# Copyright 2016 The TensorFlow Authors. 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 ODE solvers."""

from __future__ import absolute_import
from __future__ import division
from __future__ import print_function

import numpy as np

from tensorflow.contrib.integrate.python.ops import odes
from tensorflow.python.framework import constant_op
from tensorflow.python.framework import dtypes
from tensorflow.python.framework import errors_impl
from tensorflow.python.framework import tensor_shape
from tensorflow.python.ops import array_ops
from tensorflow.python.ops import math_ops
from tensorflow.python.platform import test


class OdeIntTest(test.TestCase):

  def setUp(self):
    super(OdeIntTest, self).setUp()
    # simple defaults (solution is a sin-wave)
    matrix = constant_op.constant([[0, 1], [-1, 0]], dtype=dtypes.float64)
    self.func = lambda y, t: math_ops.matmul(matrix, y)
    self.y0 = np.array([[1.0], [0.0]])

  def test_odeint_exp(self):
    # Test odeint by an exponential function:
    #   dy / dt = y,  y(0) = 1.0.
    # Its analytical solution is y = exp(t).
    func = lambda y, t: y
    y0 = constant_op.constant(1.0, dtype=dtypes.float64)
    t = np.linspace(0.0, 1.0, 11)
    y_solved = odes.odeint(func, y0, t)
    self.assertIn('odeint', y_solved.name)
    self.assertEqual(y_solved.get_shape(), tensor_shape.TensorShape([11]))
    with self.test_session() as sess:
      y_solved = sess.run(y_solved)
    y_true = np.exp(t)
    self.assertAllClose(y_true, y_solved)

  def test_odeint_complex(self):
    # Test a complex, linear ODE:
    #   dy / dt = k * y,  y(0) = 1.0.
    # Its analytical solution is y = exp(k * t).
    k = 1j - 0.1
    func = lambda y, t: k * y
    t = np.linspace(0.0, 1.0, 11)
    y_solved = odes.odeint(func, 1.0 + 0.0j, t)
    with self.test_session() as sess:
      y_solved = sess.run(y_solved)
    y_true = np.exp(k * t)
    self.assertAllClose(y_true, y_solved)

  def test_odeint_riccati(self):
    # The Ricatti equation is:
    #   dy / dt = (y - t) ** 2 + 1.0,  y(0) = 0.5.
    # Its analytical solution is y = 1.0 / (2.0 - t) + t.
    func = lambda t, y: (y - t)**2 + 1.0
    t = np.linspace(0.0, 1.0, 11)
    y_solved = odes.odeint(func, np.float64(0.5), t)
    with self.test_session() as sess:
      y_solved = sess.run(y_solved)
    y_true = 1.0 / (2.0 - t) + t
    self.assertAllClose(y_true, y_solved)

  def test_odeint_2d_linear(self):
    # Solve the 2D linear differential equation:
    #   dy1 / dt = 3.0 * y1 + 4.0 * y2,
    #   dy2 / dt = -4.0 * y1 + 3.0 * y2,
    #   y1(0) = 0.0,
    #   y2(0) = 1.0.
    # Its analytical solution is
    #   y1 = sin(4.0 * t) * exp(3.0 * t),
    #   y2 = cos(4.0 * t) * exp(3.0 * t).
    matrix = constant_op.constant(
        [[3.0, 4.0], [-4.0, 3.0]], dtype=dtypes.float64)
    func = lambda y, t: math_ops.matmul(matrix, y)

    y0 = constant_op.constant([[0.0], [1.0]], dtype=dtypes.float64)
    t = np.linspace(0.0, 1.0, 11)

    y_solved = odes.odeint(func, y0, t)
    with self.test_session() as sess:
      y_solved = sess.run(y_solved)

    y_true = np.zeros((len(t), 2, 1))
    y_true[:, 0, 0] = np.sin(4.0 * t) * np.exp(3.0 * t)
    y_true[:, 1, 0] = np.cos(4.0 * t) * np.exp(3.0 * t)
    self.assertAllClose(y_true, y_solved, atol=1e-5)

  def test_odeint_higher_rank(self):
    func = lambda y, t: y
    y0 = constant_op.constant(1.0, dtype=dtypes.float64)
    t = np.linspace(0.0, 1.0, 11)
    for shape in [(), (1,), (1, 1)]:
      expected_shape = (len(t),) + shape
      y_solved = odes.odeint(func, array_ops.reshape(y0, shape), t)
      self.assertEqual(y_solved.get_shape(),
                       tensor_shape.TensorShape(expected_shape))
      with self.test_session() as sess:
        y_solved = sess.run(y_solved)
        self.assertEquals(y_solved.shape, expected_shape)

  def test_odeint_all_dtypes(self):
    func = lambda y, t: y
    t = np.linspace(0.0, 1.0, 11)
    for y0_dtype in [
        dtypes.float32, dtypes.float64, dtypes.complex64, dtypes.complex128
    ]:
      for t_dtype in [dtypes.float32, dtypes.float64]:
        y0 = math_ops.cast(1.0, y0_dtype)
        y_solved = odes.odeint(func, y0, math_ops.cast(t, t_dtype))
        with self.test_session() as sess:
          y_solved = sess.run(y_solved)
        expected = np.asarray(np.exp(t))
        self.assertAllClose(y_solved, expected, rtol=1e-5)
        self.assertEqual(dtypes.as_dtype(y_solved.dtype), y0_dtype)

  def test_odeint_required_dtypes(self):
    with self.assertRaisesRegexp(TypeError, '`y0` must have a floating point'):
      odes.odeint(self.func, math_ops.cast(self.y0, dtypes.int32), [0, 1])

    with self.assertRaisesRegexp(TypeError, '`t` must have a floating point'):
      odes.odeint(self.func, self.y0, math_ops.cast([0, 1], dtypes.int32))

  def test_odeint_runtime_errors(self):
    with self.assertRaisesRegexp(ValueError, 'cannot supply `options` without'):
      odes.odeint(self.func, self.y0, [0, 1], options={'first_step': 1.0})

    y = odes.odeint(
        self.func,
        self.y0, [0, 1],
        method='dopri5',
        options={'max_num_steps': 0})
    with self.test_session() as sess:
      with self.assertRaisesRegexp(errors_impl.InvalidArgumentError,
                                   'max_num_steps'):
        sess.run(y)

    y = odes.odeint(self.func, self.y0, [1, 0])
    with self.test_session() as sess:
      with self.assertRaisesRegexp(errors_impl.InvalidArgumentError,
                                   'monotonic increasing'):
        sess.run(y)

  def test_odeint_different_times(self):
    # integrate steps should be independent of interpolation times
    times0 = np.linspace(0, 10, num=11, dtype=float)
    times1 = np.linspace(0, 10, num=101, dtype=float)

    with self.test_session() as sess:
      y_solved_0, info_0 = sess.run(
          odes.odeint(self.func, self.y0, times0, full_output=True))
      y_solved_1, info_1 = sess.run(
          odes.odeint(self.func, self.y0, times1, full_output=True))

    self.assertAllClose(y_solved_0, y_solved_1[::10])
    self.assertEqual(info_0['num_func_evals'], info_1['num_func_evals'])
    self.assertAllEqual(info_0['integrate_points'], info_1['integrate_points'])
    self.assertAllEqual(info_0['error_ratio'], info_1['error_ratio'])

  def test_odeint_5th_order_accuracy(self):
    t = [0, 20]
    kwargs = dict(
        full_output=True, method='dopri5', options=dict(max_num_steps=2000))
    with self.test_session() as sess:
      _, info_0 = sess.run(
          odes.odeint(self.func, self.y0, t, rtol=0, atol=1e-6, **kwargs))
      _, info_1 = sess.run(
          odes.odeint(self.func, self.y0, t, rtol=0, atol=1e-9, **kwargs))
    self.assertAllClose(
        info_0['integrate_points'].size * 1000**0.2,
        float(info_1['integrate_points'].size),
        rtol=0.01)


class StepSizeTest(test.TestCase):

  def test_error_ratio_one(self):
    new_step = odes._optimal_step_size(
        last_step=constant_op.constant(1.0),
        error_ratio=constant_op.constant(1.0))
    with self.test_session() as sess:
      new_step = sess.run(new_step)
    self.assertAllClose(new_step, 0.9)

  def test_ifactor(self):
    new_step = odes._optimal_step_size(
        last_step=constant_op.constant(1.0),
        error_ratio=constant_op.constant(0.0))
    with self.test_session() as sess:
      new_step = sess.run(new_step)
    self.assertAllClose(new_step, 10.0)

  def test_dfactor(self):
    new_step = odes._optimal_step_size(
        last_step=constant_op.constant(1.0),
        error_ratio=constant_op.constant(1e6))
    with self.test_session() as sess:
      new_step = sess.run(new_step)
    self.assertAllClose(new_step, 0.2)


class InterpolationTest(test.TestCase):

  def test_5th_order_polynomial(self):
    # this should be an exact fit
    f = lambda x: x**4 + x**3 - 2 * x**2 + 4 * x + 5
    f_prime = lambda x: 4 * x**3 + 3 * x**2 - 4 * x + 4
    coeffs = odes._interp_fit(
        f(0.0), f(10.0), f(5.0), f_prime(0.0), f_prime(10.0), 10.0)
    times = np.linspace(0, 10, dtype=np.float32)
    y_fit = array_ops.stack(
        [odes._interp_evaluate(coeffs, 0.0, 10.0, t) for t in times])
    y_expected = f(times)
    with self.test_session() as sess:
      y_actual = sess.run(y_fit)
      self.assertAllClose(y_expected, y_actual)

    # attempt interpolation outside bounds
    y_invalid = odes._interp_evaluate(coeffs, 0.0, 10.0, 100.0)
    with self.test_session() as sess:
      with self.assertRaises(errors_impl.InvalidArgumentError):
        sess.run(y_invalid)


class OdeIntFixedTest(test.TestCase):

  def _test_integrate_sine(self, method):

    def evol_func(y, t):
      del t
      return array_ops.stack([y[1], -y[0]])

    y0 = [0., 1.]
    time_grid = np.linspace(0., 10., 200)
    y_grid = odes.odeint_fixed(evol_func, y0, time_grid, method=method)

    with self.test_session() as sess:
      y_grid_array = sess.run(y_grid)

    np.testing.assert_allclose(
        y_grid_array[:, 0], np.sin(time_grid), rtol=1e-2, atol=1e-2)

  def _test_integrate_gaussian(self, method):

    def evol_func(y, t):
      return -math_ops.cast(t, dtype=y.dtype) * y[0]

    y0 = [1.]
    time_grid = np.linspace(0., 2., 100)
    y_grid = odes.odeint_fixed(evol_func, y0, time_grid, method=method)

    with self.test_session() as sess:
      y_grid_array = sess.run(y_grid)

    np.testing.assert_allclose(
        y_grid_array[:, 0], np.exp(-time_grid**2 / 2), rtol=1e-2, atol=1e-2)

  def _test_everything(self, method):
    self._test_integrate_sine(method)
    self._test_integrate_gaussian(method)

  def test_midpoint(self):
    self._test_everything('midpoint')

  def test_rk4(self):
    self._test_everything('rk4')


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