    ...         ("s", "x", 5),
+    ...         ("u", "v", 1),
+    ...         ("u", "x", 2),
+    ...         ("v", "y", 1),
+    ...         ("x", "u", 3),
+    ...         ("x", "v", 5),
+    ...         ("x", "y", 2),
+    ...         ("y", "s", 7),
+    ...         ("y", "v", 6),
+    ...     ]
+    ... )
+    >>> G.add_node("s", demand=-1)
+    >>> G.add_node("v", demand=1)
+    >>> flowCost, flowDict = nx.network_simplex(G)
+    >>> flowCost == nx.shortest_path_length(G, "s", "v", weight="weight")
+    True
+    >>> sorted([(u, v) for u in flowDict for v in flowDict[u] if flowDict[u][v] > 0])
+    [('s', 'x'), ('u', 'v'), ('x', 'u')]
+    >>> nx.shortest_path(G, "s", "v", weight="weight")
+    ['s', 'x', 'u', 'v']
+
+    It is possible to change the name of the attributes used for the
+    algorithm.
+
+    >>> G = nx.DiGraph()
+    >>> G.add_node("p", spam=-4)
+    >>> G.add_node("q", spam=2)
+    >>> G.add_node("a", spam=-2)
+    >>> G.add_node("d", spam=-1)
+    >>> G.add_node("t", spam=2)
+    >>> G.add_node("w", spam=3)
+    >>> G.add_edge("p", "q", cost=7, vacancies=5)
+    >>> G.add_edge("p", "a", cost=1, vacancies=4)
+    >>> G.add_edge("q", "d", cost=2, vacancies=3)
+    >>> G.add_edge("t", "q", cost=1, vacancies=2)
+    >>> G.add_edge("a", "t", cost=2, vacancies=4)
+    >>> G.add_edge("d", "w", cost=3, vacancies=4)
+    >>> G.add_edge("t", "w", cost=4, vacancies=1)
+    >>> flowCost, flowDict = nx.network_simplex(
+    ...     G, demand="spam", capacity="vacancies", weight="cost"
+    ... )
+    >>> flowCost
+    37
+    >>> flowDict
+    {'p': {'q': 2, 'a': 2}, 'q': {'d': 1}, 'a': {'t': 4}, 'd': {'w': 2}, 't': {'q': 1, 'w': 1}, 'w': {}}
+
+    References
+    ----------
+    .. [1] Z. Kiraly, P. Kovacs.
+           Efficient implementation of minimum-cost flow algorithms.
+           Acta Universitatis Sapientiae, Informatica 4(1):67--118. 2012.
+    .. [2] R. Barr, F. Glover, D. Klingman.
+           Enhancement of spanning tree labeling procedures for network
+           optimization.
+           INFOR 17(1):16--34. 1979.
+    """
+    ###########################################################################
+    # Problem essentials extraction and sanity check
+    ###########################################################################
+
+    if len(G) == 0:
+        raise nx.NetworkXError("graph has no nodes")
+
+    multigraph = G.is_multigraph()
+
+    # extracting data essential to problem
+    DEAF = _DataEssentialsAndFunctions(
+        G, multigraph, demand=demand, capacity=capacity, weight=weight
+    )
+
+    ###########################################################################
+    # Quick Error Detection
+    ###########################################################################
+
+    inf = float("inf")
+    for u, d in zip(DEAF.node_list, DEAF.node_demands):
+        if abs(d) == inf:
+            raise nx.NetworkXError(f"node {u!r} has infinite demand")
+    for e, w in zip(DEAF.edge_indices, DEAF.edge_weights):
+        if abs(w) == inf:
+            raise nx.NetworkXError(f"edge {e!r} has infinite weight")
+    if not multigraph:
+        edges = nx.selfloop_edges(G, data=True)
+    else:
+        edges = nx.selfloop_edges(G, data=True, keys=True)
+    for e in edges:
+        if abs(e[-1].get(weight, 0)) == inf:
+            raise nx.NetworkXError(f"edge {e[:-1]!r} has infinite weight")
+
+    ###########################################################################
+    # Quick Infeasibility Detection
+    ###########################################################################
+
+    if sum(DEAF.node_demands) != 0:
+        raise nx.NetworkXUnfeasible("total node demand is not zero")
+    for e, c in zip(DEAF.edge_indices, DEAF.edge_capacities):
+        if c < 0:
+            raise nx.NetworkXUnfeasible(f"edge {e!r} has negative capacity")
+    if not multigraph:
+        edges = nx.selfloop_edges(G, data=True)
+    else:
+        edges = nx.selfloop_edges(G, data=True, keys=True)
+    for e in edges:
+        if e[-1].get(capacity, inf) < 0:
+            raise nx.NetworkXUnfeasible(f"edge {e[:-1]!r} has negative capacity")
+
+    ###########################################################################
+    # Initialization
+    ###########################################################################
+
+    # Add a dummy node -1 and connect all existing nodes to it with infinite-
+    # capacity dummy edges. Node -1 will serve as the root of the
+    # spanning tree of the network simplex method. The new edges will used to
+    # trivially satisfy the node demands and create an initial strongly
+    # feasible spanning tree.
+    for i, d in enumerate(DEAF.node_demands):
+        # Must be greater-than here. Zero-demand nodes must have
+        # edges pointing towards the root to ensure strong feasibility.
+        if d > 0:
+            DEAF.edge_sources.append(-1)
+            DEAF.edge_targets.append(i)
+        else:
+            DEAF.edge_sources.append(i)
+            DEAF.edge_targets.append(-1)
+    faux_inf = (
+        3
+        * max(
+            chain(
+                [
+                    sum(c for c in DEAF.edge_capacities if c < inf),
+                    sum(abs(w) for w in DEAF.edge_weights),
+                ],
+                (abs(d) for d in DEAF.node_demands),
+            )
+        )
+        or 1
+    )
+
+    n = len(DEAF.node_list)  # number of nodes
+    DEAF.edge_weights.extend(repeat(faux_inf, n))
+    DEAF.edge_capacities.extend(repeat(faux_inf, n))
+
+    # Construct the initial spanning tree.
+    DEAF.initialize_spanning_tree(n, faux_inf)
+
+    ###########################################################################
+    # Pivot loop
+    ###########################################################################
+
+    for i, p, q in DEAF.find_entering_edges():
+        Wn, We = DEAF.find_cycle(i, p, q)
+        j, s, t = DEAF.find_leaving_edge(Wn, We)
+        DEAF.augment_flow(Wn, We, DEAF.residual_capacity(j, s))
+        # Do nothing more if the entering edge is the same as the leaving edge.
+        if i != j:
+            if DEAF.parent[t] != s:
+                # Ensure that s is the parent of t.
+                s, t = t, s
+            if We.index(i) > We.index(j):
+                # Ensure that q is in the subtree rooted at t.
+                p, q = q, p
+            DEAF.remove_edge(s, t)
+            DEAF.make_root(q)
+            DEAF.add_edge(i, p, q)
+            DEAF.update_potentials(i, p, q)
+
+    ###########################################################################
+    # Infeasibility and unboundedness detection
+    ###########################################################################
+
+    if any(DEAF.edge_flow[i] != 0 for i in range(-n, 0)):
+        raise nx.NetworkXUnfeasible("no flow satisfies all node demands")
+
+    if any(DEAF.edge_flow[i] * 2 >= faux_inf for i in range(DEAF.edge_count)) or any(
+        e[-1].get(capacity, inf) == inf and e[-1].get(weight, 0) < 0
+        for e in nx.selfloop_edges(G, data=True)
+    ):
+        raise nx.NetworkXUnbounded("negative cycle with infinite capacity found")
+
+    ###########################################################################
+    # Flow cost calculation and flow dict construction
+    ###########################################################################
+
+    del DEAF.edge_flow[DEAF.edge_count :]
+    flow_cost = sum(w * x for w, x in zip(DEAF.edge_weights, DEAF.edge_flow))
+    flow_dict = {n: {} for n in DEAF.node_list}
+
+    def add_entry(e):
+        """Add a flow dict entry."""
+        d = flow_dict[e[0]]
+        for k in e[1:-2]:
+            try:
+                d = d[k]
+            except KeyError:
+                t = {}
+                d[k] = t
+                d = t
+        d[e[-2]] = e[-1]
+
+    DEAF.edge_sources = (
+        DEAF.node_list[s] for s in DEAF.edge_sources
+    )  # Use original nodes.
+    DEAF.edge_targets = (
+        DEAF.node_list[t] for t in DEAF.edge_targets
+    )  # Use original nodes.
+    if not multigraph:
+        for e in zip(DEAF.edge_sources, DEAF.edge_targets, DEAF.edge_flow):
+            add_entry(e)
+        edges = G.edges(data=True)
+    else:
+        for e in zip(
+            DEAF.edge_sources, DEAF.edge_targets, DEAF.edge_keys, DEAF.edge_flow
+        ):
+            add_entry(e)
+        edges = G.edges(data=True, keys=True)
+    for e in edges:
+        if e[0] != e[1]:
+            if e[-1].get(capacity, inf) == 0:
+                add_entry(e[:-1] + (0,))
+        else:
+            w = e[-1].get(weight, 0)
+            if w >= 0:
+                add_entry(e[:-1] + (0,))
+            else:
+                c = e[-1][capacity]
+                flow_cost += w * c
+                add_entry(e[:-1] + (c,))
+
+    return flow_cost, flow_dict

janus/lib/python3.10/site-packages/networkx/algorithms/flow/preflowpush.py

@@ -0,0 +1,425 @@
+"""
+Highest-label preflow-push algorithm for maximum flow problems.
+"""
+
+from collections import deque
+from itertools import islice
+
+import networkx as nx
+
+from ...utils import arbitrary_element
+from .utils import (
+    CurrentEdge,
+    GlobalRelabelThreshold,
+    Level,
+    build_residual_network,
+    detect_unboundedness,
+)
+
+__all__ = ["preflow_push"]
+
+
+def preflow_push_impl(G, s, t, capacity, residual, global_relabel_freq, value_only):
+    """Implementation of the highest-label preflow-push algorithm."""
+    if s not in G:
+        raise nx.NetworkXError(f"node {str(s)} not in graph")
+    if t not in G:
+        raise nx.NetworkXError(f"node {str(t)} not in graph")
+    if s == t:
+        raise nx.NetworkXError("source and sink are the same node")
+
+    if global_relabel_freq is None:
+        global_relabel_freq = 0
+    if global_relabel_freq < 0:
+        raise nx.NetworkXError("global_relabel_freq must be nonnegative.")
+
+    if residual is None:
+        R = build_residual_network(G, capacity)
+    else:
+        R = residual
+
+    detect_unboundedness(R, s, t)
+
+    R_nodes = R.nodes
+    R_pred = R.pred
+    R_succ = R.succ
+
+    # Initialize/reset the residual network.
+    for u in R:
+        R_nodes[u]["excess"] = 0
+        for e in R_succ[u].values():
+            e["flow"] = 0
+
+    def reverse_bfs(src):
+        """Perform a reverse breadth-first search from src in the residual
+        network.
+        """
+        heights = {src: 0}
+        q = deque([(src, 0)])
+        while q:
+            u, height = q.popleft()
+            height += 1
+            for v, attr in R_pred[u].items():
+                if v not in heights and attr["flow"] < attr["capacity"]:
+                    heights[v] = height
+                    q.append((v, height))
+        return heights
+
+    # Initialize heights of the nodes.
+    heights = reverse_bfs(t)
+
+    if s not in heights:
+        # t is not reachable from s in the residual network. The maximum flow
+        # must be zero.
+        R.graph["flow_value"] = 0
+        return R
+
+    n = len(R)
+    # max_height represents the height of the highest level below level n with
+    # at least one active node.
+    max_height = max(heights[u] for u in heights if u != s)
+    heights[s] = n
+
+    grt = GlobalRelabelThreshold(n, R.size(), global_relabel_freq)
+
+    # Initialize heights and 'current edge' data structures of the nodes.
+    for u in R:
+        R_nodes[u]["height"] = heights[u] if u in heights else n + 1
+        R_nodes[u]["curr_edge"] = CurrentEdge(R_succ[u])
+
+    def push(u, v, flow):
+        """Push flow units of flow from u to v."""
+        R_succ[u][v]["flow"] += flow
+        R_succ[v][u]["flow"] -= flow
+        R_nodes[u]["excess"] -= flow
+        R_nodes[v]["excess"] += flow
+
+    # The maximum flow must be nonzero now. Initialize the preflow by
+    # saturating all edges emanating from s.
+    for u, attr in R_succ[s].items():
+        flow = attr["capacity"]
+        if flow > 0:
+            push(s, u, flow)
+
+    # Partition nodes into levels.
+    levels = [Level() for i in range(2 * n)]
+    for u in R:
+        if u != s and u != t:
+            level = levels[R_nodes[u]["height"]]
+            if R_nodes[u]["excess"] > 0:
+                level.active.add(u)
+            else:
+                level.inactive.add(u)
+
+    def activate(v):
+        """Move a node from the inactive set to the active set of its level."""
+        if v != s and v != t:
+            level = levels[R_nodes[v]["height"]]
+            if v in level.inactive:
+                level.inactive.remove(v)
+                level.active.add(v)
+
+    def relabel(u):
+        """Relabel a node to create an admissible edge."""
+        grt.add_work(len(R_succ[u]))
+        return (
+            min(
+                R_nodes[v]["height"]
+                for v, attr in R_succ[u].items()
+                if attr["flow"] < attr["capacity"]
+            )
+            + 1
+        )
+
+    def discharge(u, is_phase1):
+        """Discharge a node until it becomes inactive or, during phase 1 (see
+        below), its height reaches at least n. The node is known to have the
+        largest height among active nodes.
+        """
+        height = R_nodes[u]["height"]
+        curr_edge = R_nodes[u]["curr_edge"]
+        # next_height represents the next height to examine after discharging
+        # the current node. During phase 1, it is capped to below n.
+        next_height = height
+        levels[height].active.remove(u)
+        while True:
+            v, attr = curr_edge.get()
+            if height == R_nodes[v]["height"] + 1 and attr["flow"] < attr["capacity"]:
+                flow = min(R_nodes[u]["excess"], attr["capacity"] - attr["flow"])
+                push(u, v, flow)
+                activate(v)
+                if R_nodes[u]["excess"] == 0:
+                    # The node has become inactive.
+                    levels[height].inactive.add(u)
+                    break
+            try:
+                curr_edge.move_to_next()
+            except StopIteration:
+                # We have run off the end of the adjacency list, and there can
+                # be no more admissible edges. Relabel the node to create one.
+                height = relabel(u)
+                if is_phase1 and height >= n - 1:
+                    # Although the node is still active, with a height at least
+                    # n - 1, it is now known to be on the s side of the minimum
+                    # s-t cut. Stop processing it until phase 2.
+                    levels[height].active.add(u)
+                    break
+                # The first relabel operation after global relabeling may not
+                # increase the height of the node since the 'current edge' data
+                # structure is not rewound. Use height instead of (height - 1)
+                # in case other active nodes at the same level are missed.
+                next_height = height
+        R_nodes[u]["height"] = height
+        return next_height
+
+    def gap_heuristic(height):
+        """Apply the gap heuristic."""
+        # Move all nodes at levels (height + 1) to max_height to level n + 1.
+        for level in islice(levels, height + 1, max_height + 1):
+            for u in level.active:
+                R_nodes[u]["height"] = n + 1
+            for u in level.inactive:
+                R_nodes[u]["height"] = n + 1
+            levels[n + 1].active.update(level.active)
+            level.active.clear()
+            levels[n + 1].inactive.update(level.inactive)
+            level.inactive.clear()
+
+    def global_relabel(from_sink):
+        """Apply the global relabeling heuristic."""
+        src = t if from_sink else s
+        heights = reverse_bfs(src)
+        if not from_sink:
+            # s must be reachable from t. Remove t explicitly.
+            del heights[t]
+        max_height = max(heights.values())
+        if from_sink:
+            # Also mark nodes from which t is unreachable for relabeling. This
+            # serves the same purpose as the gap heuristic.
+            for u in R:
+                if u not in heights and R_nodes[u]["height"] < n:
+                    heights[u] = n + 1
+        else:
+            # Shift the computed heights because the height of s is n.
+            for u in heights:
+                heights[u] += n
+            max_height += n
+        del heights[src]
+        for u, new_height in heights.items():
+            old_height = R_nodes[u]["height"]
+            if new_height != old_height:
+                if u in levels[old_height].active:
+                    levels[old_height].active.remove(u)
+                    levels[new_height].active.add(u)
+                else:
+                    levels[old_height].inactive.remove(u)
+                    levels[new_height].inactive.add(u)
+                R_nodes[u]["height"] = new_height
+        return max_height
+
+    # Phase 1: Find the maximum preflow by pushing as much flow as possible to
+    # t.
+
+    height = max_height
+    while height > 0:
+        # Discharge active nodes in the current level.
+        while True:
+            level = levels[height]
+            if not level.active:
+                # All active nodes in the current level have been discharged.
+                # Move to the next lower level.
+                height -= 1
+                break
+            # Record the old height and level for the gap heuristic.
+            old_height = height
+            old_level = level
+            u = arbitrary_element(level.active)
+            height = discharge(u, True)
+            if grt.is_reached():
+                # Global relabeling heuristic: Recompute the exact heights of
+                # all nodes.
+                height = global_relabel(True)
+                max_height = height
+                grt.clear_work()
+            elif not old_level.active and not old_level.inactive:
+                # Gap heuristic: If the level at old_height is empty (a 'gap'),
+                # a minimum cut has been identified. All nodes with heights
+                # above old_height can have their heights set to n + 1 and not
+                # be further processed before a maximum preflow is found.
+                gap_heuristic(old_height)
+                height = old_height - 1
+                max_height = height
+            else:
+                # Update the height of the highest level with at least one
+                # active node.
+                max_height = max(max_height, height)
+
+    # A maximum preflow has been found. The excess at t is the maximum flow
+    # value.
+    if value_only:
+        R.graph["flow_value"] = R_nodes[t]["excess"]
+        return R
+
+    # Phase 2: Convert the maximum preflow into a maximum flow by returning the
+    # excess to s.
+
+    # Relabel all nodes so that they have accurate heights.
+    height = global_relabel(False)
+    grt.clear_work()
+
+    # Continue to discharge the active nodes.
+    while height > n:
+        # Discharge active nodes in the current level.
+        while True:
+            level = levels[height]
+            if not level.active:
+                # All active nodes in the current level have been discharged.
+                # Move to the next lower level.
+                height -= 1
+                break
+            u = arbitrary_element(level.active)
+            height = discharge(u, False)
+            if grt.is_reached():
+                # Global relabeling heuristic.
+                height = global_relabel(False)
+                grt.clear_work()
+
+    R.graph["flow_value"] = R_nodes[t]["excess"]
+    return R
+
+
+@nx._dispatchable(edge_attrs={"capacity": float("inf")}, returns_graph=True)
+def preflow_push(
+    G, s, t, capacity="capacity", residual=None, global_relabel_freq=1, value_only=False
+):
+    r"""Find a maximum single-commodity flow using the highest-label
+    preflow-push algorithm.
+
+    This function returns the residual network resulting after computing
+    the maximum flow. See below for details about the conventions
+    NetworkX uses for defining residual networks.
+
+    This algorithm has a running time of $O(n^2 \sqrt{m})$ for $n$ nodes and
+    $m$ edges.
+
+
+    Parameters
+    ----------
+    G : NetworkX graph
+        Edges of the graph are expected to have an attribute called
+        'capacity'. If this attribute is not present, the edge is
+        considered to have infinite capacity.
+
+    s : node
+        Source node for the flow.
+
+    t : node
+        Sink node for the flow.
+
+    capacity : string
+        Edges of the graph G are expected to have an attribute capacity
+        that indicates how much flow the edge can support. If this
+        attribute is not present, the edge is considered to have
+        infinite capacity. Default value: 'capacity'.
+
+    residual : NetworkX graph
+        Residual network on which the algorithm is to be executed. If None, a
+        new residual network is created. Default value: None.
+
+    global_relabel_freq : integer, float
+        Relative frequency of applying the global relabeling heuristic to speed
+        up the algorithm. If it is None, the heuristic is disabled. Default
+        value: 1.
+
+    value_only : bool
+        If False, compute a maximum flow; otherwise, compute a maximum preflow
+        which is enough for computing the maximum flow value. Default value:
+        False.
+
+    Returns
+    -------
+    R : NetworkX DiGraph
+        Residual network after computing the maximum flow.
+
+    Raises
+    ------
+    NetworkXError
+        The algorithm does not support MultiGraph and MultiDiGraph. If
+        the input graph is an instance of one of these two classes, a
+        NetworkXError is raised.
+
+    NetworkXUnbounded
+        If the graph has a path of infinite capacity, the value of a
+        feasible flow on the graph is unbounded above and the function
+        raises a NetworkXUnbounded.
+
+    See also
+    --------
+    :meth:`maximum_flow`
+    :meth:`minimum_cut`
+    :meth:`edmonds_karp`
+    :meth:`shortest_augmenting_path`
+
+    Notes
+    -----
+    The residual network :samp:`R` from an input graph :samp:`G` has the
+    same nodes as :samp:`G`. :samp:`R` is a DiGraph that contains a pair
+    of edges :samp:`(u, v)` and :samp:`(v, u)` iff :samp:`(u, v)` is not a
+    self-loop, and at least one of :samp:`(u, v)` and :samp:`(v, u)` exists
+    in :samp:`G`. For each node :samp:`u` in :samp:`R`,
+    :samp:`R.nodes[u]['excess']` represents the difference between flow into
+    :samp:`u` and flow out of :samp:`u`.
+
+    For each edge :samp:`(u, v)` in :samp:`R`, :samp:`R[u][v]['capacity']`
+    is equal to the capacity of :samp:`(u, v)` in :samp:`G` if it exists
+    in :samp:`G` or zero otherwise. If the capacity is infinite,
+    :samp:`R[u][v]['capacity']` will have a high arbitrary finite value
+    that does not affect the solution of the problem. This value is stored in
+    :samp:`R.graph['inf']`. For each edge :samp:`(u, v)` in :samp:`R`,
+    :samp:`R[u][v]['flow']` represents the flow function of :samp:`(u, v)` and
+    satisfies :samp:`R[u][v]['flow'] == -R[v][u]['flow']`.
+
+    The flow value, defined as the total flow into :samp:`t`, the sink, is
+    stored in :samp:`R.graph['flow_value']`. Reachability to :samp:`t` using
+    only edges :samp:`(u, v)` such that
+    :samp:`R[u][v]['flow'] < R[u][v]['capacity']` induces a minimum
+    :samp:`s`-:samp:`t` cut.
+
+    Examples
+    --------
+    >>> from networkx.algorithms.flow import preflow_push
+
+    The functions that implement flow algorithms and output a residual
+    network, such as this one, are not imported to the base NetworkX
+    namespace, so you have to explicitly import them from the flow package.
+
+    >>> G = nx.DiGraph()
+    >>> G.add_edge("x", "a", capacity=3.0)
+    >>> G.add_edge("x", "b", capacity=1.0)
+    >>> G.add_edge("a", "c", capacity=3.0)
+    >>> G.add_edge("b", "c", capacity=5.0)
+    >>> G.add_edge("b", "d", capacity=4.0)
+    >>> G.add_edge("d", "e", capacity=2.0)
+    >>> G.add_edge("c", "y", capacity=2.0)
+    >>> G.add_edge("e", "y", capacity=3.0)
+    >>> R = preflow_push(G, "x", "y")
+    >>> flow_value = nx.maximum_flow_value(G, "x", "y")
+    >>> flow_value == R.graph["flow_value"]
+    True
+    >>> # preflow_push also stores the maximum flow value
+    >>> # in the excess attribute of the sink node t
+    >>> flow_value == R.nodes["y"]["excess"]
+    True
+    >>> # For some problems, you might only want to compute a
+    >>> # maximum preflow.
+    >>> R = preflow_push(G, "x", "y", value_only=True)
+    >>> flow_value == R.graph["flow_value"]
+    True
+    >>> flow_value == R.nodes["y"]["excess"]
+    True
+
+    """
+    R = preflow_push_impl(G, s, t, capacity, residual, global_relabel_freq, value_only)
+    R.graph["algorithm"] = "preflow_push"
+    nx._clear_cache(R)
+    return R

janus/lib/python3.10/site-packages/networkx/algorithms/flow/tests/test_gomory_hu.py

@@ -0,0 +1,128 @@
+from itertools import combinations
+
+import pytest
+
+import networkx as nx
+from networkx.algorithms.flow import (
+    boykov_kolmogorov,
+    dinitz,
+    edmonds_karp,
+    preflow_push,
+    shortest_augmenting_path,
+)
+
+flow_funcs = [
+    boykov_kolmogorov,
+    dinitz,
+    edmonds_karp,
+    preflow_push,
+    shortest_augmenting_path,
+]
+
+
+class TestGomoryHuTree:
+    def minimum_edge_weight(self, T, u, v):
+        path = nx.shortest_path(T, u, v, weight="weight")
+        return min((T[u][v]["weight"], (u, v)) for (u, v) in zip(path, path[1:]))
+
+    def compute_cutset(self, G, T_orig, edge):
+        T = T_orig.copy()
+        T.remove_edge(*edge)
+        U, V = list(nx.connected_components(T))
+        cutset = set()
+        for x, nbrs in ((n, G[n]) for n in U):
+            cutset.update((x, y) for y in nbrs if y in V)
+        return cutset
+
+    def test_default_flow_function_karate_club_graph(self):
+        G = nx.karate_club_graph()
+        nx.set_edge_attributes(G, 1, "capacity")
+        T = nx.gomory_hu_tree(G)
+        assert nx.is_tree(T)
+        for u, v in combinations(G, 2):
+            cut_value, edge = self.minimum_edge_weight(T, u, v)
+            assert nx.minimum_cut_value(G, u, v) == cut_value
+
+    def test_karate_club_graph(self):
+        G = nx.karate_club_graph()
+        nx.set_edge_attributes(G, 1, "capacity")
+        for flow_func in flow_funcs:
+            T = nx.gomory_hu_tree(G, flow_func=flow_func)
+            assert nx.is_tree(T)
+            for u, v in combinations(G, 2):
+                cut_value, edge = self.minimum_edge_weight(T, u, v)
+                assert nx.minimum_cut_value(G, u, v) == cut_value
+
+    def test_davis_southern_women_graph(self):
+        G = nx.davis_southern_women_graph()
+        nx.set_edge_attributes(G, 1, "capacity")
+        for flow_func in flow_funcs:
+            T = nx.gomory_hu_tree(G, flow_func=flow_func)
+            assert nx.is_tree(T)
+            for u, v in combinations(G, 2):
+                cut_value, edge = self.minimum_edge_weight(T, u, v)
+                assert nx.minimum_cut_value(G, u, v) == cut_value
+
+    def test_florentine_families_graph(self):
+        G = nx.florentine_families_graph()
+        nx.set_edge_attributes(G, 1, "capacity")
+        for flow_func in flow_funcs:
+            T = nx.gomory_hu_tree(G, flow_func=flow_func)
+            assert nx.is_tree(T)
+            for u, v in combinations(G, 2):
+                cut_value, edge = self.minimum_edge_weight(T, u, v)
+                assert nx.minimum_cut_value(G, u, v) == cut_value
+
+    @pytest.mark.slow
+    def test_les_miserables_graph_cutset(self):
+        G = nx.les_miserables_graph()
+        nx.set_edge_attributes(G, 1, "capacity")
+        for flow_func in flow_funcs:
+            T = nx.gomory_hu_tree(G, flow_func=flow_func)
+            assert nx.is_tree(T)
+            for u, v in combinations(G, 2):
+                cut_value, edge = self.minimum_edge_weight(T, u, v)
+                assert nx.minimum_cut_value(G, u, v) == cut_value
+
+    def test_karate_club_graph_cutset(self):
+        G = nx.karate_club_graph()
+        nx.set_edge_attributes(G, 1, "capacity")
+        T = nx.gomory_hu_tree(G)
+        assert nx.is_tree(T)
+        u, v = 0, 33
+        cut_value, edge = self.minimum_edge_weight(T, u, v)
+        cutset = self.compute_cutset(G, T, edge)
+        assert cut_value == len(cutset)
+
+    def test_wikipedia_example(self):
+        # Example from https://en.wikipedia.org/wiki/Gomory%E2%80%93Hu_tree
+        G = nx.Graph()
+        G.add_weighted_edges_from(
+            (
+                (0, 1, 1),
+                (0, 2, 7),
+                (1, 2, 1),
+                (1, 3, 3),
+                (1, 4, 2),
+                (2, 4, 4),
+                (3, 4, 1),
+                (3, 5, 6),
+                (4, 5, 2),
+            )
+        )
+        for flow_func in flow_funcs:
+            T = nx.gomory_hu_tree(G, capacity="weight", flow_func=flow_func)
+            assert nx.is_tree(T)
+            for u, v in combinations(G, 2):
+                cut_value, edge = self.minimum_edge_weight(T, u, v)
+                assert nx.minimum_cut_value(G, u, v, capacity="weight") == cut_value
+
+    def test_directed_raises(self):
+        with pytest.raises(nx.NetworkXNotImplemented):
+            G = nx.DiGraph()
+            T = nx.gomory_hu_tree(G)
+
+    def test_empty_raises(self):
+        with pytest.raises(nx.NetworkXError):
+            G = nx.empty_graph()
+            T = nx.gomory_hu_tree(G)

janus/lib/python3.10/site-packages/networkx/algorithms/flow/tests/test_maxflow.py

@@ -0,0 +1,573 @@
+"""Maximum flow algorithms test suite."""
+
+import pytest
+
+import networkx as nx
+from networkx.algorithms.flow import (
+    boykov_kolmogorov,
+    build_flow_dict,
+    build_residual_network,
+    dinitz,
+    edmonds_karp,
+    preflow_push,
+    shortest_augmenting_path,
+)
+
+flow_funcs = {
+    boykov_kolmogorov,
+    dinitz,
+    edmonds_karp,
+    preflow_push,
+    shortest_augmenting_path,
+}
+
+max_min_funcs = {nx.maximum_flow, nx.minimum_cut}
+flow_value_funcs = {nx.maximum_flow_value, nx.minimum_cut_value}
+interface_funcs = max_min_funcs | flow_value_funcs
+all_funcs = flow_funcs | interface_funcs
+
+
+def compute_cutset(G, partition):
+    reachable, non_reachable = partition
+    cutset = set()
+    for u, nbrs in ((n, G[n]) for n in reachable):
+        cutset.update((u, v) for v in nbrs if v in non_reachable)
+    return cutset
+
+
+def validate_flows(G, s, t, flowDict, solnValue, capacity, flow_func):
+    errmsg = f"Assertion failed in function: {flow_func.__name__}"
+    assert set(G) == set(flowDict), errmsg
+    for u in G:
+        assert set(G[u]) == set(flowDict[u]), errmsg
+    excess = {u: 0 for u in flowDict}
+    for u in flowDict:
+        for v, flow in flowDict[u].items():
+            if capacity in G[u][v]:
+                assert flow <= G[u][v][capacity]
+            assert flow >= 0, errmsg
+            excess[u] -= flow
+            excess[v] += flow
+    for u, exc in excess.items():
+        if u == s:
+            assert exc == -solnValue, errmsg
+        elif u == t:
+            assert exc == solnValue, errmsg
+        else:
+            assert exc == 0, errmsg
+
+
+def validate_cuts(G, s, t, solnValue, partition, capacity, flow_func):
+    errmsg = f"Assertion failed in function: {flow_func.__name__}"
+    assert all(n in G for n in partition[0]), errmsg
+    assert all(n in G for n in partition[1]), errmsg
+    cutset = compute_cutset(G, partition)
+    assert all(G.has_edge(u, v) for (u, v) in cutset), errmsg
+    assert solnValue == sum(G[u][v][capacity] for (u, v) in cutset), errmsg
+    H = G.copy()
+    H.remove_edges_from(cutset)
+    if not G.is_directed():
+        assert not nx.is_connected(H), errmsg
+    else:
+        assert not nx.is_strongly_connected(H), errmsg
+
+
+def compare_flows_and_cuts(G, s, t, solnValue, capacity="capacity"):
+    for flow_func in flow_funcs:
+        errmsg = f"Assertion failed in function: {flow_func.__name__}"
+        R = flow_func(G, s, t, capacity)
+        # Test both legacy and new implementations.
+        flow_value = R.graph["flow_value"]
+        flow_dict = build_flow_dict(G, R)
+        assert flow_value == solnValue, errmsg
+        validate_flows(G, s, t, flow_dict, solnValue, capacity, flow_func)
+        # Minimum cut
+        cut_value, partition = nx.minimum_cut(
+            G, s, t, capacity=capacity, flow_func=flow_func
+        )
+        validate_cuts(G, s, t, solnValue, partition, capacity, flow_func)
+
+
+class TestMaxflowMinCutCommon:
+    def test_graph1(self):
+        # Trivial undirected graph
+        G = nx.Graph()
+        G.add_edge(1, 2, capacity=1.0)
+
+        # solution flows
+        # {1: {2: 1.0}, 2: {1: 1.0}}
+
+        compare_flows_and_cuts(G, 1, 2, 1.0)
+
+    def test_graph2(self):
+        # A more complex undirected graph
+        # adapted from https://web.archive.org/web/20220815055650/https://www.topcoder.com/thrive/articles/Maximum%20Flow:%20Part%20One
+        G = nx.Graph()
+        G.add_edge("x", "a", capacity=3.0)
+        G.add_edge("x", "b", capacity=1.0)
+        G.add_edge("a", "c", capacity=3.0)
+        G.add_edge("b", "c", capacity=5.0)
+        G.add_edge("b", "d", capacity=4.0)
+        G.add_edge("d", "e", capacity=2.0)
+        G.add_edge("c", "y", capacity=2.0)
+        G.add_edge("e", "y", capacity=3.0)
+
+        # H
+        # {
+        #     "x": {"a": 3, "b": 1},
+        #     "a": {"c": 3, "x": 3},
+        #     "b": {"c": 1, "d": 2, "x": 1},
+        #     "c": {"a": 3, "b": 1, "y": 2},
+        #     "d": {"b": 2, "e": 2},
+        #     "e": {"d": 2, "y": 2},
+        #     "y": {"c": 2, "e": 2},
+        # }
+
+        compare_flows_and_cuts(G, "x", "y", 4.0)
+
+    def test_digraph1(self):
+        # The classic directed graph example
+        G = nx.DiGraph()
+        G.add_edge("a", "b", capacity=1000.0)
+        G.add_edge("a", "c", capacity=1000.0)
+        G.add_edge("b", "c", capacity=1.0)
+        G.add_edge("b", "d", capacity=1000.0)
+        G.add_edge("c", "d", capacity=1000.0)
+
+        # H
+        # {
+        #     "a": {"b": 1000.0, "c": 1000.0},
+        #     "b": {"c": 0, "d": 1000.0},
+        #     "c": {"d": 1000.0},
+        #     "d": {},
+        # }
+
+        compare_flows_and_cuts(G, "a", "d", 2000.0)
+
+    def test_digraph2(self):
+        # An example in which some edges end up with zero flow.
+        G = nx.DiGraph()
+        G.add_edge("s", "b", capacity=2)
+        G.add_edge("s", "c", capacity=1)
+        G.add_edge("c", "d", capacity=1)
+        G.add_edge("d", "a", capacity=1)
+        G.add_edge("b", "a", capacity=2)
+        G.add_edge("a", "t", capacity=2)
+
+        # H
+        # {
+        #     "s": {"b": 2, "c": 0},
+        #     "c": {"d": 0},
+        #     "d": {"a": 0},
+        #     "b": {"a": 2},
+        #     "a": {"t": 2},
+        #     "t": {},
+        # }
+
+        compare_flows_and_cuts(G, "s", "t", 2)
+
+    def test_digraph3(self):
+        # A directed graph example from Cormen et al.
+        G = nx.DiGraph()
+        G.add_edge("s", "v1", capacity=16.0)
+        G.add_edge("s", "v2", capacity=13.0)
+        G.add_edge("v1", "v2", capacity=10.0)
+        G.add_edge("v2", "v1", capacity=4.0)
+        G.add_edge("v1", "v3", capacity=12.0)
+        G.add_edge("v3", "v2", capacity=9.0)
+        G.add_edge("v2", "v4", capacity=14.0)
+        G.add_edge("v4", "v3", capacity=7.0)
+        G.add_edge("v3", "t", capacity=20.0)
+        G.add_edge("v4", "t", capacity=4.0)
+
+        # H
+        # {
+        #     "s": {"v1": 12.0, "v2": 11.0},
+        #     "v2": {"v1": 0, "v4": 11.0},
+        #     "v1": {"v2": 0, "v3": 12.0},
+        #     "v3": {"v2": 0, "t": 19.0},
+        #     "v4": {"v3": 7.0, "t": 4.0},
+        #     "t": {},
+        # }
+
+        compare_flows_and_cuts(G, "s", "t", 23.0)
+
+    def test_digraph4(self):
+        # A more complex directed graph
+        # from https://web.archive.org/web/20220815055650/https://www.topcoder.com/thrive/articles/Maximum%20Flow:%20Part%20One
+        G = nx.DiGraph()
+        G.add_edge("x", "a", capacity=3.0)
+        G.add_edge("x", "b", capacity=1.0)
+        G.add_edge("a", "c", capacity=3.0)
+        G.add_edge("b", "c", capacity=5.0)
+        G.add_edge("b", "d", capacity=4.0)
+        G.add_edge("d", "e", capacity=2.0)
+        G.add_edge("c", "y", capacity=2.0)
+        G.add_edge("e", "y", capacity=3.0)
+
+        # H
+        # {
+        #     "x": {"a": 2.0, "b": 1.0},
+        #     "a": {"c": 2.0},
+        #     "b": {"c": 0, "d": 1.0},
+        #     "c": {"y": 2.0},
+        #     "d": {"e": 1.0},
+        #     "e": {"y": 1.0},
+        #     "y": {},
+        # }
+
+        compare_flows_and_cuts(G, "x", "y", 3.0)
+
+    def test_wikipedia_dinitz_example(self):
+        # Nice example from https://en.wikipedia.org/wiki/Dinic's_algorithm
+        G = nx.DiGraph()
+        G.add_edge("s", 1, capacity=10)
+        G.add_edge("s", 2, capacity=10)
+        G.add_edge(1, 3, capacity=4)
+        G.add_edge(1, 4, capacity=8)
+        G.add_edge(1, 2, capacity=2)
+        G.add_edge(2, 4, capacity=9)
+        G.add_edge(3, "t", capacity=10)
+        G.add_edge(4, 3, capacity=6)
+        G.add_edge(4, "t", capacity=10)
+
+        # solution flows
+        # {
+        #     1: {2: 0, 3: 4, 4: 6},
+        #     2: {4: 9},
+        #     3: {"t": 9},
+        #     4: {3: 5, "t": 10},
+        #     "s": {1: 10, 2: 9},
+        #     "t": {},
+        # }
+
+        compare_flows_and_cuts(G, "s", "t", 19)
+
+    def test_optional_capacity(self):
+        # Test optional capacity parameter.
+        G = nx.DiGraph()
+        G.add_edge("x", "a", spam=3.0)
+        G.add_edge("x", "b", spam=1.0)
+        G.add_edge("a", "c", spam=3.0)
+        G.add_edge("b", "c", spam=5.0)
+        G.add_edge("b", "d", spam=4.0)
+        G.add_edge("d", "e", spam=2.0)
+        G.add_edge("c", "y", spam=2.0)
+        G.add_edge("e", "y", spam=3.0)
+
+        # solution flows
+        # {
+        #     "x": {"a": 2.0, "b": 1.0},
+        #     "a": {"c": 2.0},
+        #     "b": {"c": 0, "d": 1.0},
+        #     "c": {"y": 2.0},
+        #     "d": {"e": 1.0},
+        #     "e": {"y": 1.0},
+        #     "y": {},
+        # }
+        solnValue = 3.0
+        s = "x"
+        t = "y"
+
+        compare_flows_and_cuts(G, s, t, solnValue, capacity="spam")
+
+    def test_digraph_infcap_edges(self):
+        # DiGraph with infinite capacity edges
+        G = nx.DiGraph()
+        G.add_edge("s", "a")
+        G.add_edge("s", "b", capacity=30)
+        G.add_edge("a", "c", capacity=25)
+        G.add_edge("b", "c", capacity=12)
+        G.add_edge("a", "t", capacity=60)
+        G.add_edge("c", "t")
+
+        # H
+        # {
+        #     "s": {"a": 85, "b": 12},
+        #     "a": {"c": 25, "t": 60},
+        #     "b": {"c": 12},
+        #     "c": {"t": 37},
+        #     "t": {},
+        # }
+
+        compare_flows_and_cuts(G, "s", "t", 97)
+
+        # DiGraph with infinite capacity digon
+        G = nx.DiGraph()
+        G.add_edge("s", "a", capacity=85)
+        G.add_edge("s", "b", capacity=30)
+        G.add_edge("a", "c")
+        G.add_edge("c", "a")
+        G.add_edge("b", "c", capacity=12)
+        G.add_edge("a", "t", capacity=60)
+        G.add_edge("c", "t", capacity=37)
+
+        # H
+        # {
+        #     "s": {"a": 85, "b": 12},
+        #     "a": {"c": 25, "t": 60},
+        #     "c": {"a": 0, "t": 37},
+        #     "b": {"c": 12},
+        #     "t": {},
+        # }
+
+        compare_flows_and_cuts(G, "s", "t", 97)
+
+    def test_digraph_infcap_path(self):
+        # Graph with infinite capacity (s, t)-path
+        G = nx.DiGraph()
+        G.add_edge("s", "a")
+        G.add_edge("s", "b", capacity=30)
+        G.add_edge("a", "c")
+        G.add_edge("b", "c", capacity=12)
+        G.add_edge("a", "t", capacity=60)
+        G.add_edge("c", "t")
+
+        for flow_func in all_funcs:
+            pytest.raises(nx.NetworkXUnbounded, flow_func, G, "s", "t")
+
+    def test_graph_infcap_edges(self):
+        # Undirected graph with infinite capacity edges
+        G = nx.Graph()
+        G.add_edge("s", "a")
+        G.add_edge("s", "b", capacity=30)
+        G.add_edge("a", "c", capacity=25)
+        G.add_edge("b", "c", capacity=12)
+        G.add_edge("a", "t", capacity=60)
+        G.add_edge("c", "t")
+
+        # H
+        # {
+        #     "s": {"a": 85, "b": 12},
+        #     "a": {"c": 25, "s": 85, "t": 60},
+        #     "b": {"c": 12, "s": 12},
+        #     "c": {"a": 25, "b": 12, "t": 37},
+        #     "t": {"a": 60, "c": 37},
+        # }
+
+        compare_flows_and_cuts(G, "s", "t", 97)
+
+    def test_digraph5(self):
+        # From ticket #429 by mfrasca.
+        G = nx.DiGraph()
+        G.add_edge("s", "a", capacity=2)
+        G.add_edge("s", "b", capacity=2)
+        G.add_edge("a", "b", capacity=5)
+        G.add_edge("a", "t", capacity=1)
+        G.add_edge("b", "a", capacity=1)
+        G.add_edge("b", "t", capacity=3)
+        # flow solution
+        # {
+        #     "a": {"b": 1, "t": 1},
+        #     "b": {"a": 0, "t": 3},
+        #     "s": {"a": 2, "b": 2},
+        #     "t": {},
+        # }
+        compare_flows_and_cuts(G, "s", "t", 4)
+
+    def test_disconnected(self):
+        G = nx.Graph()
+        G.add_weighted_edges_from([(0, 1, 1), (1, 2, 1), (2, 3, 1)], weight="capacity")
+        G.remove_node(1)
+        assert nx.maximum_flow_value(G, 0, 3) == 0
+        # flow solution
+        # {0: {}, 2: {3: 0}, 3: {2: 0}}
+        compare_flows_and_cuts(G, 0, 3, 0)
+
+    def test_source_target_not_in_graph(self):
+        G = nx.Graph()
+        G.add_weighted_edges_from([(0, 1, 1), (1, 2, 1), (2, 3, 1)], weight="capacity")
+        G.remove_node(0)
+        for flow_func in all_funcs:
+            pytest.raises(nx.NetworkXError, flow_func, G, 0, 3)
+        G.add_weighted_edges_from([(0, 1, 1), (1, 2, 1), (2, 3, 1)], weight="capacity")
+        G.remove_node(3)
+        for flow_func in all_funcs:
+            pytest.raises(nx.NetworkXError, flow_func, G, 0, 3)
+
+    def test_source_target_coincide(self):
+        G = nx.Graph()
+        G.add_node(0)
+        for flow_func in all_funcs:
+            pytest.raises(nx.NetworkXError, flow_func, G, 0, 0)
+
+    def test_multigraphs_raise(self):
+        G = nx.MultiGraph()
+        M = nx.MultiDiGraph()
+        G.add_edges_from([(0, 1), (1, 0)], capacity=True)
+        for flow_func in all_funcs:
+            pytest.raises(nx.NetworkXError, flow_func, G, 0, 0)
+
+
+class TestMaxFlowMinCutInterface:
+    def setup_method(self):
+        G = nx.DiGraph()
+        G.add_edge("x", "a", capacity=3.0)
+        G.add_edge("x", "b", capacity=1.0)
+        G.add_edge("a", "c", capacity=3.0)
+        G.add_edge("b", "c", capacity=5.0)
+        G.add_edge("b", "d", capacity=4.0)
+        G.add_edge("d", "e", capacity=2.0)
+        G.add_edge("c", "y", capacity=2.0)
+        G.add_edge("e", "y", capacity=3.0)
+        self.G = G
+        H = nx.DiGraph()
+        H.add_edge(0, 1, capacity=1.0)
+        H.add_edge(1, 2, capacity=1.0)
+        self.H = H
+
+    def test_flow_func_not_callable(self):
+        elements = ["this_should_be_callable", 10, {1, 2, 3}]
+        G = nx.Graph()
+        G.add_weighted_edges_from([(0, 1, 1), (1, 2, 1), (2, 3, 1)], weight="capacity")
+        for flow_func in interface_funcs:
+            for element in elements:
+                pytest.raises(nx.NetworkXError, flow_func, G, 0, 1, flow_func=element)
+                pytest.raises(nx.NetworkXError, flow_func, G, 0, 1, flow_func=element)
+
+    def test_flow_func_parameters(self):
+        G = self.G
+        fv = 3.0
+        for interface_func in interface_funcs:
+            for flow_func in flow_funcs:
+                errmsg = (
+                    f"Assertion failed in function: {flow_func.__name__} "
+                    f"in interface {interface_func.__name__}"
+                )
+                result = interface_func(G, "x", "y", flow_func=flow_func)
+                if interface_func in max_min_funcs:
+                    result = result[0]
+                assert fv == result, errmsg
+
+    def test_minimum_cut_no_cutoff(self):
+        G = self.G
+        pytest.raises(
+            nx.NetworkXError,
+            nx.minimum_cut,
+            G,
+            "x",
+            "y",
+            flow_func=preflow_push,
+            cutoff=1.0,
+        )
+        pytest.raises(
+            nx.NetworkXError,
+            nx.minimum_cut_value,
+            G,
+            "x",
+            "y",
+            flow_func=preflow_push,
+            cutoff=1.0,
+        )
+
+    def test_kwargs(self):
+        G = self.H
+        fv = 1.0
+        to_test = (
+            (shortest_augmenting_path, {"two_phase": True}),
+            (preflow_push, {"global_relabel_freq": 5}),
+        )
+        for interface_func in interface_funcs:
+            for flow_func, kwargs in to_test:
+                errmsg = (
+                    f"Assertion failed in function: {flow_func.__name__} "
+                    f"in interface {interface_func.__name__}"
+                )
+                result = interface_func(G, 0, 2, flow_func=flow_func, **kwargs)
+                if interface_func in max_min_funcs:
+                    result = result[0]
+                assert fv == result, errmsg
+
+    def test_kwargs_default_flow_func(self):
+        G = self.H
+        for interface_func in interface_funcs:
+            pytest.raises(
+                nx.NetworkXError, interface_func, G, 0, 1, global_relabel_freq=2
+            )
+
+    def test_reusing_residual(self):
+        G = self.G
+        fv = 3.0
+        s, t = "x", "y"
+        R = build_residual_network(G, "capacity")
+        for interface_func in interface_funcs:
+            for flow_func in flow_funcs:
+                errmsg = (
+                    f"Assertion failed in function: {flow_func.__name__} "
+                    f"in interface {interface_func.__name__}"
+                )
+                for i in range(3):
+                    result = interface_func(
+                        G, "x", "y", flow_func=flow_func, residual=R
+                    )
+                    if interface_func in max_min_funcs:
+                        result = result[0]
+                    assert fv == result, errmsg
+
+
+# Tests specific to one algorithm
+def test_preflow_push_global_relabel_freq():
+    G = nx.DiGraph()
+    G.add_edge(1, 2, capacity=1)
+    R = preflow_push(G, 1, 2, global_relabel_freq=None)
+    assert R.graph["flow_value"] == 1
+    pytest.raises(nx.NetworkXError, preflow_push, G, 1, 2, global_relabel_freq=-1)
+
+
+def test_preflow_push_makes_enough_space():
+    # From ticket #1542
+    G = nx.DiGraph()
+    nx.add_path(G, [0, 1, 3], capacity=1)
+    nx.add_path(G, [1, 2, 3], capacity=1)
+    R = preflow_push(G, 0, 3, value_only=False)
+    assert R.graph["flow_value"] == 1
+
+
+def test_shortest_augmenting_path_two_phase():
+    k = 5
+    p = 1000
+    G = nx.DiGraph()
+    for i in range(k):
+        G.add_edge("s", (i, 0), capacity=1)
+        nx.add_path(G, ((i, j) for j in range(p)), capacity=1)
+        G.add_edge((i, p - 1), "t", capacity=1)
+    R = shortest_augmenting_path(G, "s", "t", two_phase=True)
+    assert R.graph["flow_value"] == k
+    R = shortest_augmenting_path(G, "s", "t", two_phase=False)
+    assert R.graph["flow_value"] == k
+
+
+class TestCutoff:
+    def test_cutoff(self):
+        k = 5
+        p = 1000
+        G = nx.DiGraph()
+        for i in range(k):
+            G.add_edge("s", (i, 0), capacity=2)
+            nx.add_path(G, ((i, j) for j in range(p)), capacity=2)
+            G.add_edge((i, p - 1), "t", capacity=2)
+        R = shortest_augmenting_path(G, "s", "t", two_phase=True, cutoff=k)
+        assert k <= R.graph["flow_value"] <= (2 * k)
+        R = shortest_augmenting_path(G, "s", "t", two_phase=False, cutoff=k)
+        assert k <= R.graph["flow_value"] <= (2 * k)
+        R = edmonds_karp(G, "s", "t", cutoff=k)
+        assert k <= R.graph["flow_value"] <= (2 * k)
+        R = dinitz(G, "s", "t", cutoff=k)
+        assert k <= R.graph["flow_value"] <= (2 * k)
+        R = boykov_kolmogorov(G, "s", "t", cutoff=k)
+        assert k <= R.graph["flow_value"] <= (2 * k)
+
+    def test_complete_graph_cutoff(self):
+        G = nx.complete_graph(5)
+        nx.set_edge_attributes(G, {(u, v): 1 for u, v in G.edges()}, "capacity")
+        for flow_func in [
+            shortest_augmenting_path,
+            edmonds_karp,
+            dinitz,
+            boykov_kolmogorov,
+        ]:
+            for cutoff in [3, 2, 1]:
+                result = nx.maximum_flow_value(
+                    G, 0, 4, flow_func=flow_func, cutoff=cutoff
+                )
+                assert cutoff == result, f"cutoff error in {flow_func.__name__}"

janus/lib/python3.10/site-packages/networkx/algorithms/flow/tests/test_networksimplex.py

@@ -0,0 +1,387 @@
+import bz2
+import importlib.resources
+import os
+import pickle
+
+import pytest
+
+import networkx as nx
+
+
+@pytest.fixture
+def simple_flow_graph():
+    G = nx.DiGraph()
+    G.add_node("a", demand=0)
+    G.add_node("b", demand=-5)
+    G.add_node("c", demand=50000000)
+    G.add_node("d", demand=-49999995)
+    G.add_edge("a", "b", weight=3, capacity=4)
+    G.add_edge("a", "c", weight=6, capacity=10)
+    G.add_edge("b", "d", weight=1, capacity=9)
+    G.add_edge("c", "d", weight=2, capacity=5)
+    return G
+
+
+@pytest.fixture
+def simple_no_flow_graph():
+    G = nx.DiGraph()
+    G.add_node("s", demand=-5)
+    G.add_node("t", demand=5)
+    G.add_edge("s", "a", weight=1, capacity=3)
+    G.add_edge("a", "b", weight=3)
+    G.add_edge("a", "c", weight=-6)
+    G.add_edge("b", "d", weight=1)
+    G.add_edge("c", "d", weight=-2)
+    G.add_edge("d", "t", weight=1, capacity=3)
+    return G
+
+
+def get_flowcost_from_flowdict(G, flowDict):
+    """Returns flow cost calculated from flow dictionary"""
+    flowCost = 0
+    for u in flowDict:
+        for v in flowDict[u]:
+            flowCost += flowDict[u][v] * G[u][v]["weight"]
+    return flowCost
+
+
+def test_infinite_demand_raise(simple_flow_graph):
+    G = simple_flow_graph
+    inf = float("inf")
+    nx.set_node_attributes(G, {"a": {"demand": inf}})
+    pytest.raises(nx.NetworkXError, nx.network_simplex, G)
+
+
+def test_neg_infinite_demand_raise(simple_flow_graph):
+    G = simple_flow_graph
+    inf = float("inf")
+    nx.set_node_attributes(G, {"a": {"demand": -inf}})
+    pytest.raises(nx.NetworkXError, nx.network_simplex, G)
+
+
+def test_infinite_weight_raise(simple_flow_graph):
+    G = simple_flow_graph
+    inf = float("inf")
+    nx.set_edge_attributes(
+        G, {("a", "b"): {"weight": inf}, ("b", "d"): {"weight": inf}}
+    )
+    pytest.raises(nx.NetworkXError, nx.network_simplex, G)
+
+
+def test_nonzero_net_demand_raise(simple_flow_graph):
+    G = simple_flow_graph
+    nx.set_node_attributes(G, {"b": {"demand": -4}})
+    pytest.raises(nx.NetworkXUnfeasible, nx.network_simplex, G)
+
+
+def test_negative_capacity_raise(simple_flow_graph):
+    G = simple_flow_graph
+    nx.set_edge_attributes(G, {("a", "b"): {"weight": 1}, ("b", "d"): {"capacity": -9}})
+    pytest.raises(nx.NetworkXUnfeasible, nx.network_simplex, G)
+
+
+def test_no_flow_satisfying_demands(simple_no_flow_graph):
+    G = simple_no_flow_graph
+    pytest.raises(nx.NetworkXUnfeasible, nx.network_simplex, G)
+
+
+def test_sum_demands_not_zero(simple_no_flow_graph):
+    G = simple_no_flow_graph
+    nx.set_node_attributes(G, {"t": {"demand": 4}})
+    pytest.raises(nx.NetworkXUnfeasible, nx.network_simplex, G)
+
+
+def test_google_or_tools_example():
+    """
+    https://developers.google.com/optimization/flow/mincostflow
+    """
+    G = nx.DiGraph()
+    start_nodes = [0, 0, 1, 1, 1, 2, 2, 3, 4]
+    end_nodes = [1, 2, 2, 3, 4, 3, 4, 4, 2]
+    capacities = [15, 8, 20, 4, 10, 15, 4, 20, 5]
+    unit_costs = [4, 4, 2, 2, 6, 1, 3, 2, 3]
+    supplies = [20, 0, 0, -5, -15]
+    answer = 150
+
+    for i in range(len(supplies)):
+        G.add_node(i, demand=(-1) * supplies[i])  # supplies are negative of demand
+
+    for i in range(len(start_nodes)):
+        G.add_edge(
+            start_nodes[i], end_nodes[i], weight=unit_costs[i], capacity=capacities[i]
+        )
+
+    flowCost, flowDict = nx.network_simplex(G)
+    assert flowCost == answer
+    assert flowCost == get_flowcost_from_flowdict(G, flowDict)
+
+
+def test_google_or_tools_example2():
+    """
+    https://developers.google.com/optimization/flow/mincostflow
+    """
+    G = nx.DiGraph()
+    start_nodes = [0, 0, 1, 1, 1, 2, 2, 3, 4, 3]
+    end_nodes = [1, 2, 2, 3, 4, 3, 4, 4, 2, 5]
+    capacities = [15, 8, 20, 4, 10, 15, 4, 20, 5, 10]
+    unit_costs = [4, 4, 2, 2, 6, 1, 3, 2, 3, 4]
+    supplies = [23, 0, 0, -5, -15, -3]
+    answer = 183
+
+    for i in range(len(supplies)):
+        G.add_node(i, demand=(-1) * supplies[i])  # supplies are negative of demand
+
+    for i in range(len(start_nodes)):
+        G.add_edge(
+            start_nodes[i], end_nodes[i], weight=unit_costs[i], capacity=capacities[i]
+        )
+
+    flowCost, flowDict = nx.network_simplex(G)
+    assert flowCost == answer
+    assert flowCost == get_flowcost_from_flowdict(G, flowDict)
+
+
+def test_large():
+    fname = (
+        importlib.resources.files("networkx.algorithms.flow.tests")
+        / "netgen-2.gpickle.bz2"
+    )
+
+    with bz2.BZ2File(fname, "rb") as f:
+        G = pickle.load(f)
+    flowCost, flowDict = nx.network_simplex(G)
+    assert 6749969302 == flowCost
+    assert 6749969302 == nx.cost_of_flow(G, flowDict)
+
+
+def test_simple_digraph():
+    G = nx.DiGraph()
+    G.add_node("a", demand=-5)
+    G.add_node("d", demand=5)
+    G.add_edge("a", "b", weight=3, capacity=4)
+    G.add_edge("a", "c", weight=6, capacity=10)
+    G.add_edge("b", "d", weight=1, capacity=9)
+    G.add_edge("c", "d", weight=2, capacity=5)
+    flowCost, H = nx.network_simplex(G)
+    soln = {"a": {"b": 4, "c": 1}, "b": {"d": 4}, "c": {"d": 1}, "d": {}}
+    assert flowCost == 24
+    assert nx.min_cost_flow_cost(G) == 24
+    assert H == soln
+
+
+def test_negcycle_infcap():
+    G = nx.DiGraph()
+    G.add_node("s", demand=-5)
+    G.add_node("t", demand=5)
+    G.add_edge("s", "a", weight=1, capacity=3)
+    G.add_edge("a", "b", weight=3)
+    G.add_edge("c", "a", weight=-6)
+    G.add_edge("b", "d", weight=1)
+    G.add_edge("d", "c", weight=-2)
+    G.add_edge("d", "t", weight=1, capacity=3)
+    pytest.raises(nx.NetworkXUnfeasible, nx.network_simplex, G)
+
+
+def test_transshipment():
+    G = nx.DiGraph()
+    G.add_node("a", demand=1)
+    G.add_node("b", demand=-2)
+    G.add_node("c", demand=-2)
+    G.add_node("d", demand=3)
+    G.add_node("e", demand=-4)
+    G.add_node("f", demand=-4)
+    G.add_node("g", demand=3)
+    G.add_node("h", demand=2)
+    G.add_node("r", demand=3)
+    G.add_edge("a", "c", weight=3)
+    G.add_edge("r", "a", weight=2)
+    G.add_edge("b", "a", weight=9)
+    G.add_edge("r", "c", weight=0)
+    G.add_edge("b", "r", weight=-6)
+    G.add_edge("c", "d", weight=5)
+    G.add_edge("e", "r", weight=4)
+    G.add_edge("e", "f", weight=3)
+    G.add_edge("h", "b", weight=4)
+    G.add_edge("f", "d", weight=7)
+    G.add_edge("f", "h", weight=12)
+    G.add_edge("g", "d", weight=12)
+    G.add_edge("f", "g", weight=-1)
+    G.add_edge("h", "g", weight=-10)
+    flowCost, H = nx.network_simplex(G)
+    soln = {
+        "a": {"c": 0},
+        "b": {"a": 0, "r": 2},
+        "c": {"d": 3},
+        "d": {},
+        "e": {"r": 3, "f": 1},
+        "f": {"d": 0, "g": 3, "h": 2},
+        "g": {"d": 0},
+        "h": {"b": 0, "g": 0},
+        "r": {"a": 1, "c": 1},
+    }
+    assert flowCost == 41
+    assert H == soln
+
+
+def test_digraph1():
+    # From Bradley, S. P., Hax, A. C. and Magnanti, T. L. Applied
+    # Mathematical Programming. Addison-Wesley, 1977.
+    G = nx.DiGraph()
+    G.add_node(1, demand=-20)
+    G.add_node(4, demand=5)
+    G.add_node(5, demand=15)
+    G.add_edges_from(
+        [
+            (1, 2, {"capacity": 15, "weight": 4}),
+            (1, 3, {"capacity": 8, "weight": 4}),
+            (2, 3, {"weight": 2}),
+            (2, 4, {"capacity": 4, "weight": 2}),
+            (2, 5, {"capacity": 10, "weight": 6}),
+            (3, 4, {"capacity": 15, "weight": 1}),
+            (3, 5, {"capacity": 5, "weight": 3}),
+            (4, 5, {"weight": 2}),
+            (5, 3, {"capacity": 4, "weight": 1}),
+        ]
+    )
+    flowCost, H = nx.network_simplex(G)
+    soln = {
+        1: {2: 12, 3: 8},
+        2: {3: 8, 4: 4, 5: 0},
+        3: {4: 11, 5: 5},
+        4: {5: 10},
+        5: {3: 0},
+    }
+    assert flowCost == 150
+    assert nx.min_cost_flow_cost(G) == 150
+    assert H == soln
+
+
+def test_zero_capacity_edges():
+    """Address issue raised in ticket #617 by arv."""
+    G = nx.DiGraph()
+    G.add_edges_from(
+        [
+            (1, 2, {"capacity": 1, "weight": 1}),
+            (1, 5, {"capacity": 1, "weight": 1}),
+            (2, 3, {"capacity": 0, "weight": 1}),
+            (2, 5, {"capacity": 1, "weight": 1}),
+            (5, 3, {"capacity": 2, "weight": 1}),
+            (5, 4, {"capacity": 0, "weight": 1}),
+            (3, 4, {"capacity": 2, "weight": 1}),
+        ]
+    )
+    G.nodes[1]["demand"] = -1
+    G.nodes[2]["demand"] = -1
+    G.nodes[4]["demand"] = 2
+
+    flowCost, H = nx.network_simplex(G)
+    soln = {1: {2: 0, 5: 1}, 2: {3: 0, 5: 1}, 3: {4: 2}, 4: {}, 5: {3: 2, 4: 0}}
+    assert flowCost == 6
+    assert nx.min_cost_flow_cost(G) == 6
+    assert H == soln
+
+
+def test_digon():
+    """Check if digons are handled properly. Taken from ticket
+    #618 by arv."""
+    nodes = [(1, {}), (2, {"demand": -4}), (3, {"demand": 4})]
+    edges = [
+        (1, 2, {"capacity": 3, "weight": 600000}),
+        (2, 1, {"capacity": 2, "weight": 0}),
+        (2, 3, {"capacity": 5, "weight": 714285}),
+        (3, 2, {"capacity": 2, "weight": 0}),
+    ]
+    G = nx.DiGraph(edges)
+    G.add_nodes_from(nodes)
+    flowCost, H = nx.network_simplex(G)
+    soln = {1: {2: 0}, 2: {1: 0, 3: 4}, 3: {2: 0}}
+    assert flowCost == 2857140
+
+
+def test_deadend():
+    """Check if one-node cycles are handled properly. Taken from ticket
+    #2906 from @sshraven."""
+    G = nx.DiGraph()
+
+    G.add_nodes_from(range(5), demand=0)
+    G.nodes[4]["demand"] = -13
+    G.nodes[3]["demand"] = 13
+
+    G.add_edges_from([(0, 2), (0, 3), (2, 1)], capacity=20, weight=0.1)
+    pytest.raises(nx.NetworkXUnfeasible, nx.network_simplex, G)
+
+
+def test_infinite_capacity_neg_digon():
+    """An infinite capacity negative cost digon results in an unbounded
+    instance."""
+    nodes = [(1, {}), (2, {"demand": -4}), (3, {"demand": 4})]
+    edges = [
+        (1, 2, {"weight": -600}),
+        (2, 1, {"weight": 0}),
+        (2, 3, {"capacity": 5, "weight": 714285}),
+        (3, 2, {"capacity": 2, "weight": 0}),
+    ]
+    G = nx.DiGraph(edges)
+    G.add_nodes_from(nodes)
+    pytest.raises(nx.NetworkXUnbounded, nx.network_simplex, G)
+
+
+def test_multidigraph():
+    """Multidigraphs are acceptable."""
+    G = nx.MultiDiGraph()
+    G.add_weighted_edges_from([(1, 2, 1), (2, 3, 2)], weight="capacity")
+    flowCost, H = nx.network_simplex(G)
+    assert flowCost == 0
+    assert H == {1: {2: {0: 0}}, 2: {3: {0: 0}}, 3: {}}
+
+
+def test_negative_selfloops():
+    """Negative selfloops should cause an exception if uncapacitated and
+    always be saturated otherwise.
+    """
+    G = nx.DiGraph()
+    G.add_edge(1, 1, weight=-1)
+    pytest.raises(nx.NetworkXUnbounded, nx.network_simplex, G)
+
+    G[1][1]["capacity"] = 2
+    flowCost, H = nx.network_simplex(G)
+    assert flowCost == -2
+    assert H == {1: {1: 2}}
+
+    G = nx.MultiDiGraph()
+    G.add_edge(1, 1, "x", weight=-1)
+    G.add_edge(1, 1, "y", weight=1)
+    pytest.raises(nx.NetworkXUnbounded, nx.network_simplex, G)
+
+    G[1][1]["x"]["capacity"] = 2
+    flowCost, H = nx.network_simplex(G)
+    assert flowCost == -2
+    assert H == {1: {1: {"x": 2, "y": 0}}}
+
+
+def test_bone_shaped():
+    # From #1283
+    G = nx.DiGraph()
+    G.add_node(0, demand=-4)
+    G.add_node(1, demand=2)
+    G.add_node(2, demand=2)
+    G.add_node(3, demand=4)
+    G.add_node(4, demand=-2)
+    G.add_node(5, demand=-2)
+    G.add_edge(0, 1, capacity=4)
+    G.add_edge(0, 2, capacity=4)
+    G.add_edge(4, 3, capacity=4)
+    G.add_edge(5, 3, capacity=4)
+    G.add_edge(0, 3, capacity=0)
+    flowCost, H = nx.network_simplex(G)
+    assert flowCost == 0
+    assert H == {0: {1: 2, 2: 2, 3: 0}, 1: {}, 2: {}, 3: {}, 4: {3: 2}, 5: {3: 2}}
+
+
+def test_graphs_type_exceptions():
+    G = nx.Graph()
+    pytest.raises(nx.NetworkXNotImplemented, nx.network_simplex, G)
+    G = nx.MultiGraph()
+    pytest.raises(nx.NetworkXNotImplemented, nx.network_simplex, G)
+    G = nx.DiGraph()
+    pytest.raises(nx.NetworkXError, nx.network_simplex, G)

janus/lib/python3.10/site-packages/networkx/algorithms/flow/utils.py

@@ -0,0 +1,189 @@
+"""
+Utility classes and functions for network flow algorithms.
+"""
+
+from collections import deque
+
+import networkx as nx
+
+__all__ = [
+    "CurrentEdge",
+    "Level",
+    "GlobalRelabelThreshold",
+    "build_residual_network",
+    "detect_unboundedness",
+    "build_flow_dict",
+]
+
+
+class CurrentEdge:
+    """Mechanism for iterating over out-edges incident to a node in a circular
+    manner. StopIteration exception is raised when wraparound occurs.
+    """
+
+    __slots__ = ("_edges", "_it", "_curr")
+
+    def __init__(self, edges):
+        self._edges = edges
+        if self._edges:
+            self._rewind()
+
+    def get(self):
+        return self._curr
+
+    def move_to_next(self):
+        try:
+            self._curr = next(self._it)
+        except StopIteration:
+            self._rewind()
+            raise
+
+    def _rewind(self):
+        self._it = iter(self._edges.items())
+        self._curr = next(self._it)
+
+
+class Level:
+    """Active and inactive nodes in a level."""
+
+    __slots__ = ("active", "inactive")
+
+    def __init__(self):
+        self.active = set()
+        self.inactive = set()
+
+
+class GlobalRelabelThreshold:
+    """Measurement of work before the global relabeling heuristic should be
+    applied.
+    """
+
+    def __init__(self, n, m, freq):
+        self._threshold = (n + m) / freq if freq else float("inf")
+        self._work = 0
+
+    def add_work(self, work):
+        self._work += work
+
+    def is_reached(self):
+        return self._work >= self._threshold
+
+    def clear_work(self):
+        self._work = 0
+
+
+@nx._dispatchable(edge_attrs={"capacity": float("inf")}, returns_graph=True)
+def build_residual_network(G, capacity):
+    """Build a residual network and initialize a zero flow.
+
+    The residual network :samp:`R` from an input graph :samp:`G` has the
+    same nodes as :samp:`G`. :samp:`R` is a DiGraph that contains a pair
+    of edges :samp:`(u, v)` and :samp:`(v, u)` iff :samp:`(u, v)` is not a
+    self-loop, and at least one of :samp:`(u, v)` and :samp:`(v, u)` exists
+    in :samp:`G`.
+
+    For each edge :samp:`(u, v)` in :samp:`R`, :samp:`R[u][v]['capacity']`
+    is equal to the capacity of :samp:`(u, v)` in :samp:`G` if it exists
+    in :samp:`G` or zero otherwise. If the capacity is infinite,
+    :samp:`R[u][v]['capacity']` will have a high arbitrary finite value
+    that does not affect the solution of the problem. This value is stored in
+    :samp:`R.graph['inf']`. For each edge :samp:`(u, v)` in :samp:`R`,
+    :samp:`R[u][v]['flow']` represents the flow function of :samp:`(u, v)` and
+    satisfies :samp:`R[u][v]['flow'] == -R[v][u]['flow']`.
+
+    The flow value, defined as the total flow into :samp:`t`, the sink, is
+    stored in :samp:`R.graph['flow_value']`. If :samp:`cutoff` is not
+    specified, reachability to :samp:`t` using only edges :samp:`(u, v)` such
+    that :samp:`R[u][v]['flow'] < R[u][v]['capacity']` induces a minimum
+    :samp:`s`-:samp:`t` cut.
+
+    """
+    if G.is_multigraph():
+        raise nx.NetworkXError("MultiGraph and MultiDiGraph not supported (yet).")
+
+    R = nx.DiGraph()
+    R.__networkx_cache__ = None  # Disable caching
+    R.add_nodes_from(G)
+
+    inf = float("inf")
+    # Extract edges with positive capacities. Self loops excluded.
+    edge_list = [
+        (u, v, attr)
+        for u, v, attr in G.edges(data=True)
+        if u != v and attr.get(capacity, inf) > 0
+    ]
+    # Simulate infinity with three times the sum of the finite edge capacities
+    # or any positive value if the sum is zero. This allows the
+    # infinite-capacity edges to be distinguished for unboundedness detection
+    # and directly participate in residual capacity calculation. If the maximum
+    # flow is finite, these edges cannot appear in the minimum cut and thus
+    # guarantee correctness. Since the residual capacity of an
+    # infinite-capacity edge is always at least 2/3 of inf, while that of an
+    # finite-capacity edge is at most 1/3 of inf, if an operation moves more
+    # than 1/3 of inf units of flow to t, there must be an infinite-capacity
+    # s-t path in G.
+    inf = (
+        3
+        * sum(
+            attr[capacity]
+            for u, v, attr in edge_list
+            if capacity in attr and attr[capacity] != inf
+        )
+        or 1
+    )
+    if G.is_directed():
+        for u, v, attr in edge_list:
+            r = min(attr.get(capacity, inf), inf)
+            if not R.has_edge(u, v):
+                # Both (u, v) and (v, u) must be present in the residual
+                # network.
+                R.add_edge(u, v, capacity=r)
+                R.add_edge(v, u, capacity=0)
+            else:
+                # The edge (u, v) was added when (v, u) was visited.
+                R[u][v]["capacity"] = r
+    else:
+        for u, v, attr in edge_list:
+            # Add a pair of edges with equal residual capacities.
+            r = min(attr.get(capacity, inf), inf)
+            R.add_edge(u, v, capacity=r)
+            R.add_edge(v, u, capacity=r)
+
+    # Record the value simulating infinity.
+    R.graph["inf"] = inf
+
+    return R
+
+
+@nx._dispatchable(
+    graphs="R",
+    preserve_edge_attrs={"R": {"capacity": float("inf")}},
+    preserve_graph_attrs=True,
+)
+def detect_unboundedness(R, s, t):
+    """Detect an infinite-capacity s-t path in R."""
+    q = deque([s])
+    seen = {s}
+    inf = R.graph["inf"]
+    while q:
+        u = q.popleft()
+        for v, attr in R[u].items():
+            if attr["capacity"] == inf and v not in seen:
+                if v == t:
+                    raise nx.NetworkXUnbounded(
+                        "Infinite capacity path, flow unbounded above."
+                    )
+                seen.add(v)
+                q.append(v)
+
+
+@nx._dispatchable(graphs={"G": 0, "R": 1}, preserve_edge_attrs={"R": {"flow": None}})
+def build_flow_dict(G, R):
+    """Build a flow dictionary from a residual network."""
+    flow_dict = {}
+    for u in G:
+        flow_dict[u] = {v: 0 for v in G[u]}
+        flow_dict[u].update(
+            (v, attr["flow"]) for v, attr in R[u].items() if attr["flow"] > 0
+        )
+    return flow_dict

janus/lib/python3.10/site-packages/networkx/algorithms/traversal/beamsearch.py

@@ -0,0 +1,90 @@
+"""Basic algorithms for breadth-first searching the nodes of a graph."""
+
+import networkx as nx
+
+__all__ = ["bfs_beam_edges"]
+
+
+@nx._dispatchable
+def bfs_beam_edges(G, source, value, width=None):
+    """Iterates over edges in a beam search.
+
+    The beam search is a generalized breadth-first search in which only
+    the "best" *w* neighbors of the current node are enqueued, where *w*
+    is the beam width and "best" is an application-specific
+    heuristic. In general, a beam search with a small beam width might
+    not visit each node in the graph.
+
+    .. note::
+
+       With the default value of ``width=None`` or `width` greater than the
+       maximum degree of the graph, this function equates to a slower
+       version of `~networkx.algorithms.traversal.breadth_first_search.bfs_edges`.
+       All nodes will be visited, though the order of the reported edges may
+       vary. In such cases, `value` has no effect - consider using `bfs_edges`
+       directly instead.
+
+    Parameters
+    ----------
+    G : NetworkX graph
+
+    source : node
+        Starting node for the breadth-first search; this function
+        iterates over only those edges in the component reachable from
+        this node.
+
+    value : function
+        A function that takes a node of the graph as input and returns a
+        real number indicating how "good" it is. A higher value means it
+        is more likely to be visited sooner during the search. When
+        visiting a new node, only the `width` neighbors with the highest
+        `value` are enqueued (in decreasing order of `value`).
+
+    width : int (default = None)
+        The beam width for the search. This is the number of neighbors
+        (ordered by `value`) to enqueue when visiting each new node.
+
+    Yields
+    ------
+    edge
+        Edges in the beam search starting from `source`, given as a pair
+        of nodes.
+
+    Examples
+    --------
+    To give nodes with, for example, a higher centrality precedence
+    during the search, set the `value` function to return the centrality
+    value of the node:
+
+    >>> G = nx.karate_club_graph()
+    >>> centrality = nx.eigenvector_centrality(G)
+    >>> list(nx.bfs_beam_edges(G, source=0, value=centrality.get, width=3))
+    [(0, 2), (0, 1), (0, 8), (2, 32), (1, 13), (8, 33)]
+    """
+
+    if width is None:
+        width = len(G)
+
+    def successors(v):
+        """Returns a list of the best neighbors of a node.
+
+        `v` is a node in the graph `G`.
+
+        The "best" neighbors are chosen according to the `value`
+        function (higher is better). Only the `width` best neighbors of
+        `v` are returned.
+        """
+        # TODO The Python documentation states that for small values, it
+        # is better to use `heapq.nlargest`. We should determine the
+        # threshold at which its better to use `heapq.nlargest()`
+        # instead of `sorted()[:]` and apply that optimization here.
+        #
+        # If `width` is greater than the number of neighbors of `v`, all
+        # neighbors are returned by the semantics of slicing in
+        # Python. This occurs in the special case that the user did not
+        # specify a `width`: in this case all neighbors are always
+        # returned, so this is just a (slower) implementation of
+        # `bfs_edges(G, source)` but with a sorted enqueue step.
+        return iter(sorted(G.neighbors(v), key=value, reverse=True)[:width])
+
+    yield from nx.generic_bfs_edges(G, source, successors)

janus/lib/python3.10/site-packages/networkx/algorithms/traversal/breadth_first_search.py

@@ -0,0 +1,575 @@
+"""Basic algorithms for breadth-first searching the nodes of a graph."""
+
+from collections import deque
+
+import networkx as nx
+
+__all__ = [
+    "bfs_edges",
+    "bfs_tree",
+    "bfs_predecessors",
+    "bfs_successors",
+    "descendants_at_distance",
+    "bfs_layers",
+    "bfs_labeled_edges",
+    "generic_bfs_edges",
+]
+
+
+@nx._dispatchable
+def generic_bfs_edges(G, source, neighbors=None, depth_limit=None):
+    """Iterate over edges in a breadth-first search.
+
+    The breadth-first search begins at `source` and enqueues the
+    neighbors of newly visited nodes specified by the `neighbors`
+    function.
+
+    Parameters
+    ----------
+    G : NetworkX graph
+
+    source : node
+        Starting node for the breadth-first search; this function
+        iterates over only those edges in the component reachable from
+        this node.
+
+    neighbors : function
+        A function that takes a newly visited node of the graph as input
+        and returns an *iterator* (not just a list) of nodes that are
+        neighbors of that node with custom ordering. If not specified, this is
+        just the ``G.neighbors`` method, but in general it can be any function
+        that returns an iterator over some or all of the neighbors of a
+        given node, in any order.
+
+    depth_limit : int, optional(default=len(G))
+        Specify the maximum search depth.
+
+    Yields
+    ------
+    edge
+        Edges in the breadth-first search starting from `source`.
+
+    Examples
+    --------
+    >>> G = nx.path_graph(7)
+    >>> list(nx.generic_bfs_edges(G, source=0))
+    [(0, 1), (1, 2), (2, 3), (3, 4), (4, 5), (5, 6)]
+    >>> list(nx.generic_bfs_edges(G, source=2))
+    [(2, 1), (2, 3), (1, 0), (3, 4), (4, 5), (5, 6)]
+    >>> list(nx.generic_bfs_edges(G, source=2, depth_limit=2))
+    [(2, 1), (2, 3), (1, 0), (3, 4)]
+
+    The `neighbors` param can be used to specify the visitation order of each
+    node's neighbors generically. In the following example, we modify the default
+    neighbor to return *odd* nodes first:
+
+    >>> def odd_first(n):
+    ...     return sorted(G.neighbors(n), key=lambda x: x % 2, reverse=True)
+
+    >>> G = nx.star_graph(5)
+    >>> list(nx.generic_bfs_edges(G, source=0))  # Default neighbor ordering
+    [(0, 1), (0, 2), (0, 3), (0, 4), (0, 5)]
+    >>> list(nx.generic_bfs_edges(G, source=0, neighbors=odd_first))
+    [(0, 1), (0, 3), (0, 5), (0, 2), (0, 4)]
+
+    Notes
+    -----
+    This implementation is from `PADS`_, which was in the public domain
+    when it was first accessed in July, 2004.  The modifications
+    to allow depth limits are based on the Wikipedia article
+    "`Depth-limited-search`_".
+
+    .. _PADS: http://www.ics.uci.edu/~eppstein/PADS/BFS.py
+    .. _Depth-limited-search: https://en.wikipedia.org/wiki/Depth-limited_search
+    """
+    if neighbors is None:
+        neighbors = G.neighbors
+    if depth_limit is None:
+        depth_limit = len(G)
+
+    seen = {source}
+    n = len(G)
+    depth = 0
+    next_parents_children = [(source, neighbors(source))]
+    while next_parents_children and depth < depth_limit:
+        this_parents_children = next_parents_children
+        next_parents_children = []
+        for parent, children in this_parents_children:
+            for child in children:
+                if child not in seen:
+                    seen.add(child)
+                    next_parents_children.append((child, neighbors(child)))
+                    yield parent, child
+            if len(seen) == n:
+                return
+        depth += 1
+
+
+@nx._dispatchable
+def bfs_edges(G, source, reverse=False, depth_limit=None, sort_neighbors=None):
+    """Iterate over edges in a breadth-first-search starting at source.
+
+    Parameters
+    ----------
+    G : NetworkX graph
+
+    source : node
+       Specify starting node for breadth-first search; this function
+       iterates over only those edges in the component reachable from
+       this node.
+
+    reverse : bool, optional
+       If True traverse a directed graph in the reverse direction
+
+    depth_limit : int, optional(default=len(G))
+        Specify the maximum search depth
+
+    sort_neighbors : function (default=None)
+        A function that takes an iterator over nodes as the input, and
+        returns an iterable of the same nodes with a custom ordering.
+        For example, `sorted` will sort the nodes in increasing order.
+
+    Yields
+    ------
+    edge: 2-tuple of nodes
+       Yields edges resulting from the breadth-first search.
+
+    Examples
+    --------
+    To get the edges in a breadth-first search::
+
+        >>> G = nx.path_graph(3)
+        >>> list(nx.bfs_edges(G, 0))
+        [(0, 1), (1, 2)]
+        >>> list(nx.bfs_edges(G, source=0, depth_limit=1))
+        [(0, 1)]
+
+    To get the nodes in a breadth-first search order::
+
+        >>> G = nx.path_graph(3)
+        >>> root = 2
+        >>> edges = nx.bfs_edges(G, root)
+        >>> nodes = [root] + [v for u, v in edges]
+        >>> nodes
+        [2, 1, 0]
+
+    Notes
+    -----
+    The naming of this function is very similar to
+    :func:`~networkx.algorithms.traversal.edgebfs.edge_bfs`. The difference
+    is that ``edge_bfs`` yields edges even if they extend back to an already
+    explored node while this generator yields the edges of the tree that results
+    from a breadth-first-search (BFS) so no edges are reported if they extend
+    to already explored nodes. That means ``edge_bfs`` reports all edges while
+    ``bfs_edges`` only reports those traversed by a node-based BFS. Yet another
+    description is that ``bfs_edges`` reports the edges traversed during BFS
+    while ``edge_bfs`` reports all edges in the order they are explored.
+
+    Based on the breadth-first search implementation in PADS [1]_
+    by D. Eppstein, July 2004; with modifications to allow depth limits
+    as described in [2]_.
+
+    References
+    ----------
+    .. [1] http://www.ics.uci.edu/~eppstein/PADS/BFS.py.
+    .. [2] https://en.wikipedia.org/wiki/Depth-limited_search
+
+    See Also
+    --------
+    bfs_tree
+    :func:`~networkx.algorithms.traversal.depth_first_search.dfs_edges`
+    :func:`~networkx.algorithms.traversal.edgebfs.edge_bfs`
+
+    """
+    if reverse and G.is_directed():
+        successors = G.predecessors
+    else:
+        successors = G.neighbors
+
+    if sort_neighbors is not None:
+        yield from generic_bfs_edges(
+            G, source, lambda node: iter(sort_neighbors(successors(node))), depth_limit
+        )
+    else:
+        yield from generic_bfs_edges(G, source, successors, depth_limit)
+
+
+@nx._dispatchable(returns_graph=True)
+def bfs_tree(G, source, reverse=False, depth_limit=None, sort_neighbors=None):
+    """Returns an oriented tree constructed from of a breadth-first-search
+    starting at source.
+
+    Parameters
+    ----------
+    G : NetworkX graph
+
+    source : node
+       Specify starting node for breadth-first search
+
+    reverse : bool, optional
+       If True traverse a directed graph in the reverse direction
+
+    depth_limit : int, optional(default=len(G))
+        Specify the maximum search depth
+
+    sort_neighbors : function (default=None)
+        A function that takes an iterator over nodes as the input, and
+        returns an iterable of the same nodes with a custom ordering.
+        For example, `sorted` will sort the nodes in increasing order.
+
+    Returns
+    -------
+    T: NetworkX DiGraph
+       An oriented tree
+
+    Examples
+    --------
+    >>> G = nx.path_graph(3)
+    >>> list(nx.bfs_tree(G, 1).edges())
+    [(1, 0), (1, 2)]
+    >>> H = nx.Graph()
+    >>> nx.add_path(H, [0, 1, 2, 3, 4, 5, 6])
+    >>> nx.add_path(H, [2, 7, 8, 9, 10])
+    >>> sorted(list(nx.bfs_tree(H, source=3, depth_limit=3).edges()))
+    [(1, 0), (2, 1), (2, 7), (3, 2), (3, 4), (4, 5), (5, 6), (7, 8)]
+
+
+    Notes
+    -----
+    Based on http://www.ics.uci.edu/~eppstein/PADS/BFS.py
+    by D. Eppstein, July 2004. The modifications
+    to allow depth limits based on the Wikipedia article
+    "`Depth-limited-search`_".
+
+    .. _Depth-limited-search: https://en.wikipedia.org/wiki/Depth-limited_search
+
+    See Also
+    --------
+    dfs_tree
+    bfs_edges
+    edge_bfs
+    """
+    T = nx.DiGraph()
+    T.add_node(source)
+    edges_gen = bfs_edges(
+        G,
+        source,
+        reverse=reverse,
+        depth_limit=depth_limit,
+        sort_neighbors=sort_neighbors,
+    )
+    T.add_edges_from(edges_gen)
+    return T
+
+
+@nx._dispatchable
+def bfs_predecessors(G, source, depth_limit=None, sort_neighbors=None):
+    """Returns an iterator of predecessors in breadth-first-search from source.
+
+    Parameters
+    ----------
+    G : NetworkX graph
+
+    source : node
+       Specify starting node for breadth-first search
+
+    depth_limit : int, optional(default=len(G))
+        Specify the maximum search depth
+
+    sort_neighbors : function (default=None)
+        A function that takes an iterator over nodes as the input, and
+        returns an iterable of the same nodes with a custom ordering.
+        For example, `sorted` will sort the nodes in increasing order.
+
+    Returns
+    -------
+    pred: iterator
+        (node, predecessor) iterator where `predecessor` is the predecessor of
+        `node` in a breadth first search starting from `source`.
+
+    Examples
+    --------
+    >>> G = nx.path_graph(3)
+    >>> dict(nx.bfs_predecessors(G, 0))
+    {1: 0, 2: 1}
+    >>> H = nx.Graph()
+    >>> H.add_edges_from([(0, 1), (0, 2), (1, 3), (1, 4), (2, 5), (2, 6)])
+    >>> dict(nx.bfs_predecessors(H, 0))
+    {1: 0, 2: 0, 3: 1, 4: 1, 5: 2, 6: 2}
+    >>> M = nx.Graph()
+    >>> nx.add_path(M, [0, 1, 2, 3, 4, 5, 6])
+    >>> nx.add_path(M, [2, 7, 8, 9, 10])
+    >>> sorted(nx.bfs_predecessors(M, source=1, depth_limit=3))
+    [(0, 1), (2, 1), (3, 2), (4, 3), (7, 2), (8, 7)]
+    >>> N = nx.DiGraph()
+    >>> nx.add_path(N, [0, 1, 2, 3, 4, 7])
+    >>> nx.add_path(N, [3, 5, 6, 7])
+    >>> sorted(nx.bfs_predecessors(N, source=2))
+    [(3, 2), (4, 3), (5, 3), (6, 5), (7, 4)]
+
+    Notes
+    -----
+    Based on http://www.ics.uci.edu/~eppstein/PADS/BFS.py
+    by D. Eppstein, July 2004. The modifications
+    to allow depth limits based on the Wikipedia article
+    "`Depth-limited-search`_".
+
+    .. _Depth-limited-search: https://en.wikipedia.org/wiki/Depth-limited_search
+
+    See Also
+    --------
+    bfs_tree
+    bfs_edges
+    edge_bfs
+    """
+    for s, t in bfs_edges(
+        G, source, depth_limit=depth_limit, sort_neighbors=sort_neighbors
+    ):
+        yield (t, s)
+
+
+@nx._dispatchable
+def bfs_successors(G, source, depth_limit=None, sort_neighbors=None):
+    """Returns an iterator of successors in breadth-first-search from source.
+
+    Parameters
+    ----------
+    G : NetworkX graph
+
+    source : node
+       Specify starting node for breadth-first search
+
+    depth_limit : int, optional(default=len(G))
+        Specify the maximum search depth
+
+    sort_neighbors : function (default=None)
+        A function that takes an iterator over nodes as the input, and
+        returns an iterable of the same nodes with a custom ordering.
+        For example, `sorted` will sort the nodes in increasing order.
+
+    Returns
+    -------
+    succ: iterator
+       (node, successors) iterator where `successors` is the non-empty list of
+       successors of `node` in a breadth first search from `source`.
+       To appear in the iterator, `node` must have successors.
+
+    Examples
+    --------
+    >>> G = nx.path_graph(3)
+    >>> dict(nx.bfs_successors(G, 0))
+    {0: [1], 1: [2]}
+    >>> H = nx.Graph()
+    >>> H.add_edges_from([(0, 1), (0, 2), (1, 3), (1, 4), (2, 5), (2, 6)])
+    >>> dict(nx.bfs_successors(H, 0))
+    {0: [1, 2], 1: [3, 4], 2: [5, 6]}
+    >>> G = nx.Graph()
+    >>> nx.add_path(G, [0, 1, 2, 3, 4, 5, 6])
+    >>> nx.add_path(G, [2, 7, 8, 9, 10])
+    >>> dict(nx.bfs_successors(G, source=1, depth_limit=3))
+    {1: [0, 2], 2: [3, 7], 3: [4], 7: [8]}
+    >>> G = nx.DiGraph()
+    >>> nx.add_path(G, [0, 1, 2, 3, 4, 5])
+    >>> dict(nx.bfs_successors(G, source=3))
+    {3: [4], 4: [5]}
+
+    Notes
+    -----
+    Based on http://www.ics.uci.edu/~eppstein/PADS/BFS.py
+    by D. Eppstein, July 2004.The modifications
+    to allow depth limits based on the Wikipedia article
+    "`Depth-limited-search`_".
+
+    .. _Depth-limited-search: https://en.wikipedia.org/wiki/Depth-limited_search
+
+    See Also
+    --------
+    bfs_tree
+    bfs_edges
+    edge_bfs
+    """
+    parent = source
+    children = []
+    for p, c in bfs_edges(
+        G, source, depth_limit=depth_limit, sort_neighbors=sort_neighbors
+    ):
+        if p == parent:
+            children.append(c)
+            continue
+        yield (parent, children)
+        children = [c]
+        parent = p
+    yield (parent, children)
+
+
+@nx._dispatchable
+def bfs_layers(G, sources):
+    """Returns an iterator of all the layers in breadth-first search traversal.
+
+    Parameters
+    ----------
+    G : NetworkX graph
+        A graph over which to find the layers using breadth-first search.
+
+    sources : node in `G` or list of nodes in `G`
+        Specify starting nodes for single source or multiple sources breadth-first search
+
+    Yields
+    ------
+    layer: list of nodes
+        Yields list of nodes at the same distance from sources
+
+    Examples
+    --------
+    >>> G = nx.path_graph(5)
+    >>> dict(enumerate(nx.bfs_layers(G, [0, 4])))
+    {0: [0, 4], 1: [1, 3], 2: [2]}
+    >>> H = nx.Graph()
+    >>> H.add_edges_from([(0, 1), (0, 2), (1, 3), (1, 4), (2, 5), (2, 6)])
+    >>> dict(enumerate(nx.bfs_layers(H, [1])))
+    {0: [1], 1: [0, 3, 4], 2: [2], 3: [5, 6]}
+    >>> dict(enumerate(nx.bfs_layers(H, [1, 6])))
+    {0: [1, 6], 1: [0, 3, 4, 2], 2: [5]}
+    """
+    if sources in G:
+        sources = [sources]
+
+    current_layer = list(sources)
+    visited = set(sources)
+
+    for source in current_layer:
+        if source not in G:
+            raise nx.NetworkXError(f"The node {source} is not in the graph.")
+
+    # this is basically BFS, except that the current layer only stores the nodes at
+    # same distance from sources at each iteration
+    while current_layer:
+        yield current_layer
+        next_layer = []
+        for node in current_layer:
+            for child in G[node]:
+                if child not in visited:
+                    visited.add(child)
+                    next_layer.append(child)
+        current_layer = next_layer
+
+
+REVERSE_EDGE = "reverse"
+TREE_EDGE = "tree"
+FORWARD_EDGE = "forward"
+LEVEL_EDGE = "level"
+
+
+@nx._dispatchable
+def bfs_labeled_edges(G, sources):
+    """Iterate over edges in a breadth-first search (BFS) labeled by type.
+
+    We generate triple of the form (*u*, *v*, *d*), where (*u*, *v*) is the
+    edge being explored in the breadth-first search and *d* is one of the
+    strings 'tree', 'forward', 'level', or 'reverse'.  A 'tree' edge is one in
+    which *v* is first discovered and placed into the layer below *u*.  A
+    'forward' edge is one in which *u* is on the layer above *v* and *v* has
+    already been discovered.  A 'level' edge is one in which both *u* and *v*
+    occur on the same layer.  A 'reverse' edge is one in which *u* is on a layer
+    below *v*.
+
+    We emit each edge exactly once.  In an undirected graph, 'reverse' edges do
+    not occur, because each is discovered either as a 'tree' or 'forward' edge.
+
+    Parameters
+    ----------
+    G : NetworkX graph
+        A graph over which to find the layers using breadth-first search.
+
+    sources : node in `G` or list of nodes in `G`
+        Starting nodes for single source or multiple sources breadth-first search
+
+    Yields
+    ------
+    edges: generator
+       A generator of triples (*u*, *v*, *d*) where (*u*, *v*) is the edge being
+       explored and *d* is described above.
+
+    Examples
+    --------
+    >>> G = nx.cycle_graph(4, create_using=nx.DiGraph)
+    >>> list(nx.bfs_labeled_edges(G, 0))
+    [(0, 1, 'tree'), (1, 2, 'tree'), (2, 3, 'tree'), (3, 0, 'reverse')]
+    >>> G = nx.complete_graph(3)
+    >>> list(nx.bfs_labeled_edges(G, 0))
+    [(0, 1, 'tree'), (0, 2, 'tree'), (1, 2, 'level')]
+    >>> list(nx.bfs_labeled_edges(G, [0, 1]))
+    [(0, 1, 'level'), (0, 2, 'tree'), (1, 2, 'forward')]
+    """
+    if sources in G:
+        sources = [sources]
+
+    neighbors = G._adj
+    directed = G.is_directed()
+    visited = set()
+    visit = visited.discard if directed else visited.add
+    # We use visited in a negative sense, so the visited set stays empty for the
+    # directed case and level edges are reported on their first occurrence in
+    # the undirected case.  Note our use of visited.discard -- this is built-in
+    # thus somewhat faster than a python-defined def nop(x): pass
+    depth = {s: 0 for s in sources}
+    queue = deque(depth.items())
+    push = queue.append
+    pop = queue.popleft
+    while queue:
+        u, du = pop()
+        for v in neighbors[u]:
+            if v not in depth:
+                depth[v] = dv = du + 1
+                push((v, dv))
+                yield u, v, TREE_EDGE
+            else:
+                dv = depth[v]
+                if du == dv:
+                    if v not in visited:
+                        yield u, v, LEVEL_EDGE
+                elif du < dv:
+                    yield u, v, FORWARD_EDGE
+                elif directed:
+                    yield u, v, REVERSE_EDGE
+        visit(u)
+
+
+@nx._dispatchable
+def descendants_at_distance(G, source, distance):
+    """Returns all nodes at a fixed `distance` from `source` in `G`.
+
+    Parameters
+    ----------
+    G : NetworkX graph
+        A graph
+    source : node in `G`
+    distance : the distance of the wanted nodes from `source`
+
+    Returns
+    -------
+    set()
+        The descendants of `source` in `G` at the given `distance` from `source`
+
+    Examples
+    --------
+    >>> G = nx.path_graph(5)
+    >>> nx.descendants_at_distance(G, 2, 2)
+    {0, 4}
+    >>> H = nx.DiGraph()
+    >>> H.add_edges_from([(0, 1), (0, 2), (1, 3), (1, 4), (2, 5), (2, 6)])
+    >>> nx.descendants_at_distance(H, 0, 2)
+    {3, 4, 5, 6}
+    >>> nx.descendants_at_distance(H, 5, 0)
+    {5}
+    >>> nx.descendants_at_distance(H, 5, 1)
+    set()
+    """
+    if source not in G:
+        raise nx.NetworkXError(f"The node {source} is not in the graph.")
+
+    bfs_generator = nx.bfs_layers(G, source)
+    for i, layer in enumerate(bfs_generator):
+        if i == distance:
+            return set(layer)
+    return set()

janus/lib/python3.10/site-packages/networkx/algorithms/traversal/depth_first_search.py

@@ -0,0 +1,529 @@
+"""Basic algorithms for depth-first searching the nodes of a graph."""
+
+from collections import defaultdict
+
+import networkx as nx
+
+__all__ = [
+    "dfs_edges",
+    "dfs_tree",
+    "dfs_predecessors",
+    "dfs_successors",
+    "dfs_preorder_nodes",
+    "dfs_postorder_nodes",
+    "dfs_labeled_edges",
+]
+
+
+@nx._dispatchable
+def dfs_edges(G, source=None, depth_limit=None, *, sort_neighbors=None):
+    """Iterate over edges in a depth-first-search (DFS).
+
+    Perform a depth-first-search over the nodes of `G` and yield
+    the edges in order. This may not generate all edges in `G`
+    (see `~networkx.algorithms.traversal.edgedfs.edge_dfs`).
+
+    Parameters
+    ----------
+    G : NetworkX graph
+
+    source : node, optional
+       Specify starting node for depth-first search and yield edges in
+       the component reachable from source.
+
+    depth_limit : int, optional (default=len(G))
+       Specify the maximum search depth.
+
+    sort_neighbors : function (default=None)
+        A function that takes an iterator over nodes as the input, and
+        returns an iterable of the same nodes with a custom ordering.
+        For example, `sorted` will sort the nodes in increasing order.
+
+    Yields
+    ------
+    edge: 2-tuple of nodes
+       Yields edges resulting from the depth-first-search.
+
+    Examples
+    --------
+    >>> G = nx.path_graph(5)
+    >>> list(nx.dfs_edges(G, source=0))
+    [(0, 1), (1, 2), (2, 3), (3, 4)]
+    >>> list(nx.dfs_edges(G, source=0, depth_limit=2))
+    [(0, 1), (1, 2)]
+
+    Notes
+    -----
+    If a source is not specified then a source is chosen arbitrarily and
+    repeatedly until all components in the graph are searched.
+
+    The implementation of this function is adapted from David Eppstein's
+    depth-first search function in PADS [1]_, with modifications
+    to allow depth limits based on the Wikipedia article
+    "Depth-limited search" [2]_.
+
+    See Also
+    --------
+    dfs_preorder_nodes
+    dfs_postorder_nodes
+    dfs_labeled_edges
+    :func:`~networkx.algorithms.traversal.edgedfs.edge_dfs`
+    :func:`~networkx.algorithms.traversal.breadth_first_search.bfs_edges`
+
+    References
+    ----------
+    .. [1] http://www.ics.uci.edu/~eppstein/PADS
+    .. [2] https://en.wikipedia.org/wiki/Depth-limited_search
+    """
+    if source is None:
+        # edges for all components
+        nodes = G
+    else:
+        # edges for components with source
+        nodes = [source]
+    if depth_limit is None:
+        depth_limit = len(G)
+
+    get_children = (
+        G.neighbors
+        if sort_neighbors is None
+        else lambda n: iter(sort_neighbors(G.neighbors(n)))
+    )
+
+    visited = set()
+    for start in nodes:
+        if start in visited:
+            continue
+        visited.add(start)
+        stack = [(start, get_children(start))]
+        depth_now = 1
+        while stack:
+            parent, children = stack[-1]
+            for child in children:
+                if child not in visited:
+                    yield parent, child
+                    visited.add(child)
+                    if depth_now < depth_limit:
+                        stack.append((child, get_children(child)))
+                        depth_now += 1
+                        break
+            else:
+                stack.pop()
+                depth_now -= 1
+
+
+@nx._dispatchable(returns_graph=True)
+def dfs_tree(G, source=None, depth_limit=None, *, sort_neighbors=None):
+    """Returns oriented tree constructed from a depth-first-search from source.
+
+    Parameters
+    ----------
+    G : NetworkX graph
+
+    source : node, optional
+       Specify starting node for depth-first search.
+
+    depth_limit : int, optional (default=len(G))
+       Specify the maximum search depth.
+
+    sort_neighbors : function (default=None)
+        A function that takes an iterator over nodes as the input, and
+        returns an iterable of the same nodes with a custom ordering.
+        For example, `sorted` will sort the nodes in increasing order.
+
+    Returns
+    -------
+    T : NetworkX DiGraph
+       An oriented tree
+
+    Examples
+    --------
+    >>> G = nx.path_graph(5)
+    >>> T = nx.dfs_tree(G, source=0, depth_limit=2)
+    >>> list(T.edges())
+    [(0, 1), (1, 2)]
+    >>> T = nx.dfs_tree(G, source=0)
+    >>> list(T.edges())
+    [(0, 1), (1, 2), (2, 3), (3, 4)]
+
+    See Also
+    --------
+    dfs_preorder_nodes
+    dfs_postorder_nodes
+    dfs_labeled_edges
+    :func:`~networkx.algorithms.traversal.edgedfs.edge_dfs`
+    :func:`~networkx.algorithms.traversal.breadth_first_search.bfs_tree`
+    """
+    T = nx.DiGraph()
+    if source is None:
+        T.add_nodes_from(G)
+    else:
+        T.add_node(source)
+    T.add_edges_from(dfs_edges(G, source, depth_limit, sort_neighbors=sort_neighbors))
+    return T
+
+
+@nx._dispatchable
+def dfs_predecessors(G, source=None, depth_limit=None, *, sort_neighbors=None):
+    """Returns dictionary of predecessors in depth-first-search from source.
+
+    Parameters
+    ----------
+    G : NetworkX graph
+
+    source : node, optional
+       Specify starting node for depth-first search.
+       Note that you will get predecessors for all nodes in the
+       component containing `source`. This input only specifies
+       where the DFS starts.
+
+    depth_limit : int, optional (default=len(G))
+       Specify the maximum search depth.
+
+    sort_neighbors : function (default=None)
+        A function that takes an iterator over nodes as the input, and
+        returns an iterable of the same nodes with a custom ordering.
+        For example, `sorted` will sort the nodes in increasing order.
+
+    Returns
+    -------
+    pred: dict
+       A dictionary with nodes as keys and predecessor nodes as values.
+
+    Examples
+    --------
+    >>> G = nx.path_graph(4)
+    >>> nx.dfs_predecessors(G, source=0)
+    {1: 0, 2: 1, 3: 2}
+    >>> nx.dfs_predecessors(G, source=0, depth_limit=2)
+    {1: 0, 2: 1}
+
+    Notes
+    -----
+    If a source is not specified then a source is chosen arbitrarily and
+    repeatedly until all components in the graph are searched.
+
+    The implementation of this function is adapted from David Eppstein's
+    depth-first search function in `PADS`_, with modifications
+    to allow depth limits based on the Wikipedia article
+    "`Depth-limited search`_".
+
+    .. _PADS: http://www.ics.uci.edu/~eppstein/PADS
+    .. _Depth-limited search: https://en.wikipedia.org/wiki/Depth-limited_search
+
+    See Also
+    --------
+    dfs_preorder_nodes
+    dfs_postorder_nodes
+    dfs_labeled_edges
+    :func:`~networkx.algorithms.traversal.edgedfs.edge_dfs`
+    :func:`~networkx.algorithms.traversal.breadth_first_search.bfs_tree`
+    """
+    return {
+        t: s
+        for s, t in dfs_edges(G, source, depth_limit, sort_neighbors=sort_neighbors)
+    }
+
+
+@nx._dispatchable
+def dfs_successors(G, source=None, depth_limit=None, *, sort_neighbors=None):
+    """Returns dictionary of successors in depth-first-search from source.
+
+    Parameters
+    ----------
+    G : NetworkX graph
+
+    source : node, optional
+       Specify starting node for depth-first search.
+       Note that you will get successors for all nodes in the
+       component containing `source`. This input only specifies
+       where the DFS starts.
+
+    depth_limit : int, optional (default=len(G))
+       Specify the maximum search depth.
+
+    sort_neighbors : function (default=None)
+        A function that takes an iterator over nodes as the input, and
+        returns an iterable of the same nodes with a custom ordering.
+        For example, `sorted` will sort the nodes in increasing order.
+
+    Returns
+    -------
+    succ: dict
+       A dictionary with nodes as keys and list of successor nodes as values.
+
+    Examples
+    --------
+    >>> G = nx.path_graph(5)
+    >>> nx.dfs_successors(G, source=0)
+    {0: [1], 1: [2], 2: [3], 3: [4]}
+    >>> nx.dfs_successors(G, source=0, depth_limit=2)
+    {0: [1], 1: [2]}
+
+    Notes
+    -----
+    If a source is not specified then a source is chosen arbitrarily and
+    repeatedly until all components in the graph are searched.
+
+    The implementation of this function is adapted from David Eppstein's
+    depth-first search function in `PADS`_, with modifications
+    to allow depth limits based on the Wikipedia article
+    "`Depth-limited search`_".
+
+    .. _PADS: http://www.ics.uci.edu/~eppstein/PADS
+    .. _Depth-limited search: https://en.wikipedia.org/wiki/Depth-limited_search
+
+    See Also
+    --------
+    dfs_preorder_nodes
+    dfs_postorder_nodes
+    dfs_labeled_edges
+    :func:`~networkx.algorithms.traversal.edgedfs.edge_dfs`
+    :func:`~networkx.algorithms.traversal.breadth_first_search.bfs_tree`
+    """
+    d = defaultdict(list)
+    for s, t in dfs_edges(
+        G,
+        source=source,
+        depth_limit=depth_limit,
+        sort_neighbors=sort_neighbors,
+    ):
+        d[s].append(t)
+    return dict(d)
+
+
+@nx._dispatchable
+def dfs_postorder_nodes(G, source=None, depth_limit=None, *, sort_neighbors=None):
+    """Generate nodes in a depth-first-search post-ordering starting at source.
+
+    Parameters
+    ----------
+    G : NetworkX graph
+
+    source : node, optional
+       Specify starting node for depth-first search.
+
+    depth_limit : int, optional (default=len(G))
+       Specify the maximum search depth.
+
+    sort_neighbors : function (default=None)
+        A function that takes an iterator over nodes as the input, and
+        returns an iterable of the same nodes with a custom ordering.
+        For example, `sorted` will sort the nodes in increasing order.
+
+    Returns
+    -------
+    nodes: generator
+       A generator of nodes in a depth-first-search post-ordering.
+
+    Examples
+    --------
+    >>> G = nx.path_graph(5)
+    >>> list(nx.dfs_postorder_nodes(G, source=0))
+    [4, 3, 2, 1, 0]
+    >>> list(nx.dfs_postorder_nodes(G, source=0, depth_limit=2))
+    [1, 0]
+
+    Notes
+    -----
+    If a source is not specified then a source is chosen arbitrarily and
+    repeatedly until all components in the graph are searched.
+
+    The implementation of this function is adapted from David Eppstein's
+    depth-first search function in `PADS`_, with modifications
+    to allow depth limits based on the Wikipedia article
+    "`Depth-limited search`_".
+
+    .. _PADS: http://www.ics.uci.edu/~eppstein/PADS
+    .. _Depth-limited search: https://en.wikipedia.org/wiki/Depth-limited_search
+
+    See Also
+    --------
+    dfs_edges
+    dfs_preorder_nodes
+    dfs_labeled_edges
+    :func:`~networkx.algorithms.traversal.edgedfs.edge_dfs`
+    :func:`~networkx.algorithms.traversal.breadth_first_search.bfs_tree`
+    """
+    edges = nx.dfs_labeled_edges(
+        G, source=source, depth_limit=depth_limit, sort_neighbors=sort_neighbors
+    )
+    return (v for u, v, d in edges if d == "reverse")
+
+
+@nx._dispatchable
+def dfs_preorder_nodes(G, source=None, depth_limit=None, *, sort_neighbors=None):
+    """Generate nodes in a depth-first-search pre-ordering starting at source.
+
+    Parameters
+    ----------
+    G : NetworkX graph
+
+    source : node, optional
+       Specify starting node for depth-first search and return nodes in
+       the component reachable from source.
+
+    depth_limit : int, optional (default=len(G))
+       Specify the maximum search depth.
+
+    sort_neighbors : function (default=None)
+        A function that takes an iterator over nodes as the input, and
+        returns an iterable of the same nodes with a custom ordering.
+        For example, `sorted` will sort the nodes in increasing order.
+
+    Returns
+    -------
+    nodes: generator
+       A generator of nodes in a depth-first-search pre-ordering.
+
+    Examples
+    --------
+    >>> G = nx.path_graph(5)
+    >>> list(nx.dfs_preorder_nodes(G, source=0))
+    [0, 1, 2, 3, 4]
+    >>> list(nx.dfs_preorder_nodes(G, source=0, depth_limit=2))
+    [0, 1, 2]
+
+    Notes
+    -----
+    If a source is not specified then a source is chosen arbitrarily and
+    repeatedly until all components in the graph are searched.
+
+    The implementation of this function is adapted from David Eppstein's
+    depth-first search function in `PADS`_, with modifications
+    to allow depth limits based on the Wikipedia article
+    "`Depth-limited search`_".
+
+    .. _PADS: http://www.ics.uci.edu/~eppstein/PADS
+    .. _Depth-limited search: https://en.wikipedia.org/wiki/Depth-limited_search
+
+    See Also
+    --------
+    dfs_edges
+    dfs_postorder_nodes
+    dfs_labeled_edges
+    :func:`~networkx.algorithms.traversal.breadth_first_search.bfs_edges`
+    """
+    edges = nx.dfs_labeled_edges(
+        G, source=source, depth_limit=depth_limit, sort_neighbors=sort_neighbors
+    )
+    return (v for u, v, d in edges if d == "forward")
+
+
+@nx._dispatchable
+def dfs_labeled_edges(G, source=None, depth_limit=None, *, sort_neighbors=None):
+    """Iterate over edges in a depth-first-search (DFS) labeled by type.
+
+    Parameters
+    ----------
+    G : NetworkX graph
+
+    source : node, optional
+       Specify starting node for depth-first search and return edges in
+       the component reachable from source.
+
+    depth_limit : int, optional (default=len(G))
+       Specify the maximum search depth.
+
+    sort_neighbors : function (default=None)
+        A function that takes an iterator over nodes as the input, and
+        returns an iterable of the same nodes with a custom ordering.
+        For example, `sorted` will sort the nodes in increasing order.
+
+    Returns
+    -------
+    edges: generator
+       A generator of triples of the form (*u*, *v*, *d*), where (*u*,
+       *v*) is the edge being explored in the depth-first search and *d*
+       is one of the strings 'forward', 'nontree', 'reverse', or 'reverse-depth_limit'.
+       A 'forward' edge is one in which *u* has been visited but *v* has
+       not. A 'nontree' edge is one in which both *u* and *v* have been
+       visited but the edge is not in the DFS tree. A 'reverse' edge is
+       one in which both *u* and *v* have been visited and the edge is in
+       the DFS tree. When the `depth_limit` is reached via a 'forward' edge,
+       a 'reverse' edge is immediately generated rather than the subtree
+       being explored. To indicate this flavor of 'reverse' edge, the string
+       yielded is 'reverse-depth_limit'.
+
+    Examples
+    --------
+
+    The labels reveal the complete transcript of the depth-first search
+    algorithm in more detail than, for example, :func:`dfs_edges`::
+
+        >>> from pprint import pprint
+        >>>
+        >>> G = nx.DiGraph([(0, 1), (1, 2), (2, 1)])
+        >>> pprint(list(nx.dfs_labeled_edges(G, source=0)))
+        [(0, 0, 'forward'),
+         (0, 1, 'forward'),
+         (1, 2, 'forward'),
+         (2, 1, 'nontree'),
+         (1, 2, 'reverse'),
+         (0, 1, 'reverse'),
+         (0, 0, 'reverse')]
+
+    Notes
+    -----
+    If a source is not specified then a source is chosen arbitrarily and
+    repeatedly until all components in the graph are searched.
+
+    The implementation of this function is adapted from David Eppstein's
+    depth-first search function in `PADS`_, with modifications
+    to allow depth limits based on the Wikipedia article
+    "`Depth-limited search`_".
+
+    .. _PADS: http://www.ics.uci.edu/~eppstein/PADS
+    .. _Depth-limited search: https://en.wikipedia.org/wiki/Depth-limited_search
+
+    See Also
+    --------
+    dfs_edges
+    dfs_preorder_nodes
+    dfs_postorder_nodes
+    """
+    # Based on http://www.ics.uci.edu/~eppstein/PADS/DFS.py
+    # by D. Eppstein, July 2004.
+    if source is None:
+        # edges for all components
+        nodes = G
+    else:
+        # edges for components with source
+        nodes = [source]
+    if depth_limit is None:
+        depth_limit = len(G)
+
+    get_children = (
+        G.neighbors
+        if sort_neighbors is None
+        else lambda n: iter(sort_neighbors(G.neighbors(n)))
+    )
+
+    visited = set()
+    for start in nodes:
+        if start in visited:
+            continue
+        yield start, start, "forward"
+        visited.add(start)
+        stack = [(start, get_children(start))]
+        depth_now = 1
+        while stack:
+            parent, children = stack[-1]
+            for child in children:
+                if child in visited:
+                    yield parent, child, "nontree"
+                else:
+                    yield parent, child, "forward"
+                    visited.add(child)
+                    if depth_now < depth_limit:
+                        stack.append((child, iter(get_children(child))))
+                        depth_now += 1
+                        break
+                    else:
+                        yield parent, child, "reverse-depth_limit"
+            else:
+                stack.pop()
+                depth_now -= 1
+                if stack:
+                    yield stack[-1][0], parent, "reverse"
+        yield start, start, "reverse"

janus/lib/python3.10/site-packages/networkx/algorithms/traversal/edgebfs.py

@@ -0,0 +1,178 @@
+"""
+=============================
+Breadth First Search on Edges
+=============================
+
+Algorithms for a breadth-first traversal of edges in a graph.
+
+"""
+
+from collections import deque
+
+import networkx as nx
+
+FORWARD = "forward"
+REVERSE = "reverse"
+
+__all__ = ["edge_bfs"]
+
+
+@nx._dispatchable
+def edge_bfs(G, source=None, orientation=None):
+    """A directed, breadth-first-search of edges in `G`, beginning at `source`.
+
+    Yield the edges of G in a breadth-first-search order continuing until
+    all edges are generated.
+
+    Parameters
+    ----------
+    G : graph
+        A directed/undirected graph/multigraph.
+
+    source : node, list of nodes
+        The node from which the traversal begins. If None, then a source
+        is chosen arbitrarily and repeatedly until all edges from each node in
+        the graph are searched.
+
+    orientation : None | 'original' | 'reverse' | 'ignore' (default: None)
+        For directed graphs and directed multigraphs, edge traversals need not
+        respect the original orientation of the edges.
+        When set to 'reverse' every edge is traversed in the reverse direction.
+        When set to 'ignore', every edge is treated as undirected.
+        When set to 'original', every edge is treated as directed.
+        In all three cases, the yielded edge tuples add a last entry to
+        indicate the direction in which that edge was traversed.
+        If orientation is None, the yielded edge has no direction indicated.
+        The direction is respected, but not reported.
+
+    Yields
+    ------
+    edge : directed edge
+        A directed edge indicating the path taken by the breadth-first-search.
+        For graphs, `edge` is of the form `(u, v)` where `u` and `v`
+        are the tail and head of the edge as determined by the traversal.
+        For multigraphs, `edge` is of the form `(u, v, key)`, where `key` is
+        the key of the edge. When the graph is directed, then `u` and `v`
+        are always in the order of the actual directed edge.
+        If orientation is not None then the edge tuple is extended to include
+        the direction of traversal ('forward' or 'reverse') on that edge.
+
+    Examples
+    --------
+    >>> nodes = [0, 1, 2, 3]
+    >>> edges = [(0, 1), (1, 0), (1, 0), (2, 0), (2, 1), (3, 1)]
+
+    >>> list(nx.edge_bfs(nx.Graph(edges), nodes))
+    [(0, 1), (0, 2), (1, 2), (1, 3)]
+
+    >>> list(nx.edge_bfs(nx.DiGraph(edges), nodes))
+    [(0, 1), (1, 0), (2, 0), (2, 1), (3, 1)]
+
+    >>> list(nx.edge_bfs(nx.MultiGraph(edges), nodes))
+    [(0, 1, 0), (0, 1, 1), (0, 1, 2), (0, 2, 0), (1, 2, 0), (1, 3, 0)]
+
+    >>> list(nx.edge_bfs(nx.MultiDiGraph(edges), nodes))
+    [(0, 1, 0), (1, 0, 0), (1, 0, 1), (2, 0, 0), (2, 1, 0), (3, 1, 0)]
+
+    >>> list(nx.edge_bfs(nx.DiGraph(edges), nodes, orientation="ignore"))
+    [(0, 1, 'forward'), (1, 0, 'reverse'), (2, 0, 'reverse'), (2, 1, 'reverse'), (3, 1, 'reverse')]
+
+    >>> list(nx.edge_bfs(nx.MultiDiGraph(edges), nodes, orientation="ignore"))
+    [(0, 1, 0, 'forward'), (1, 0, 0, 'reverse'), (1, 0, 1, 'reverse'), (2, 0, 0, 'reverse'), (2, 1, 0, 'reverse'), (3, 1, 0, 'reverse')]
+
+    Notes
+    -----
+    The goal of this function is to visit edges. It differs from the more
+    familiar breadth-first-search of nodes, as provided by
+    :func:`networkx.algorithms.traversal.breadth_first_search.bfs_edges`, in
+    that it does not stop once every node has been visited. In a directed graph
+    with edges [(0, 1), (1, 2), (2, 1)], the edge (2, 1) would not be visited
+    if not for the functionality provided by this function.
+
+    The naming of this function is very similar to bfs_edges. The difference
+    is that 'edge_bfs' yields edges even if they extend back to an already
+    explored node while 'bfs_edges' yields the edges of the tree that results
+    from a breadth-first-search (BFS) so no edges are reported if they extend
+    to already explored nodes. That means 'edge_bfs' reports all edges while
+    'bfs_edges' only report those traversed by a node-based BFS. Yet another
+    description is that 'bfs_edges' reports the edges traversed during BFS
+    while 'edge_bfs' reports all edges in the order they are explored.
+
+    See Also
+    --------
+    bfs_edges
+    bfs_tree
+    edge_dfs
+
+    """
+    nodes = list(G.nbunch_iter(source))
+    if not nodes:
+        return
+
+    directed = G.is_directed()
+    kwds = {"data": False}
+    if G.is_multigraph() is True:
+        kwds["keys"] = True
+
+    # set up edge lookup
+    if orientation is None:
+
+        def edges_from(node):
+            return iter(G.edges(node, **kwds))
+
+    elif not directed or orientation == "original":
+
+        def edges_from(node):
+            for e in G.edges(node, **kwds):
+                yield e + (FORWARD,)
+
+    elif orientation == "reverse":
+
+        def edges_from(node):
+            for e in G.in_edges(node, **kwds):
+                yield e + (REVERSE,)
+
+    elif orientation == "ignore":
+
+        def edges_from(node):
+            for e in G.edges(node, **kwds):
+                yield e + (FORWARD,)
+            for e in G.in_edges(node, **kwds):
+                yield e + (REVERSE,)
+
+    else:
+        raise nx.NetworkXError("invalid orientation argument.")
+
+    if directed:
+        neighbors = G.successors
+
+        def edge_id(edge):
+            # remove direction indicator
+            return edge[:-1] if orientation is not None else edge
+
+    else:
+        neighbors = G.neighbors
+
+        def edge_id(edge):
+            return (frozenset(edge[:2]),) + edge[2:]
+
+    check_reverse = directed and orientation in ("reverse", "ignore")
+
+    # start BFS
+    visited_nodes = set(nodes)
+    visited_edges = set()
+    queue = deque([(n, edges_from(n)) for n in nodes])
+    while queue:
+        parent, children_edges = queue.popleft()
+        for edge in children_edges:
+            if check_reverse and edge[-1] == REVERSE:
+                child = edge[0]
+            else:
+                child = edge[1]
+            if child not in visited_nodes:
+                visited_nodes.add(child)
+                queue.append((child, edges_from(child)))
+            edgeid = edge_id(edge)
+            if edgeid not in visited_edges:
+                visited_edges.add(edgeid)
+                yield edge