text: # Copyright 2019 Google LLC
  #
  # 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
  #
  #     https://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.
  """PDE solver methods."""
  
  from __future__ import absolute_import
  from __future__ import division
  from __future__ import print_function
  
  from tf_quant_finance.math.pde import grids
  from tf_quant_finance.math.pde import time_marching_schemes
  from tf_quant_finance.math.pde.grid_stepper import BackwardGridStepper
  from tf_quant_finance.math.pde.grid_stepper import GridStepperState
  from tf_quant_finance.math.pde.pde_kernels import ParabolicDifferentialEquationSolver
  
  from tensorflow.python.util.all_util import remove_undocumented  # pylint: disable=g-direct-tensorflow-import
  
  _allowed_symbols = [
      'BackwardGridStepper',
      'GridStepperState',
      'grids',
      'ParabolicDifferentialEquationSolver',
      'time_marching_schemes',
  ]
  
  remove_undocumented(__name__, _allowed_symbols)
  