source/train.py

import itertools
import random
import os
import time
import torch
import math
import inspect
import torch.nn as nn
import torch.nn.functional as F
import numpy as np
import json
from tqdm import tqdm
import loguru
import shutil


# model architecture


class Head(nn.Module):
    """One head of self-attention."""

    def __init__(self, head_size, n_embd, dropout, block_size):
        super().__init__()
        self.head_size = head_size
        self.key = nn.Linear(n_embd, head_size, bias=False)
        self.query = nn.Linear(n_embd, head_size, bias=False)
        self.value = nn.Linear(n_embd, head_size, bias=False)
        self.pos_embeds = nn.Embedding(block_size, head_size)
        self.attn_dropout = nn.Dropout(dropout)
        self.register_buffer(
            "pos_embeds_indices",
            torch.arange(0, block_size, 1, dtype=torch.int64)
        )
        self.register_buffer(
            "causal_mask",
            (torch.tril(torch.ones((block_size, block_size), dtype=torch.bool)) == False)
        )
    # ======


    def forward(self, x):
        B, T, C = x.shape
        k = self.key(x)  # (B, T, C)
        q = self.query(x)  # (B, T, C)
        v = self.value(x)  # (B, T, C)
        r = self.pos_embeds(self.pos_embeds_indices[-T:])  # (T, C)
        s_rel = q @ r.t()  # (B, T, T)
        s_rel = F.pad(s_rel, (1, 0))  # (B, T, 1+T)
        s_rel = s_rel.reshape(B, s_rel.shape[-1], s_rel.shape[-2])  # (B, 1+T, T)
        s_rel = s_rel[:, 1:, :]  # (B, T, T)
        attn = ((q @ k.transpose(-2, -1)) + s_rel) * (self.head_size**-0.5)  # (B, T, T)
        attn = attn.masked_fill(self.causal_mask[:T, :T], float("-inf"))  # (B, T, T)
        attn = F.softmax(attn, dim=-1)  # (B, T, T)
        attn = self.attn_dropout(attn)  # (B, T, T)
        out = attn @ v  # (B, T, C)

        return out
    # ======
# ======


class MultiHeadAttention(nn.Module):
    """Multiple heads of self-attention in parallel."""

    def __init__(self, num_heads, head_size, n_embd, dropout, block_size):
        super().__init__()
        self.heads = nn.ModuleList([Head(head_size, n_embd, dropout, block_size) for _ in range(num_heads)])
        self.proj = nn.Linear(n_embd, n_embd)
        self.dropout = nn.Dropout(dropout)
    # ======


    def forward(self, x):
        out = torch.cat([h(x) for h in self.heads], dim=-1)
        out = self.dropout(self.proj(out))
        return out
    # ======
# ======


class FeedForward(nn.Module):
    """A simple linear layer followed by a non-linearity."""

    def __init__(self, n_embd, ff_width, dropout):
        super().__init__()
        self.net = nn.Sequential(
            nn.Linear(n_embd, ff_width * n_embd, bias=False),
            nn.SiLU(),
            nn.Linear(ff_width * n_embd, n_embd, bias=False),
            nn.Dropout(dropout),
        )
    # ======


    def forward(self, x):
        return self.net(x)
    # ======
# ======


class Block(nn.Module):
    """Transformer block: communication followed by feedforward."""

    def __init__(self, n_embd, n_head, ff_width, dropout, block_size):
        super().__init__()
        head_size = n_embd // n_head
        self.sa = MultiHeadAttention(n_head, head_size, n_embd, dropout, block_size)
        self.ffwd = FeedForward(n_embd, ff_width, dropout)
        self.ln1 = nn.RMSNorm(normalized_shape=n_embd, eps=1e-5)
        self.ln2 = nn.RMSNorm(normalized_shape=n_embd, eps=1e-5)
    # ======


    def forward(self, x):
        x = x + self.sa(self.ln1(x))
        x = x + self.ffwd(self.ln2(x))
        return x
    # ======
# ======


class GPT(nn.Module):
    """Transformer architecture for flowshop scheduling."""

    def __init__(self, intermediate_schedules, vocab_size, n_embd, n_head, n_layer, dropout, ff_width, block_size):
        super().__init__()
        self.jobs_embedding_table = nn.Embedding(vocab_size, n_embd)
        self.blocks = nn.Sequential(*[Block(n_embd=n_embd, n_head=n_head, ff_width=ff_width, dropout=dropout, block_size=block_size) for _ in range(n_layer)])
        self.ln_f = nn.LayerNorm(n_embd)
        self.makespan_head = nn.Linear(n_embd, 1)
        self.intermediate_schedules = intermediate_schedules
    # ======


    def forward(self, idx, targets):
        B, T = idx.shape

        # idx and targets are both (B,T,) tensor of integers
        x = self.jobs_embedding_table(idx)  # (B,T,C,)
        x = self.blocks(x)  # (B,T,C,)
        x = self.ln_f(x)  # (B,T,C,)
        if not self.intermediate_schedules:
            x = x[:, -1, :].squeeze()  # (B,C,)
            makespans = self.makespan_head(x).squeeze()  # (B,)
            targets = targets[:,-1].squeeze() # (B,)
        else:
            x = x.reshape(B*T, -1)  # (B*T,C)
            makespans = self.makespan_head(x).squeeze()  # (B*T,)
            targets = targets.reshape(B*T)  # (B*T,)
        # ======
        loss = F.smooth_l1_loss(makespans, targets, beta=0.1)
        return makespans, loss
    # ======


    def generate(self, job_embeds):
        """
        Function to generate Transformer predicted makespan from input schedule of job embeddings.
        Input:
            - job_embeds: a (T,C,) tensor of job embeddings
        Output:
            - makespan: a scalar tensor of the predicted makespan
        """

        job_embeds = job_embeds.unsqueeze(0) # (1,T,C)
        x = self.blocks(job_embeds)  # (1,T,C,)
        x = self.ln_f(x)  # (1,T,C,)
        makespans = self.makespan_head(x).squeeze()  # (T,)
        makespan = makespans[-1]

        return makespan
    # ======


def train(
    testing: bool,
    seed: int,
    data_dir: str,
    n_embd: int,
    n_head: int,
    n_layer: int,
    intermediate_schedules: bool,
    dropout: float,
    ff_width: int,
    train_batch_size: int,
    val_batch_size: int,
    nb_epochs: int,
    early_stopping_patience: int,
    checkpoint_interval_ratio: float,
    decay_lr: bool,
    lr_partitions_ratios: list[float],
    init_lr: float,
    max_lr: float,
    min_lr: float,
    lr_warmup_iters_ratio: float,
    lr_decay_iters_ratio: float,
    beta1: float,
    beta2: float,
    weight_decay: float,
    grad_clip: float,
    compile: bool,
    compile_mode: str,
    save_only_last_checkpoint: bool,
    output_dir: str,
):

    os.makedirs(output_dir, exist_ok=True)

    # check if experiment termination flag file exists
    if not testing:
        if os.path.exists(os.path.join(output_dir, ".terminated_phase1")):
            print("Phase 1 already terminated. Exiting...")
            return
        # ======
        if not os.path.exists(os.path.join(output_dir, "viz_train.ipynb")):
            shutil.copy("viz_train.ipynb", output_dir)
        # ======
    else:

        # delete all the files that are created by this script like log files, batch_losses.npy and so on ...
        files_to_delete = [
            "train.log",
            "train_parameters.json",
            "batch_losses.npy",
            "last_batch_loss_idx.npy",
            "val_losses.npy",
            "last_val_loss_idx.npy",
            "train_pbar_epoch.log",
            "train_pbar_val.log",
            ".terminated_phase1",
            "viz_train.ipynb",
        ]
        for f in files_to_delete:
            f_path = os.path.join(output_dir, f)
            if os.path.exists(f_path): os.remove(f_path)
        # ======
        checkpoints_dir = os.path.join(output_dir, "checkpoints")
        if os.path.exists(checkpoints_dir): shutil.rmtree(checkpoints_dir)
        shutil.copy("viz_train.ipynb", output_dir)
    # ======

    # check if GPU is available
    assert torch.cuda.is_available(), "This code requires a GPU to run. Please run it on a machine with a CUDA-compatible GPU."
    device = "cuda"

    # setup logging
    loguru.logger.add(os.path.join(output_dir, "train.log"))

    # set random seeds
    torch.manual_seed(seed)
    random.seed(seed)
    np.random.seed(seed)

    # setup model architecture parameters
    with open(os.path.join(data_dir, "metadata.json"), "r") as f:
        metadata = json.load(f)
    block_size = metadata["nb_jobs"]  # context window size
    vocab_size = metadata["nb_jobs"]  # vocabulary size
    n_embd = n_embd  # embedding dimension
    n_head = n_head  # number of attention heads
    assert n_embd % n_head == 0
    n_layer = n_layer  # number of transformer blocks
    intermediate_schedules = intermediate_schedules
    ff_width = ff_width

    # setup training parameters and utils
    train_batch_size = train_batch_size  # batch size for training
    val_batch_size = val_batch_size # batch size for validation
    nb_epochs = nb_epochs # number of pseudo-epochs to train for
    early_stopping_patience = early_stopping_patience  # number of epochs without improvement to trigger early stopping
    dropout = dropout


    class FlowshopDataset(torch.utils.data.Dataset):
        """Dataset for flowshop scheduling problem."""

        def __init__(self, dataset_path, split, load_in_memory=True):
            metadata_path = os.path.join(dataset_path, "metadata.json")
            with open(metadata_path, "r") as f:
                metadata = json.load(f)
            nb_samples = metadata["nb_samples"]
            nb_jobs = metadata["nb_jobs"]
            schedules_path = os.path.join(dataset_path, f"schedules_{split}.npy")
            schedules = np.lib.format.open_memmap(
                schedules_path, dtype=np.int32, mode="r", shape=(nb_samples, nb_jobs)
            )
            loguru.logger.info(f"Loaded schedules from {schedules_path} with shape {schedules.shape}")
            makespans_path = os.path.join(dataset_path, f"makespans_{split}.npy")
            makespans = np.lib.format.open_memmap(
                makespans_path, dtype=np.float32, mode="r", shape=(nb_samples,)
            )
            loguru.logger.info(f"Loaded makespans from {makespans_path} with shape {makespans.shape}")
            if load_in_memory:
                schedules = np.array(schedules)
                makespans = np.array(makespans)
            self.schedules = torch.from_numpy(schedules)
            self.makespans = torch.from_numpy(makespans)
        # ======


        def __len__(self):
            return len(self.schedules)
        # ======


        def __getitem__(self, idx):
            return self.schedules[idx], self.makespans[idx]
        # ======


    train_dataset = FlowshopDataset(data_dir, split="train", load_in_memory=True)
    train_data_loader = torch.utils.data.DataLoader(
        train_dataset,
        batch_size=train_batch_size,
        shuffle=False,
        drop_last=False,
    )
    ## log the shape of the items returned by the train_data_loader
    for schedules, makespans in train_data_loader:
        loguru.logger.info(f"schedules.shape: {schedules.shape}")
        loguru.logger.info(f"makespans.shape: {makespans.shape}")
        break
    nb_iters = nb_epochs * len(train_data_loader)
    checkpoint_interval = int(checkpoint_interval_ratio * len(train_data_loader))
    decay_lr = decay_lr
    lr_partitions_ratios = lr_partitions_ratios + [None]
    lr_partitions_iters = [int(r * nb_iters) for r in lr_partitions_ratios[:-1]]
    lr_partitions_iters = lr_partitions_iters + [nb_iters - sum(lr_partitions_iters)]
    assert sum(lr_partitions_iters) == nb_iters
    init_lr = init_lr #1e-4
    max_lr = max_lr #1e-3
    min_lr = min_lr #5*1e-5
    lr_warmup_iters_ratio = lr_warmup_iters_ratio #0.1
    lr_decay_iters_ratio = lr_decay_iters_ratio #0.95
    beta1 = beta1 # Adam beta1
    beta2 = beta2 # Adam beta2
    weight_decay = weight_decay # 1e-1  # weight decay
    grad_clip = grad_clip # 1.0  # gradient clipping value
    compile = compile
    compile_mode = compile_mode
    save_only_last_checkpoint = save_only_last_checkpoint


    def human_readable(num):
        """Define function to make large numbers of parameters human-readable."""

        magnitude = 0
        while abs(num) >= 1000:
            magnitude += 1
            num /= 1000.0
        return "%.0f%s" % (num, ["", "K", "M", "G", "T", "P"][magnitude])
    # ======


    def get_lr(it):
        """Get the learning rate for the current iteration."""

        i = 0
        tmp_it = it - lr_partitions_iters[i]
        while tmp_it >= 0:
            i += 1
            tmp_it -= lr_partitions_iters[i]

        lr_partition_iters = lr_partitions_iters[i]
        warmup_iters = int(lr_partition_iters * lr_warmup_iters_ratio)
        lr_decay_iters = int(lr_partition_iters * lr_decay_iters_ratio)

        it = it - sum(lr_partitions_iters[:i])
    
        # 1) linear warmup for warmup_iters steps
        if it < warmup_iters:
            return (it / warmup_iters) * (max_lr - init_lr) + init_lr
        
        # 2) if it > lr_decay_iters, return min learning rate
        if it > lr_decay_iters:
            return min_lr
        
        # 3) in between, use cosine decay down to min learning rate
        decay_ratio = (it - warmup_iters) / (lr_decay_iters - warmup_iters)
        assert 0 <= decay_ratio <= 1
        coeff = 0.5 * (1.0 + math.cos(math.pi * decay_ratio))  # coeff ranges 0..1
        return min_lr + coeff * (max_lr - min_lr)
    # ======


    # log parameters
    loguru.logger.info(f"data_dir: {data_dir}")
    loguru.logger.info(f"block_size: {block_size}")
    loguru.logger.info(f"vocab_size: {vocab_size}")
    loguru.logger.info(f"n_embd: {n_embd}")
    loguru.logger.info(f"n_head: {n_head}")
    loguru.logger.info(f"n_layer: {n_layer}")
    loguru.logger.info(f"ff_width: {ff_width}")
    loguru.logger.info(f"train_batch_size: {train_batch_size}")
    loguru.logger.info(f"val_batch_size: {val_batch_size}")
    loguru.logger.info(f"dropout: {dropout}")
    loguru.logger.info(f"nb_epochs: {nb_epochs}")
    loguru.logger.info(f"early_stopping_patience: {early_stopping_patience}")
    loguru.logger.info(f"nb_iters: {nb_iters}")
    loguru.logger.info(f"checkpoint_interval: {checkpoint_interval}")
    loguru.logger.info(f"decay_lr: {decay_lr}")
    loguru.logger.info(f"lr_partitions_ratios: {lr_partitions_ratios}")
    loguru.logger.info(f"lr_partitions_iters: {lr_partitions_iters}")
    loguru.logger.info(f"init_lr: {init_lr}")
    loguru.logger.info(f"max_lr: {max_lr}")
    loguru.logger.info(f"min_lr: {min_lr}")
    loguru.logger.info(f"lr_warmup_iters_ratio: {lr_warmup_iters_ratio}")
    loguru.logger.info(f"lr_decay_iters_ratio: {lr_decay_iters_ratio}")
    loguru.logger.info(f"beta1: {beta1}")
    loguru.logger.info(f"beta2: {beta2}")
    loguru.logger.info(f"weight_decay: {weight_decay}")
    loguru.logger.info(f"grad_clip: {grad_clip}")
    loguru.logger.info(f"compile: {compile}")
    loguru.logger.info(f"compile_mode: {compile_mode}")
    loguru.logger.info(f"intermediate_schedules: {intermediate_schedules}")
    loguru.logger.info(f"save_only_last_checkpoint: {save_only_last_checkpoint}")

    # save parameters into a train_parameters.json
    train_params = {
        "data_dir": data_dir,
        "block_size": block_size,
        "vocab_size": vocab_size,
        "n_embd": n_embd,
        "n_head": n_head,
        "n_layer": n_layer,
        "ff_width": ff_width,
        "train_batch_size": train_batch_size,
        "val_batch_size": val_batch_size,
        "dropout": dropout,
        "nb_epochs": nb_epochs,
        "early_stopping_patience": early_stopping_patience,
        "nb_iters": nb_iters,
        "checkpoint_interval": checkpoint_interval,
        "decay_lr": decay_lr,
        "lr_partitions_ratios": lr_partitions_ratios,
        "lr_partitions_iters": lr_partitions_iters,
        "init_lr": init_lr,
        "max_lr": max_lr,
        "min_lr": min_lr,
        "lr_warmup_iters_ratio": lr_warmup_iters_ratio,
        "lr_decay_iters_ratio": lr_decay_iters_ratio,
        "beta1": beta1,
        "beta2": beta2,
        "weight_decay": weight_decay,
        "grad_clip": grad_clip,
        "compile": compile,
        "compile_mode": compile_mode,
        "intermediate_schedules": intermediate_schedules,
        "save_only_last_checkpoint": save_only_last_checkpoint,
    }
    with open(os.path.join(output_dir, "train_parameters.json"), "w") as f: json.dump(train_params, f, indent=4)

    # load the last checkpoint if it exists, otherwise initialize the training from scratch
    try:
        last_checkpoint = torch.load(os.path.join(output_dir, "checkpoints", "last_checkpoint.pth"))
        start_epoch = last_checkpoint["epoch"]
        start_epoch_iter = last_checkpoint["epoch_iter"] + 1
        model_state_dict = last_checkpoint["model_state_dict"]
        optimizer_state_dict = last_checkpoint["optimizer_state_dict"]
        best_val_loss = last_checkpoint["best_val_loss"]
        patience_counter = last_checkpoint["patience_counter"]
        improved_this_epoch = last_checkpoint["improved_this_epoch"]
    except FileNotFoundError:
        os.makedirs(os.path.join(output_dir, "checkpoints"), exist_ok=True)
        start_epoch = 0
        start_epoch_iter = 0
        model_state_dict = None
        optimizer_state_dict = None
        best_val_loss = float("inf")
        patience_counter = 0
        improved_this_epoch = False

    # initialize the model
    model = GPT(
        intermediate_schedules=intermediate_schedules,
        vocab_size=vocab_size,
        n_embd=n_embd,
        n_head=n_head,
        n_layer=n_layer,
        dropout=dropout,
        ff_width=ff_width,
        block_size=block_size
    ).to(device)
    loguru.logger.info(f"The model has {human_readable(sum(p.numel() for p in model.parameters() if p.requires_grad))} trainable parameters")
    train_model = model
    if model_state_dict is not None:
        train_model.load_state_dict(model_state_dict)
    if compile:
        train_model = torch.compile(train_model, mode=compile_mode)

    # initialize the optimizer
    param_dict = {pn: p for pn, p in train_model.named_parameters()}
    ## filter out those that do not require grad
    param_dict = {pn: p for pn, p in param_dict.items() if p.requires_grad}
    ## create optim groups. Any parameters that is 2D will be weight decayed, otherwise no.
    ## i.e. all weight tensors in matmuls + embeddings decay, all biases and layernorms don't.
    decay_params = [p for n, p in param_dict.items() if p.dim() >= 2]
    nodecay_params = [p for n, p in param_dict.items() if p.dim() < 2]
    optim_groups = [
        {"params": decay_params, "weight_decay": weight_decay},
        {"params": nodecay_params, "weight_decay": 0.0},
    ]
    num_decay_params = sum(p.numel() for p in decay_params)
    num_nodecay_params = sum(p.numel() for p in nodecay_params)
    loguru.logger.info(f"num decayed parameter tensors: {len(decay_params)}, with {num_decay_params:,} parameters")
    loguru.logger.info(f"num non-decayed parameter tensors: {len(nodecay_params)}, with {num_nodecay_params:,} parameters")
    ## create AdamW optimizer and use the fused version if it is available
    fused_available = "fused" in inspect.signature(torch.optim.AdamW).parameters
    use_fused = fused_available and ("cuda" in device)
    loguru.logger.info(f"using fused AdamW: {use_fused}")
    extra_args = dict(fused=True) if use_fused else dict()
    optimizer = torch.optim.AdamW(optim_groups, lr=init_lr, betas=(beta1, beta2), **extra_args)
    ## load the optimizer state if it exists
    if optimizer_state_dict is not None:
        optimizer.load_state_dict(optimizer_state_dict)

    # set the torch precision to tf32
    torch.set_float32_matmul_precision("high")

    # initialize the np memmap array to save the batch losses
    batch_losses_path = os.path.join(output_dir, "batch_losses.npy")
    last_batch_loss_idx_path = os.path.join(output_dir, "last_batch_loss_idx.npy")
    val_losses_path = os.path.join(output_dir, "val_losses.npy")
    last_val_loss_idx_path = os.path.join(output_dir, "last_val_loss_idx.npy")

    try:
        batch_losses = np.lib.format.open_memmap(batch_losses_path, mode="r+", dtype=np.float32, shape=(nb_iters,))
        last_batch_loss_idx = np.lib.format.open_memmap(last_batch_loss_idx_path, mode="r+", dtype=np.int32, shape=())
        val_losses = np.lib.format.open_memmap(val_losses_path, mode="r+", dtype=np.float32, shape=(nb_epochs * math.ceil(len(train_data_loader)/checkpoint_interval),))
        last_val_loss_idx = np.lib.format.open_memmap(last_val_loss_idx_path, mode="r+", dtype=np.int32, shape=())
    except FileNotFoundError:
        batch_losses = np.lib.format.open_memmap(batch_losses_path, mode="w+", dtype=np.float32, shape=(nb_iters,))
        last_batch_loss_idx = np.lib.format.open_memmap(last_batch_loss_idx_path, mode="w+", dtype=np.int32, shape=())
        val_losses = np.lib.format.open_memmap(val_losses_path, mode="w+", dtype=np.float32, shape=(nb_epochs * math.ceil(len(train_data_loader)/checkpoint_interval),))
        last_val_loss_idx = np.lib.format.open_memmap(last_val_loss_idx_path, mode="w+", dtype=np.int32, shape=())
        last_batch_loss_idx[...] = 0
        last_batch_loss_idx.flush()
        last_val_loss_idx[...] = 0
        last_val_loss_idx.flush()

    # create data_loader for validation
    val_data_loader = torch.utils.data.DataLoader(
        FlowshopDataset(data_dir, split="val", load_in_memory=True),
        batch_size=val_batch_size,
        shuffle=False,
    )
    
    # launch the training loop
    early_stop = False
    for epoch in range(start_epoch, nb_epochs):
        if early_stop: break
        if start_epoch_iter == 0: improved_this_epoch = False

        # implement the logic to resume after failure
        ## create the generator, sampler, data loader
        generator = torch.Generator()
        generator.manual_seed(seed + epoch)
        train_sampler = torch.utils.data.RandomSampler(
            train_dataset,
            generator=generator
        )
        train_data_loader = torch.utils.data.DataLoader(
            train_dataset,
            batch_size=train_batch_size,
            sampler=train_sampler,
            drop_last=False if not compile else True,
        )
        train_data_loader_iterator = iter(train_data_loader)
        ## skip the iterations until start_iter for the epoch
        train_data_loader_iterator = itertools.islice(
            train_data_loader_iterator,
            start_epoch_iter,
            None,
        )

        # iterate over the training data loader
        for epoch_iter, (schedules_batch, makespans_batch) in (pbar:=tqdm(
            enumerate(train_data_loader_iterator, start=start_epoch_iter),
            total=len(train_data_loader),
            initial=start_epoch_iter,
            desc=f"Epoch {epoch+1}/{nb_epochs}",
        )):
            with open(os.path.join(output_dir, "train_pbar_epoch.log"), "w") as f: f.write(str(pbar))
        
            # move the batch to the device
            schedules_batch = schedules_batch.to(device)
            makespans_batch = makespans_batch.to(device)

            # clear the gradients
            optimizer.zero_grad(set_to_none=True)

            # forward pass and compute the loss
            makespans, loss = train_model(schedules_batch, makespans_batch)

            # backward pass
            loss.backward()

            # clip the gradients if grad_clip is set to a non-zero value
            if grad_clip != 0.0: torch.nn.utils.clip_grad_norm_(train_model.parameters(), grad_clip)

            # get the learning rate for the current iteration and set it in the optimizer
            current_iter = epoch * len(train_data_loader) + epoch_iter
            lr = get_lr(current_iter) if decay_lr else init_lr
            for param_group in optimizer.param_groups: param_group["lr"] = lr

            # update the parameters
            optimizer.step()

            # save the training loss for the current iteration
            batch_losses[current_iter] = loss.item()
            last_batch_loss_idx[...] = current_iter
            batch_losses.flush()
            last_batch_loss_idx.flush()

            # validation and checkpointing
            if (epoch_iter + 1) % checkpoint_interval == 0 or (epoch_iter + 1) == len(train_data_loader):

                # initialize the total validation loss
                total_val_loss = 0

                # iterate over the validation data loader
                for schedules_batch, makespans_batch in (pbar2:=tqdm(
                    val_data_loader,
                    desc=f"Validation {epoch+(epoch_iter+1)/len(train_data_loader):.2f}",
                )):
                    with open(os.path.join(output_dir, "train_pbar_val.log"), "w") as f: f.write(str(pbar2))

                    # move the batch to the device
                    schedules_batch = schedules_batch.to(device)
                    makespans_batch = makespans_batch.to(device)

                    # compute the validation loss without gradient tracking, and update the total validation loss
                    with torch.no_grad():
                        makespans, loss = train_model(schedules_batch, makespans_batch)
                    total_val_loss += loss.item() * schedules_batch.size(0)
                # ======
                with open(os.path.join(output_dir, "train_pbar_val.log"), "w") as f: f.write(str(pbar2))

                # compute the total validation loss (averaging over the dataset)
                total_val_loss /= len(val_data_loader.dataset)
                val_loss_idx = epoch * math.ceil(len(train_data_loader)/checkpoint_interval) + epoch_iter // checkpoint_interval
                val_losses[val_loss_idx] = total_val_loss
                last_val_loss_idx[...] = val_loss_idx
                val_losses.flush()
                last_val_loss_idx.flush()

                # early stopping check
                if total_val_loss < best_val_loss:
                    best_val_loss = total_val_loss
                    improved_this_epoch = True

                # save the checkpoint
                checkpoint = {
                    "epoch": epoch,
                    "epoch_iter": epoch_iter,
                    "model_state_dict": train_model.state_dict(),
                    "optimizer_state_dict": optimizer.state_dict(),
                    "validation_loss": total_val_loss,
                    "time": time.strftime("%Y_%m_%d_%H_%M_%S"),
                    "best_val_loss": best_val_loss,
                    "patience_counter": patience_counter,
                    "improved_this_epoch": improved_this_epoch,
                }
                torch.save(
                    checkpoint, 
                    os.path.join(output_dir, "checkpoints", "last_checkpoint.pth")
                )
                if not save_only_last_checkpoint:
                    torch.save(
                        checkpoint,
                        os.path.join(output_dir, "checkpoints", f"checkpoint_epoch_{epoch+(epoch_iter+1)/len(train_data_loader):.2f}.pth")
                    )
                if best_val_loss == total_val_loss:
                    torch.save(
                        checkpoint, 
                        os.path.join(output_dir, "checkpoints", "best_checkpoint.pth")
                    )
                # ======
            # ======
        # ======
        with open(os.path.join(output_dir, "train_pbar_epoch.log"), "w") as f: f.write(str(pbar))

        # set the start_epoch_iter to 0 for the next epoch
        start_epoch_iter = 0

        # check if early stopping should be triggered at the end of the epoch
        if improved_this_epoch:
            patience_counter = 0
        else:
            patience_counter += 1
            if patience_counter >= early_stopping_patience:
                loguru.logger.info(f"Early stopping triggered! Validation loss hasn't improved for {early_stopping_patience} epochs.")
                early_stop = True
    # ======

    # log the best validation loss
    loguru.logger.info(f"Best validation loss: {best_val_loss:.4f}")

    # create experiment termination flag file
    with open(os.path.join(output_dir, ".terminated_phase1"), "w") as f:
        pass
    # ======
# ======


if __name__ == "__main__":

    # parse arguments
    from argparse import ArgumentParser
    parser = ArgumentParser()
    parser.add_argument("--testing", type=bool, required=True)
    parser.add_argument("--seed", type=int, required=True)
    parser.add_argument("--data_dir", type=str, required=True)
    parser.add_argument("--n_embd", type=int, required=True)
    parser.add_argument("--n_head", type=int, required=True)
    parser.add_argument("--n_layer", type=int, required=True)
    parser.add_argument("--intermediate_schedules", type=bool, required=True)
    parser.add_argument("--dropout", type=float, required=True)
    parser.add_argument("--ff_width", type=int, required=True)
    parser.add_argument("--train_batch_size", type=int, required=True)
    parser.add_argument("--val_batch_size", type=int, required=True)
    parser.add_argument("--nb_epochs", type=int, required=True)
    parser.add_argument("--early_stopping_patience", type=int, required=True)
    parser.add_argument("--checkpoint_interval_ratio", type=float, required=True)
    parser.add_argument("--decay_lr", type=bool, required=True)
    parser.add_argument("--lr_partitions_ratios", type=lambda s: [float(item) for item in s.split(',')], help='Comma-separated list of floats that do not add up to 1 (e.g., 0.1,0.5,1)', required=True)
    parser.add_argument("--init_lr", type=float, required=True)
    parser.add_argument("--max_lr", type=float, required=True)
    parser.add_argument("--min_lr", type=float, required=True)
    parser.add_argument("--lr_warmup_iters_ratio", type=float, required=True)
    parser.add_argument("--lr_decay_iters_ratio", type=float, required=True)
    parser.add_argument("--beta1", type=float, required=True)
    parser.add_argument("--beta2", type=float, required=True)
    parser.add_argument("--weight_decay", type=float, required=True)
    parser.add_argument("--grad_clip", type=float, required=True)
    parser.add_argument("--compile", type=bool, required=True)
    parser.add_argument("--compile_mode", type=str, required=True)
    parser.add_argument("--save_only_last_checkpoint", type=bool, required=True)
    parser.add_argument("--output_dir", type=str, required=True)
    args = parser.parse_args()


    train(
        testing=args.testing,
        seed=args.seed,
        data_dir=args.data_dir,
        n_embd=args.n_embd,
        n_head=args.n_head,
        n_layer=args.n_layer,
        intermediate_schedules=args.intermediate_schedules,
        dropout=args.dropout,
        ff_width=args.ff_width,
        train_batch_size=args.train_batch_size,
        val_batch_size=args.val_batch_size,
        nb_epochs=args.nb_epochs,
        early_stopping_patience=args.early_stopping_patience,
        checkpoint_interval_ratio=args.checkpoint_interval_ratio,
        decay_lr=args.decay_lr,
        lr_partitions_ratios=args.lr_partitions_ratios,
        init_lr=args.init_lr,
        max_lr=args.max_lr,
        min_lr=args.min_lr,
        lr_warmup_iters_ratio=args.lr_warmup_iters_ratio,
        lr_decay_iters_ratio=args.lr_decay_iters_ratio,
        beta1=args.beta1,
        beta2=args.beta2,
        weight_decay=args.weight_decay,
        grad_clip=args.grad_clip,
        compile=args.compile,
        compile_mode=args.compile_mode,
        save_only_last_checkpoint=args.save_only_last_checkpoint,
        output_dir=args.output_dir,
    )