# Copyright 2019 DeepMind Technologies Limited. All Rights Reserved.
#
# Licensed under the Apache License, Version 2.0 (the "License");
# you may not use this file except in compliance with the License.
# You may obtain a copy of the License at
#
#     http://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS,
# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
# See the License for the specific language governing permissions and
# limitations under the License.
# ==============================================================================

"""Tests for optax._src.linear_algebra."""

from typing import Iterable

from absl.testing import absltest
from absl.testing import parameterized
import chex
import flax.linen as nn
import jax
import jax.numpy as jnp
import numpy as np
from optax import tree_utils
from optax._src import linear_algebra
import scipy.stats


class MLP(nn.Module):
  # Multi-layer perceptron (MLP).
  num_outputs: int
  hidden_sizes: Iterable[int]

  @nn.compact
  def __call__(self, x):
    for num_hidden in self.hidden_sizes:
      x = nn.Dense(num_hidden)(x)
      x = nn.gelu(x)
    return nn.Dense(self.num_outputs)(x)


class LinearAlgebraTest(chex.TestCase):

  def test_global_norm(self):
    flat_updates = jnp.array([2.0, 4.0, 3.0, 5.0], dtype=jnp.float32)
    nested_updates = dict(
        a=jnp.array([2.0, 4.0], dtype=jnp.float32),
        b=jnp.array([3.0, 5.0], dtype=jnp.float32),
    )
    np.testing.assert_array_equal(
        jnp.sqrt(jnp.sum(flat_updates**2)),
        linear_algebra.global_norm(nested_updates),
    )

  def test_power_iteration_cond_fun(self, dim=6):
    """Test the condition function for power iteration."""
    matrix = jax.random.normal(jax.random.PRNGKey(0), (dim, dim))
    matrix = matrix @ matrix.T
    all_eigenval, all_eigenvec = jax.numpy.linalg.eigh(matrix)
    dominant_eigenval = all_eigenval[-1]
    dominant_eigenvec = all_eigenvec[:, -1] * jnp.sign(all_eigenvec[:, -1][0])
    # loop variables for _power_iteration_cond_fun
    loop_vars = (
        dominant_eigenvec,
        dominant_eigenval * dominant_eigenvec,
        dominant_eigenval,
        10,
    )
    # when given the correct dominant eigenvector, the condition function
    # should stop and return False.
    cond_fun_result = linear_algebra._power_iteration_cond_fun(
        100, 1e-3, loop_vars
    )
    self.assertEqual(cond_fun_result, False)

  @chex.all_variants
  @parameterized.parameters(
      dict(implicit=True),
      dict(implicit=False),
  )
  def test_power_iteration(
      self, implicit, dim=6, tol=1e-3, num_iters=100
  ):
    """Test power_iteration by comparing to numpy.linalg.eigh."""

    if implicit:
      # test the function when the matrix is given in implicit form by a
      # matrix-vector product.
      def power_iteration(matrix, *, v0):
        return linear_algebra.power_iteration(
            lambda x: matrix @ x,
            v0=v0,
            error_tolerance=tol,
            num_iters=num_iters,
        )
    else:
      power_iteration = linear_algebra.power_iteration

    # test this function with/without jax.jit and on different devices
    power_iteration = self.variant(power_iteration)

    # create a random PSD matrix
    matrix = jax.random.normal(jax.random.PRNGKey(0), (dim, dim))
    matrix = matrix @ matrix.T
    v0 = jnp.ones((dim,))

    eigval_power, eigvec_power = power_iteration(matrix, v0=v0)
    all_eigenval, all_eigenvec = jax.numpy.linalg.eigh(matrix)

    self.assertAlmostEqual(eigval_power, all_eigenval[-1], delta=10 * tol)
    np.testing.assert_array_almost_equal(
        all_eigenvec[:, -1] * jnp.sign(all_eigenvec[:, -1][0]),
        eigvec_power * jnp.sign(eigvec_power[0]),
        decimal=3,
    )

  @chex.all_variants
  def test_power_iteration_pytree(
      self, dim=6, tol=1e-3, num_iters=100
  ):
    """Test power_iteration for matrix-vector products acting on pytrees."""

    def matrix_vector_product(x):
      # implements a block-diagonal matrix where each block is a scaled
      # identity matrix. The scaling factor is 2 and 1 for the first and second
      # block respectively.
      return {'a': 2 * x['a'], 'b': x['b']}

    @self.variant
    def power_iteration(*, v0):
      return linear_algebra.power_iteration(
          matrix_vector_product,
          v0=v0,
          error_tolerance=tol,
          num_iters=num_iters,
      )

    v0 = {'a': jnp.ones((dim,)), 'b': jnp.ones((dim,))}

    eigval_power, _ = power_iteration(v0=v0)

    # from the block-diagonal structure of matrix, largest eigenvalue is 2.
    self.assertAlmostEqual(eigval_power, 2., delta=10 * tol)

  @chex.all_variants
  def test_power_iteration_mlp_hessian(
      self, input_dim=16, output_dim=4, tol=1e-3
  ):
    """Test power_iteration on the Hessian of an MLP."""
    mlp = MLP(num_outputs=output_dim, hidden_sizes=[input_dim, 8, output_dim])
    key = jax.random.PRNGKey(0)
    key_params, key_input, key_output = jax.random.split(key, 3)
    # initialize the mlp
    params = mlp.init(key_params, jnp.ones(input_dim))
    x = jax.random.normal(key_input, (input_dim,))
    y = jax.random.normal(key_output, (output_dim,))

    @self.variant
    def train_obj(params_):
      z = mlp.apply(params_, x)
      return jnp.sum((z - y) ** 2)

    def hessian_vector_product(tangents_):
      return jax.jvp(jax.grad(train_obj), (params,), (tangents_,))[1]

    eigval_power, eigvec_power = linear_algebra.power_iteration(
        hessian_vector_product, v0=tree_utils.tree_ones_like(params)
    )

    params_flat, unravel = jax.flatten_util.ravel_pytree(params)
    eigvec_power_flat, _ = jax.flatten_util.ravel_pytree(eigvec_power)

    def train_obj_flat(params_flat_):
      params_ = unravel(params_flat_)
      return train_obj(params_)

    hessian = jax.hessian(train_obj_flat)(params_flat)
    all_eigenval, all_eigenvec = jax.numpy.linalg.eigh(hessian)

    self.assertAlmostEqual(all_eigenval[-1], eigval_power, delta=10 * tol)
    np.testing.assert_array_almost_equal(
        all_eigenvec[:, -1] * jnp.sign(all_eigenvec[:, -1][0]),
        eigvec_power_flat * jnp.sign(eigvec_power_flat[0]),
        decimal=3,
    )

  def test_matrix_inverse_pth_root(self):
    """Test for matrix inverse pth root."""

    def _gen_symmetrix_matrix(dim, condition_number):
      u = scipy.stats.ortho_group.rvs(dim=dim).astype(np.float64)
      v = u.T
      diag = np.diag([condition_number ** (-i / (dim - 1)) for i in range(dim)])
      return u @ diag @ v

    # Fails after it reaches a particular condition number.
    for e in range(2, 12):
      condition_number = 10**e
      ms = _gen_symmetrix_matrix(16, condition_number)
      self.assertLess(
          np.abs(np.linalg.cond(ms) - condition_number), condition_number * 0.01
      )
      error = linear_algebra.matrix_inverse_pth_root(
          ms.astype(np.float32), 4, ridge_epsilon=1e-12
      )[1]
      if e < 7:
        self.assertLess(error, 0.1)
      else:
        # No guarantee of success after e >= 7
        pass


if __name__ == '__main__':
  absltest.main()