core_rnn_cell.py

# Copyright 2015 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.
# ==============================================================================
"""Module implementing RNN Cells that used to be in core.

@@EmbeddingWrapper
@@InputProjectionWrapper
@@OutputProjectionWrapper
"""
from __future__ import absolute_import
from __future__ import division
from __future__ import print_function

import math

from tensorflow.python.framework import constant_op
from tensorflow.python.framework import dtypes
from tensorflow.python.framework import ops
from tensorflow.python.ops import array_ops
from tensorflow.python.ops import embedding_ops
from tensorflow.python.ops import init_ops
from tensorflow.python.ops import math_ops
from tensorflow.python.ops import nn_ops
from tensorflow.python.ops import rnn_cell_impl
from tensorflow.python.ops import variable_scope as vs
from tensorflow.python.platform import tf_logging as logging
from tensorflow.python.util import nest


# pylint: disable=protected-access,invalid-name
RNNCell = rnn_cell_impl.RNNCell
_WEIGHTS_VARIABLE_NAME = rnn_cell_impl._WEIGHTS_VARIABLE_NAME
_BIAS_VARIABLE_NAME = rnn_cell_impl._BIAS_VARIABLE_NAME
# pylint: enable=protected-access,invalid-name


class _Linear(object):
  """Linear map: sum_i(args[i] * W[i]), where W[i] is a variable.

  Args:
    args: a 2D Tensor or a list of 2D, batch, n, Tensors.
    output_size: int, second dimension of weight variable.
    dtype: data type for variables.
    build_bias: boolean, whether to build a bias variable.
    bias_initializer: starting value to initialize the bias
      (default is all zeros).
    kernel_initializer: starting value to initialize the weight.

  Raises:
    ValueError: if inputs_shape is wrong.
  """

  def __init__(self,
               args,
               output_size,
               build_bias,
               bias_initializer=None,
               kernel_initializer=None):
    self._build_bias = build_bias

    if args is None or (nest.is_sequence(args) and not args):
      raise ValueError("`args` must be specified")
    if not nest.is_sequence(args):
      args = [args]
      self._is_sequence = False
    else:
      self._is_sequence = True

    # Calculate the total size of arguments on dimension 1.
    total_arg_size = 0
    shapes = [a.get_shape() for a in args]
    for shape in shapes:
      if shape.ndims != 2:
        raise ValueError("linear is expecting 2D arguments: %s" % shapes)
      if shape[1].value is None:
        raise ValueError("linear expects shape[1] to be provided for shape %s, "
                         "but saw %s" % (shape, shape[1]))
      else:
        total_arg_size += shape[1].value

    dtype = [a.dtype for a in args][0]

    scope = vs.get_variable_scope()
    with vs.variable_scope(scope) as outer_scope:
      self._weights = vs.get_variable(
          _WEIGHTS_VARIABLE_NAME, [total_arg_size, output_size],
          dtype=dtype,
          initializer=kernel_initializer)
      if build_bias:
        with vs.variable_scope(outer_scope) as inner_scope:
          inner_scope.set_partitioner(None)
          if bias_initializer is None:
            bias_initializer = init_ops.constant_initializer(0.0, dtype=dtype)
          self._biases = vs.get_variable(
              _BIAS_VARIABLE_NAME, [output_size],
              dtype=dtype,
              initializer=bias_initializer)

  def __call__(self, args):
    if not self._is_sequence:
      args = [args]

    if len(args) == 1:
      res = math_ops.matmul(args[0], self._weights)
    else:
      # Explicitly creating a one for a minor performance improvement.
      one = constant_op.constant(1, dtype=dtypes.int32)
      res = math_ops.matmul(array_ops.concat(args, one), self._weights)
    if self._build_bias:
      res = nn_ops.bias_add(res, self._biases)
    return res


# TODO(xpan): Remove this function in a follow up.
def _linear(args,
            output_size,
            bias,
            bias_initializer=None,
            kernel_initializer=None):
  """Linear map: sum_i(args[i] * W[i]), where W[i] is a variable.

  Args:
    args: a 2D Tensor or a list of 2D, batch, n, Tensors.
    output_size: int, second dimension of W[i].
    bias: boolean, whether to add a bias term or not.
    bias_initializer: starting value to initialize the bias
      (default is all zeros).
    kernel_initializer: starting value to initialize the weight.

  Returns:
    A 2D Tensor with shape `[batch, output_size]` equal to
    sum_i(args[i] * W[i]), where W[i]s are newly created matrices.

  Raises:
    ValueError: if some of the arguments has unspecified or wrong shape.
  """
  if args is None or (nest.is_sequence(args) and not args):
    raise ValueError("`args` must be specified")
  if not nest.is_sequence(args):
    args = [args]

  # Calculate the total size of arguments on dimension 1.
  total_arg_size = 0
  shapes = [a.get_shape() for a in args]
  for shape in shapes:
    if shape.ndims != 2:
      raise ValueError("linear is expecting 2D arguments: %s" % shapes)
    if shape[1].value is None:
      raise ValueError("linear expects shape[1] to be provided for shape %s, "
                       "but saw %s" % (shape, shape[1]))
    else:
      total_arg_size += shape[1].value

  dtype = [a.dtype for a in args][0]

  # Now the computation.
  scope = vs.get_variable_scope()
  with vs.variable_scope(scope) as outer_scope:
    weights = vs.get_variable(
        _WEIGHTS_VARIABLE_NAME, [total_arg_size, output_size],
        dtype=dtype,
        initializer=kernel_initializer)
    if len(args) == 1:
      res = math_ops.matmul(args[0], weights)
    else:
      res = math_ops.matmul(array_ops.concat(args, 1), weights)
    if not bias:
      return res
    with vs.variable_scope(outer_scope) as inner_scope:
      inner_scope.set_partitioner(None)
      if bias_initializer is None:
        bias_initializer = init_ops.constant_initializer(0.0, dtype=dtype)
      biases = vs.get_variable(
          _BIAS_VARIABLE_NAME, [output_size],
          dtype=dtype,
          initializer=bias_initializer)
    return nn_ops.bias_add(res, biases)


class EmbeddingWrapper(RNNCell):
  """Operator adding input embedding to the given cell.

  Note: in many cases it may be more efficient to not use this wrapper,
  but instead concatenate the whole sequence of your inputs in time,
  do the embedding on this batch-concatenated sequence, then split it and
  feed into your RNN.
  """

  def __init__(self,
               cell,
               embedding_classes,
               embedding_size,
               initializer=None,
               reuse=None):
    """Create a cell with an added input embedding.

    Args:
      cell: an RNNCell, an embedding will be put before its inputs.
      embedding_classes: integer, how many symbols will be embedded.
      embedding_size: integer, the size of the vectors we embed into.
      initializer: an initializer to use when creating the embedding;
        if None, the initializer from variable scope or a default one is used.
      reuse: (optional) Python boolean describing whether to reuse variables
        in an existing scope.  If not `True`, and the existing scope already has
        the given variables, an error is raised.

    Raises:
      TypeError: if cell is not an RNNCell.
      ValueError: if embedding_classes is not positive.
    """
    super(EmbeddingWrapper, self).__init__(_reuse=reuse)
    rnn_cell_impl.assert_like_rnncell("cell", cell)
    if embedding_classes <= 0 or embedding_size <= 0:
      raise ValueError("Both embedding_classes and embedding_size must be > 0: "
                       "%d, %d." % (embedding_classes, embedding_size))
    self._cell = cell
    self._embedding_classes = embedding_classes
    self._embedding_size = embedding_size
    self._initializer = initializer

  @property
  def state_size(self):
    return self._cell.state_size

  @property
  def output_size(self):
    return self._cell.output_size

  def zero_state(self, batch_size, dtype):
    with ops.name_scope(type(self).__name__ + "ZeroState", values=[batch_size]):
      return self._cell.zero_state(batch_size, dtype)

  def call(self, inputs, state):
    """Run the cell on embedded inputs."""
    with ops.device("/cpu:0"):
      if self._initializer:
        initializer = self._initializer
      elif vs.get_variable_scope().initializer:
        initializer = vs.get_variable_scope().initializer
      else:
        # Default initializer for embeddings should have variance=1.
        sqrt3 = math.sqrt(3)  # Uniform(-sqrt(3), sqrt(3)) has variance=1.
        initializer = init_ops.random_uniform_initializer(-sqrt3, sqrt3)

      if isinstance(state, tuple):
        data_type = state[0].dtype
      else:
        data_type = state.dtype

      embedding = vs.get_variable(
          "embedding", [self._embedding_classes, self._embedding_size],
          initializer=initializer,
          dtype=data_type)
      embedded = embedding_ops.embedding_lookup(embedding,
                                                array_ops.reshape(inputs, [-1]))

      return self._cell(embedded, state)


class InputProjectionWrapper(RNNCell):
  """Operator adding an input projection to the given cell.

  Note: in many cases it may be more efficient to not use this wrapper,
  but instead concatenate the whole sequence of your inputs in time,
  do the projection on this batch-concatenated sequence, then split it.
  """

  def __init__(self,
               cell,
               num_proj,
               activation=None,
               input_size=None,
               reuse=None):
    """Create a cell with input projection.

    Args:
      cell: an RNNCell, a projection of inputs is added before it.
      num_proj: Python integer.  The dimension to project to.
      activation: (optional) an optional activation function.
      input_size: Deprecated and unused.
      reuse: (optional) Python boolean describing whether to reuse variables
        in an existing scope.  If not `True`, and the existing scope already has
        the given variables, an error is raised.

    Raises:
      TypeError: if cell is not an RNNCell.
    """
    super(InputProjectionWrapper, self).__init__(_reuse=reuse)
    if input_size is not None:
      logging.warn("%s: The input_size parameter is deprecated.", self)
    rnn_cell_impl.assert_like_rnncell("cell", cell)
    self._cell = cell
    self._num_proj = num_proj
    self._activation = activation
    self._linear = None

  @property
  def state_size(self):
    return self._cell.state_size

  @property
  def output_size(self):
    return self._cell.output_size

  def zero_state(self, batch_size, dtype):
    with ops.name_scope(type(self).__name__ + "ZeroState", values=[batch_size]):
      return self._cell.zero_state(batch_size, dtype)

  def call(self, inputs, state):
    """Run the input projection and then the cell."""
    # Default scope: "InputProjectionWrapper"
    if self._linear is None:
      self._linear = _Linear(inputs, self._num_proj, True)
    projected = self._linear(inputs)
    if self._activation:
      projected = self._activation(projected)
    return self._cell(projected, state)


class OutputProjectionWrapper(RNNCell):
  """Operator adding an output projection to the given cell.

  Note: in many cases it may be more efficient to not use this wrapper,
  but instead concatenate the whole sequence of your outputs in time,
  do the projection on this batch-concatenated sequence, then split it
  if needed or directly feed into a softmax.
  """

  def __init__(self, cell, output_size, activation=None, reuse=None):
    """Create a cell with output projection.

    Args:
      cell: an RNNCell, a projection to output_size is added to it.
      output_size: integer, the size of the output after projection.
      activation: (optional) an optional activation function.
      reuse: (optional) Python boolean describing whether to reuse variables
        in an existing scope.  If not `True`, and the existing scope already has
        the given variables, an error is raised.

    Raises:
      TypeError: if cell is not an RNNCell.
      ValueError: if output_size is not positive.
    """
    super(OutputProjectionWrapper, self).__init__(_reuse=reuse)
    rnn_cell_impl.assert_like_rnncell("cell", cell)
    if output_size < 1:
      raise ValueError("Parameter output_size must be > 0: %d." % output_size)
    self._cell = cell
    self._output_size = output_size
    self._activation = activation
    self._linear = None

  @property
  def state_size(self):
    return self._cell.state_size

  @property
  def output_size(self):
    return self._output_size

  def zero_state(self, batch_size, dtype):
    with ops.name_scope(type(self).__name__ + "ZeroState", values=[batch_size]):
      return self._cell.zero_state(batch_size, dtype)

  def call(self, inputs, state):
    """Run the cell and output projection on inputs, starting from state."""
    output, res_state = self._cell(inputs, state)
    if self._linear is None:
      self._linear = _Linear(output, self._output_size, True)
    projected = self._linear(output)
    if self._activation:
      projected = self._activation(projected)
    return projected, res_state