[TOC]

Module for constructing RNN Cells.

Abstract object representing an RNN cell.

The definition of cell in this package differs from the definition used in the literature. In the literature, cell refers to an object with a single scalar output. The definition in this package refers to a horizontal array of such units.

An RNN cell, in the most abstract setting, is anything that has a state and performs some operation that takes a matrix of inputs. This operation results in an output matrix with self.output_size columns. If self.state_size is an integer, this operation also results in a new state matrix with self.state_size columns. If self.state_size is a tuple of integers, then it results in a tuple of len(state_size) state matrices, each with a column size corresponding to values in state_size.

This module provides a number of basic commonly used RNN cells, such as LSTM (Long Short Term Memory) or GRU (Gated Recurrent Unit), and a number of operators that allow add dropouts, projections, or embeddings for inputs. Constructing multi-layer cells is supported by the class MultiRNNCell, or by calling the rnn ops several times. Every RNNCell must have the properties below and and implement __call__ with the following signature.

Run this RNN cell on inputs, starting from the given state.

• inputs: 2-D tensor with shape [batch_size x input_size].
• state: if self.state_size is an integer, this should be a 2-D Tensor with shape [batch_size x self.state_size]. Otherwise, if self.state_size is a tuple of integers, this should be a tuple with shapes [batch_size x s] for s in self.state_size.
• scope: VariableScope for the created subgraph; defaults to class name.

A pair containing:

• Output: A 2-D tensor with shape [batch_size x self.output_size].
• New state: Either a single 2-D tensor, or a tuple of tensors matching the arity and shapes of state.

Integer or TensorShape: size of outputs produced by this cell.

size(s) of state(s) used by this cell.

It can be represented by an Integer, a TensorShape or a tuple of Integers or TensorShapes.

Return zero-filled state tensor(s).

• batch_size: int, float, or unit Tensor representing the batch size.
• dtype: the data type to use for the state.

If state_size is an int or TensorShape, then the return value is a N-D tensor of shape [batch_size x state_size] filled with zeros.

If state_size is a nested list or tuple, then the return value is a nested list or tuple (of the same structure) of 2-D tensors with the shapes [batch_size x s] for each s in state_size.

The most basic RNN cell.

Most basic RNN: output = new_state = activation(W * input + U * state + B).

Return zero-filled state tensor(s).

• batch_size: int, float, or unit Tensor representing the batch size.
• dtype: the data type to use for the state.

If state_size is an int or TensorShape, then the return value is a N-D tensor of shape [batch_size x state_size] filled with zeros.

If state_size is a nested list or tuple, then the return value is a nested list or tuple (of the same structure) of 2-D tensors with the shapes [batch_size x s] for each s in state_size.

Basic LSTM recurrent network cell.

The implementation is based on: http://arxiv.org/abs/1409.2329.

We add forget_bias (default: 1) to the biases of the forget gate in order to reduce the scale of forgetting in the beginning of the training.

It does not allow cell clipping, a projection layer, and does not use peep-hole connections: it is the basic baseline.

For advanced models, please use the full LSTMCell that follows.

Long short-term memory cell (LSTM).

Initialize the basic LSTM cell.

• num_units: int, The number of units in the LSTM cell.
• forget_bias: float, The bias added to forget gates (see above).
• input_size: Deprecated and unused.
• state_is_tuple: If True, accepted and returned states are 2-tuples of the c_state and m_state. If False, they are concatenated along the column axis. The latter behavior will soon be deprecated.
• activation: Activation function of the inner states.

Return zero-filled state tensor(s).

• batch_size: int, float, or unit Tensor representing the batch size.
• dtype: the data type to use for the state.

If state_size is an int or TensorShape, then the return value is a N-D tensor of shape [batch_size x state_size] filled with zeros.

If state_size is a nested list or tuple, then the return value is a nested list or tuple (of the same structure) of 2-D tensors with the shapes [batch_size x s] for each s in state_size.

Gated Recurrent Unit cell (cf. http://arxiv.org/abs/1406.1078).

Gated recurrent unit (GRU) with nunits cells.

Return zero-filled state tensor(s).

• batch_size: int, float, or unit Tensor representing the batch size.
• dtype: the data type to use for the state.

If state_size is an int or TensorShape, then the return value is a N-D tensor of shape [batch_size x state_size] filled with zeros.

If state_size is a nested list or tuple, then the return value is a nested list or tuple (of the same structure) of 2-D tensors with the shapes [batch_size x s] for each s in state_size.

Long short-term memory unit (LSTM) recurrent network cell.

The default non-peephole implementation is based on:

http://deeplearning.cs.cmu.edu/pdfs/Hochreiter97_lstm.pdf

S. Hochreiter and J. Schmidhuber. "Long Short-Term Memory". Neural Computation, 9(8):1735-1780, 1997.

The peephole implementation is based on:

https://research.google.com/pubs/archive/43905.pdf

Hasim Sak, Andrew Senior, and Francoise Beaufays. "Long short-term memory recurrent neural network architectures for large scale acoustic modeling." INTERSPEECH, 2014.

The class uses optional peep-hole connections, optional cell clipping, and an optional projection layer.

Run one step of LSTM.

• inputs: input Tensor, 2D, batch x num_units.
• state: if state_is_tuple is False, this must be a state Tensor, 2-D, batch x state_size. If state_is_tuple is True, this must be a tuple of state Tensors, both 2-D, with column sizes c_state and m_state.
• scope: VariableScope for the created subgraph; defaults to "LSTMCell".

A tuple containing:

• A 2-D, [batch x output_dim], Tensor representing the output of the LSTM after reading inputs when previous state was state. Here output_dim is: num_proj if num_proj was set, num_units otherwise.
• Tensor(s) representing the new state of LSTM after reading inputs when the previous state was state. Same type and shape(s) as state.

• ValueError: If input size cannot be inferred from inputs via static shape inference.

Initialize the parameters for an LSTM cell.

• num_units: int, The number of units in the LSTM cell

• input_size: Deprecated and unused.

• use_peepholes: bool, set True to enable diagonal/peephole connections.

• cell_clip: (optional) A float value, if provided the cell state is clipped by this value prior to the cell output activation.

• initializer: (optional) The initializer to use for the weight and projection matrices.

• num_proj: (optional) int, The output dimensionality for the projection matrices. If None, no projection is performed.

• proj_clip: (optional) A float value. If num_proj > 0 and proj_clip is provided, then the projected values are clipped elementwise to within [-proj_clip, proj_clip].

• num_unit_shards: How to split the weight matrix. If >1, the weight matrix is stored across num_unit_shards.

• num_proj_shards: How to split the projection matrix. If >1, the projection matrix is stored across num_proj_shards.

• forget_bias: Biases of the forget gate are initialized by default to 1 in order to reduce the scale of forgetting at the beginning of the training.

• state_is_tuple: If True, accepted and returned states are 2-tuples of the c_state and m_state. If False, they are concatenated along the column axis. This latter behavior will soon be deprecated.

• activation: Activation function of the inner states.

Return zero-filled state tensor(s).

• batch_size: int, float, or unit Tensor representing the batch size.
• dtype: the data type to use for the state.

If state_size is an int or TensorShape, then the return value is a N-D tensor of shape [batch_size x state_size] filled with zeros.

If state_size is a nested list or tuple, then the return value is a nested list or tuple (of the same structure) of 2-D tensors with the shapes [batch_size x s] for each s in state_size.

Tuple used by LSTM Cells for state_size, zero_state, and output state.

Stores two elements: (c, h), in that order.

Only used when state_is_tuple=True.

Return self as a plain tuple. Used by copy and pickle.

Exclude the OrderedDict from pickling

Create new instance of LSTMStateTuple(c, h)

Return a nicely formatted representation string

Alias for field number 0

Alias for field number 1

RNN cell composed sequentially of multiple simple cells.

Run this multi-layer cell on inputs, starting from state.

Create a RNN cell composed sequentially of a number of RNNCells.

• cells: list of RNNCells that will be composed in this order.
• state_is_tuple: If True, accepted and returned states are n-tuples, where n = len(cells). If False, the states are all concatenated along the column axis. This latter behavior will soon be deprecated.

• ValueError: if cells is empty (not allowed), or at least one of the cells returns a state tuple but the flag state_is_tuple is False.

Return zero-filled state tensor(s).

• batch_size: int, float, or unit Tensor representing the batch size.
• dtype: the data type to use for the state.

If state_size is an int or TensorShape, then the return value is a N-D tensor of shape [batch_size x state_size] filled with zeros.

If state_size is a nested list or tuple, then the return value is a nested list or tuple (of the same structure) of 2-D tensors with the shapes [batch_size x s] for each s in state_size.

Operator adding dropout to inputs and outputs of the given cell.

Run the cell with the declared dropouts.

Create a cell with added input and/or output dropout.

Dropout is never used on the state.

• cell: an RNNCell, a projection to output_size is added to it.
• input_keep_prob: unit Tensor or float between 0 and 1, input keep probability; if it is float and 1, no input dropout will be added.
• output_keep_prob: unit Tensor or float between 0 and 1, output keep probability; if it is float and 1, no output dropout will be added.
• seed: (optional) integer, the randomness seed.

• TypeError: if cell is not an RNNCell.
• ValueError: if keep_prob is not between 0 and 1.

Return zero-filled state tensor(s).

• batch_size: int, float, or unit Tensor representing the batch size.
• dtype: the data type to use for the state.

If state_size is an int or TensorShape, then the return value is a N-D tensor of shape [batch_size x state_size] filled with zeros.

If state_size is a nested list or tuple, then the return value is a nested list or tuple (of the same structure) of 2-D tensors with the shapes [batch_size x s] for each s in state_size.

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.

Run the cell on embedded inputs.

Create a cell with an added input embedding.

• 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.

• TypeError: if cell is not an RNNCell.
• ValueError: if embedding_classes is not positive.

Return zero-filled state tensor(s).

• batch_size: int, float, or unit Tensor representing the batch size.
• dtype: the data type to use for the state.

If state_size is an int or TensorShape, then the return value is a N-D tensor of shape [batch_size x state_size] filled with zeros.

If state_size is a nested list or tuple, then the return value is a nested list or tuple (of the same structure) of 2-D tensors with the shapes [batch_size x s] for each s in state_size.

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.

Run the input projection and then the cell.

Create a cell with input projection.

• cell: an RNNCell, a projection of inputs is added before it.
• num_proj: Python integer. The dimension to project to.
• input_size: Deprecated and unused.

• TypeError: if cell is not an RNNCell.

Return zero-filled state tensor(s).

• batch_size: int, float, or unit Tensor representing the batch size.
• dtype: the data type to use for the state.

If state_size is an int or TensorShape, then the return value is a N-D tensor of shape [batch_size x state_size] filled with zeros.

If state_size is a nested list or tuple, then the return value is a nested list or tuple (of the same structure) of 2-D tensors with the shapes [batch_size x s] for each s in state_size.

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.

Run the cell and output projection on inputs, starting from state.

Create a cell with output projection.

• cell: an RNNCell, a projection to output_size is added to it.
• output_size: integer, the size of the output after projection.

• TypeError: if cell is not an RNNCell.
• ValueError: if output_size is not positive.

Return zero-filled state tensor(s).

• batch_size: int, float, or unit Tensor representing the batch size.
• dtype: the data type to use for the state.

If state_size is an int or TensorShape, then the return value is a N-D tensor of shape [batch_size x state_size] filled with zeros.

If state_size is a nested list or tuple, then the return value is a nested list or tuple (of the same structure) of 2-D tensors with the shapes [batch_size x s] for each s in state_size.