text: # Copyright 2018 The TensorFlow Probability Authors.
  #
  # 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.
  # ============================================================================
  """Numpy implementations of sparse functions."""
  
  from __future__ import absolute_import
  from __future__ import division
  from __future__ import print_function
  
  import tensorflow as tf
  
  from tensorflow_probability.python.internal.backend.numpy import _utils as utils
  
  
  __all__ = [
      'to_dense',
  ]
  
  
  def _to_dense(sp_input, default_value=0, validate_indices=True, name=None):  # pylint: disable=unused-argument
    if default_value != 0:
      raise NotImplementedError(
          'Argument `default_value != 0` is currently unimplemented.')
    if not validate_indices:
      raise NotImplementedError(
          'Argument `validate_indices != True` is currently unimplemented.')
    return sp_input
  
  
  # --- Begin Public Functions --------------------------------------------------
  
  
  # TODO(b/136555907): Add unit test.
  to_dense = utils.copy_docstring(
      tf.sparse.to_dense,
      _to_dense)
  