# -*- coding: utf-8 -*- #
"""*********************************************************************************************"""
# FileName [ tf_seq2seq_model.py ]
# Synopsis [ Tensorflow modules for generator ]
# Author [ Ting-Wei Liu (Andi611) ]
# Copyright [ Copyleft(c), NTUEE, NTU, Taiwan ]
"""*********************************************************************************************"""
import numpy as np
import tensorflow as tf
from tensorflow.python import shape
from tensorflow.python.framework import dtypes
from tensorflow.python.framework import ops
from tensorflow.python.ops import array_ops
from tensorflow.python.ops import control_flow_ops
from tensorflow.python.ops import embedding_ops
from tensorflow.python.ops import math_ops
from tensorflow.python.ops import nn_ops
from tensorflow.python.ops import rnn
from tensorflow.python.ops import rnn_cell
from tensorflow.python.ops import variable_scope
from tensorflow.python.util import nest
def linear(args, output_size, bias, bias_start=0.1, scope=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 x n, Tensors.
output_size: int, second dimension of W[i].
bias: boolean, whether to add a bias term or not.
bias_start: starting value to initialize the bias; 0 by default.
scope: (optional) Variable scope to create parameters in.
Returns:
A 2D Tensor with shape [batch x 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 %d" % (shape, shape[1]))
else:
total_arg_size += shape[1].value
dtype = [a.dtype for a in args][0]
# Now the computation.
scope = tf.get_variable_scope()
with tf.variable_scope(scope) as outer_scope:
weights = tf.get_variable(
"weights", [total_arg_size, output_size], dtype=dtype)
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 tf.variable_scope(outer_scope) as inner_scope:
inner_scope.set_partitioner(None)
biases = tf.get_variable(
"biases", [output_size],
dtype=dtype,
initializer=tf.constant_initializer(bias_start, dtype=dtype))
return nn_ops.bias_add(res, biases)
def _argmax_or_mcsearch(embedding, output_projection=None, update_embedding=True, mc_search=False):
def loop_function(prev, _):
if output_projection is not None:
prev = nn_ops.xw_plus_b(prev, output_projection[0], output_projection[1])
if isinstance(mc_search, bool):
prev_symbol = tf.reshape(tf.multinomial(prev, 1), [-1]) if mc_search else math_ops.argmax(prev, 1)
else:
prev_symbol = tf.cond(mc_search, lambda: tf.reshape(tf.multinomial(prev, 1), [-1]), lambda: tf.argmax(prev, 1))
emb_prev = embedding_ops.embedding_lookup(embedding, prev_symbol)
if not update_embedding:
emb_prev = array_ops.stop_gradient(emb_prev)
return emb_prev
return loop_function
def _extract_argmax_and_embed(embedding, output_projection=None, update_embedding=True):
"""Get a loop_function that extracts the previous symbol and embeds it.
Args:
embedding: embedding tensor for symbols.
output_projection: None or a pair (W, B). If provided, each fed previous
output will first be multiplied by W and added B.
update_embedding: Boolean; if False, the gradients will not propagate
through the embeddings.
Returns:
A loop function.
"""
def loop_function(prev, _):
if output_projection is not None:
prev = nn_ops.xw_plus_b(
prev, output_projection[0], output_projection[1])
prev_symbol = math_ops.argmax(prev, 1)
# Note that gradients will not propagate through the second parameter of
# embedding_lookup.
emb_prev = embedding_ops.embedding_lookup(embedding, prev_symbol)
if not update_embedding:
emb_prev = array_ops.stop_gradient(emb_prev)
return emb_prev
return loop_function
def rnn_decoder(decoder_inputs, initial_state, cell, loop_function=None,
scope=None):
"""RNN decoder for the sequence-to-sequence model.
Args:
decoder_inputs: A list of 2D Tensors [batch_size x input_size].
initial_state: 2D Tensor with shape [batch_size x cell.state_size].
cell: rnn_cell.RNNCell defining the cell function and size.
loop_function: If not None, this function will be applied to the i-th output
in order to generate the i+1-st input, and decoder_inputs will be ignored,
except for the first element ("GO" symbol). This can be used for decoding,
but also for training to emulate http://arxiv.org/abs/1506.03099.
Signature -- loop_function(prev, i) = next
* prev is a 2D Tensor of shape [batch_size x output_size],
* i is an integer, the step number (when advanced control is needed),
* next is a 2D Tensor of shape [batch_size x input_size].
scope: VariableScope for the created subgraph; defaults to "rnn_decoder".
Returns:
A tuple of the form (outputs, state), where:
outputs: A list of the same length as decoder_inputs of 2D Tensors with
shape [batch_size x output_size] containing generated outputs.
state: The state of each cell at the final time-step.
It is a 2D Tensor of shape [batch_size x cell.state_size].
(Note that in some cases, like basic RNN cell or GRU cell, outputs and
states can be the same. They are different for LSTM cells though.)
"""
with variable_scope.variable_scope(scope or "rnn_decoder"):
state = initial_state
outputs = []
prev = None
for i, inp in enumerate(decoder_inputs):
if loop_function is not None and prev is not None:
with variable_scope.variable_scope("loop_function", reuse=True):
inp = loop_function(prev, i)
if i > 0:
variable_scope.get_variable_scope().reuse_variables()
output, state = cell(inp, state)
outputs.append(output)
if loop_function is not None:
prev = output
return outputs, state
def basic_rnn_seq2seq(
encoder_inputs, decoder_inputs, cell, dtype=dtypes.float32, scope=None):
"""Basic RNN sequence-to-sequence model.
This model first runs an RNN to encode encoder_inputs into a state vector,
then runs decoder, initialized with the last encoder state, on decoder_inputs.
Encoder and decoder use the same RNN cell type, but don't share parameters.
Args:
encoder_inputs: A list of 2D Tensors [batch_size x input_size].
decoder_inputs: A list of 2D Tensors [batch_size x input_size].
cell: rnn_cell.RNNCell defining the cell function and size.
dtype: The dtype of the initial state of the RNN cell (default: tf.float32).
scope: VariableScope for the created subgraph; default: "basic_rnn_seq2seq".
Returns:
A tuple of the form (outputs, state), where:
outputs: A list of the same length as decoder_inputs of 2D Tensors with
shape [batch_size x output_size] containing the generated outputs.
state: The state of each decoder cell in the final time-step.
It is a 2D Tensor of shape [batch_size x cell.state_size].
"""
with variable_scope.variable_scope(scope or "basic_rnn_seq2seq"):
_, enc_state = rnn.rnn(cell, encoder_inputs, dtype=dtype)
return rnn_decoder(decoder_inputs, enc_state, cell)
def tied_rnn_seq2seq(encoder_inputs, decoder_inputs, cell,
loop_function=None, dtype=dtypes.float32, scope=None):
"""RNN sequence-to-sequence model with tied encoder and decoder parameters.
This model first runs an RNN to encode encoder_inputs into a state vector, and
then runs decoder, initialized with the last encoder state, on decoder_inputs.
Encoder and decoder use the same RNN cell and share parameters.
Args:
encoder_inputs: A list of 2D Tensors [batch_size x input_size].
decoder_inputs: A list of 2D Tensors [batch_size x input_size].
cell: rnn_cell.RNNCell defining the cell function and size.
loop_function: If not None, this function will be applied to i-th output
in order to generate i+1-th input, and decoder_inputs will be ignored,
except for the first element ("GO" symbol), see rnn_decoder for details.
dtype: The dtype of the initial state of the rnn cell (default: tf.float32).
scope: VariableScope for the created subgraph; default: "tied_rnn_seq2seq".
Returns:
A tuple of the form (outputs, state), where:
outputs: A list of the same length as decoder_inputs of 2D Tensors with
shape [batch_size x output_size] containing the generated outputs.
state: The state of each decoder cell in each time-step. This is a list
with length len(decoder_inputs) -- one item for each time-step.
It is a 2D Tensor of shape [batch_size x cell.state_size].
"""
with variable_scope.variable_scope("combined_tied_rnn_seq2seq"):
scope = scope or "tied_rnn_seq2seq"
_, enc_state = rnn.rnn(
cell, encoder_inputs, dtype=dtype, scope=scope)
variable_scope.get_variable_scope().reuse_variables()
return rnn_decoder(decoder_inputs, enc_state, cell,
loop_function=loop_function, scope=scope)
def embedding_rnn_decoder(decoder_inputs,
initial_state,
cell,
num_symbols,
embedding_size,
output_projection=None,
feed_previous=False,
update_embedding_for_previous=True,
scope=None):
with variable_scope.variable_scope(scope or "embedding_rnn_decoder") as scope:
if output_projection is not None:
dtype = scope.dtype
proj_weights = ops.convert_to_tensor(output_projection[0], dtype=dtype)
proj_weights.get_shape().assert_is_compatible_with([None, num_symbols])
proj_biases = ops.convert_to_tensor(output_projection[1], dtype=dtype)
proj_biases.get_shape().assert_is_compatible_with([num_symbols])
embedding = variable_scope.get_variable("embedding",
[num_symbols, embedding_size])
loop_function = _extract_argmax_and_embed(
embedding, output_projection,
update_embedding_for_previous) if feed_previous else None
emb_inp = (
embedding_ops.embedding_lookup(embedding, i) for i in decoder_inputs)
return rnn_decoder(emb_inp, initial_state, cell,
loop_function=loop_function)
def embedding_rnn_seq2seq(encoder_inputs,
decoder_inputs,
cell,
num_encoder_symbols,
num_decoder_symbols,
embedding_size,
output_projection=None,
feed_previous=False,
dtype=None,
scope=None):
with variable_scope.variable_scope(scope or "embedding_rnn_seq2seq") as scope:
if dtype is not None:
scope.set_dtype(dtype)
else:
dtype = scope.dtype
# Encoder.
encoder_cell = rnn_cell.EmbeddingWrapper(
cell, embedding_classes=num_encoder_symbols,
embedding_size=embedding_size)
_, encoder_state = rnn.rnn(encoder_cell, encoder_inputs, dtype=dtype)
# Decoder.
if output_projection is None:
cell = rnn_cell.OutputProjectionWrapper(cell, num_decoder_symbols)
if isinstance(feed_previous, bool):
return embedding_rnn_decoder(
decoder_inputs,
encoder_state,
cell,
num_decoder_symbols,
embedding_size,
output_projection=output_projection,
feed_previous=feed_previous,
scope=scope)
# If feed_previous is a Tensor, we construct 2 graphs and use cond.
def decoder(feed_previous_bool):
reuse = None if feed_previous_bool else True
with variable_scope.variable_scope(
variable_scope.get_variable_scope(), reuse=reuse) as scope:
outputs, state = embedding_rnn_decoder(
decoder_inputs, encoder_state, cell, num_decoder_symbols,
embedding_size, output_projection=output_projection,
feed_previous=feed_previous_bool,
update_embedding_for_previous=False)
state_list = [state]
if nest.is_sequence(state):
state_list = nest.flatten(state)
return outputs + state_list
outputs_and_state = control_flow_ops.cond(feed_previous,
lambda: decoder(True),
lambda: decoder(False))
outputs_len = len(decoder_inputs) # Outputs length same as decoder inputs.
state_list = outputs_and_state[outputs_len:]
state = state_list[0]
if nest.is_sequence(encoder_state):
state = nest.pack_sequence_as(structure=encoder_state,
flat_sequence=state_list)
return outputs_and_state[:outputs_len], state
def embedding_tied_rnn_seq2seq(encoder_inputs,
decoder_inputs,
cell,
num_symbols,
embedding_size,
num_decoder_symbols=None,
output_projection=None,
feed_previous=False,
dtype=None,
scope=None):
"""Embedding RNN sequence-to-sequence model with tied (shared) parameters.
This model first embeds encoder_inputs by a newly created embedding (of shape
[num_symbols x input_size]). Then it runs an RNN to encode embedded
encoder_inputs into a state vector. Next, it embeds decoder_inputs using
the same embedding. Then it runs RNN decoder, initialized with the last
encoder state, on embedded decoder_inputs. The decoder output is over symbols
from 0 to num_decoder_symbols - 1 if num_decoder_symbols is none; otherwise it
is over 0 to num_symbols - 1.
Args:
encoder_inputs: A list of 1D int32 Tensors of shape [batch_size].
decoder_inputs: A list of 1D int32 Tensors of shape [batch_size].
cell: rnn_cell.RNNCell defining the cell function and size.
num_symbols: Integer; number of symbols for both encoder and decoder.
embedding_size: Integer, the length of the embedding vector for each symbol.
num_decoder_symbols: Integer; number of output symbols for decoder. If
provided, the decoder output is over symbols 0 to num_decoder_symbols - 1.
Otherwise, decoder output is over symbols 0 to num_symbols - 1. Note that
this assumes that the vocabulary is set up such that the first
num_decoder_symbols of num_symbols are part of decoding.
output_projection: None or a pair (W, B) of output projection weights and
biases; W has shape [output_size x num_symbols] and B has
shape [num_symbols]; if provided and feed_previous=True, each
fed previous output will first be multiplied by W and added B.
feed_previous: Boolean or scalar Boolean Tensor; if True, only the first
of decoder_inputs will be used (the "GO" symbol), and all other decoder
inputs will be taken from previous outputs (as in embedding_rnn_decoder).
If False, decoder_inputs are used as given (the standard decoder case).
dtype: The dtype to use for the initial RNN states (default: tf.float32).
scope: VariableScope for the created subgraph; defaults to
"embedding_tied_rnn_seq2seq".
Returns:
A tuple of the form (outputs, state), where:
outputs: A list of the same length as decoder_inputs of 2D Tensors with
shape [batch_size x output_symbols] containing the generated
outputs where output_symbols = num_decoder_symbols if
num_decoder_symbols is not None otherwise output_symbols = num_symbols.
state: The state of each decoder cell at the final time-step.
It is a 2D Tensor of shape [batch_size x cell.state_size].
Raises:
ValueError: When output_projection has the wrong shape.
"""
with variable_scope.variable_scope(
scope or "embedding_tied_rnn_seq2seq", dtype=dtype) as scope:
dtype = scope.dtype
if output_projection is not None:
proj_weights = ops.convert_to_tensor(output_projection[0], dtype=dtype)
proj_weights.get_shape().assert_is_compatible_with([None, num_symbols])
proj_biases = ops.convert_to_tensor(output_projection[1], dtype=dtype)
proj_biases.get_shape().assert_is_compatible_with([num_symbols])
embedding = variable_scope.get_variable(
"embedding", [num_symbols, embedding_size], dtype=dtype)
emb_encoder_inputs = [embedding_ops.embedding_lookup(embedding, x)
for x in encoder_inputs]
emb_decoder_inputs = [embedding_ops.embedding_lookup(embedding, x)
for x in decoder_inputs]
output_symbols = num_symbols
if num_decoder_symbols is not None:
output_symbols = num_decoder_symbols
if output_projection is None:
cell = rnn_cell.OutputProjectionWrapper(cell, output_symbols)
if isinstance(feed_previous, bool):
loop_function = _extract_argmax_and_embed(
embedding, output_projection, True) if feed_previous else None
return tied_rnn_seq2seq(emb_encoder_inputs, emb_decoder_inputs, cell,
loop_function=loop_function, dtype=dtype)
# If feed_previous is a Tensor, we construct 2 graphs and use cond.
def decoder(feed_previous_bool):
loop_function = _extract_argmax_and_embed(
embedding, output_projection, False) if feed_previous_bool else None
reuse = None if feed_previous_bool else True
with variable_scope.variable_scope(variable_scope.get_variable_scope(),
reuse=reuse):
outputs, state = tied_rnn_seq2seq(
emb_encoder_inputs, emb_decoder_inputs, cell,
loop_function=loop_function, dtype=dtype)
state_list = [state]
if nest.is_sequence(state):
state_list = nest.flatten(state)
return outputs + state_list
outputs_and_state = control_flow_ops.cond(feed_previous,
lambda: decoder(True),
lambda: decoder(False))
outputs_len = len(decoder_inputs) # Outputs length same as decoder inputs.
state_list = outputs_and_state[outputs_len:]
state = state_list[0]
# Calculate zero-state to know it's structure.
static_batch_size = encoder_inputs[0].get_shape()[0]
for inp in encoder_inputs[1:]:
static_batch_size.merge_with(inp.get_shape()[0])
batch_size = static_batch_size.value
if batch_size is None:
batch_size = array_ops.shape(encoder_inputs[0])[0]
zero_state = cell.zero_state(batch_size, dtype)
if nest.is_sequence(zero_state):
state = nest.pack_sequence_as(structure=zero_state,
flat_sequence=state_list)
return outputs_and_state[:outputs_len], state
def attention_decoder(decoder_inputs,
initial_state,
attention_states,
cell,
output_size=None,
num_heads=1,
loop_function=None,
dtype=None,
scope=None,
initial_state_attention=False):
"""RNN decoder with attention for the sequence-to-sequence model.
In this context "attention" means that, during decoding, the RNN can look up
information in the additional tensor attention_states, and it does this by
focusing on a few entries from the tensor. This model has proven to yield
especially good results in a number of sequence-to-sequence tasks. This
implementation is based on http://arxiv.org/abs/1412.7449 (see below for
details). It is recommended for complex sequence-to-sequence tasks.
Args:
decoder_inputs: A list of 2D Tensors [batch_size x input_size].
initial_state: 2D Tensor [batch_size x cell.state_size].
attention_states: 3D Tensor [batch_size x attn_length x attn_size].
cell: rnn_cell.RNNCell defining the cell function and size.
output_size: Size of the output vectors; if None, we use cell.output_size.
num_heads: Number of attention heads that read from attention_states.
loop_function: If not None, this function will be applied to i-th output
in order to generate i+1-th input, and decoder_inputs will be ignored,
except for the first element ("GO" symbol). This can be used for decoding,
but also for training to emulate http://arxiv.org/abs/1506.03099.
Signature -- loop_function(prev, i) = next
* prev is a 2D Tensor of shape [batch_size x output_size],
* i is an integer, the step number (when advanced control is needed),
* next is a 2D Tensor of shape [batch_size x input_size].
dtype: The dtype to use for the RNN initial state (default: tf.float32).
scope: VariableScope for the created subgraph; default: "attention_decoder".
initial_state_attention: If False (default), initial attentions are zero.
If True, initialize the attentions from the initial state and attention
states -- useful when we wish to resume decoding from a previously
stored decoder state and attention states.
Returns:
A tuple of the form (outputs, state), where:
outputs: A list of the same length as decoder_inputs of 2D Tensors of
shape [batch_size x output_size]. These represent the generated outputs.
Output i is computed from input i (which is either the i-th element
of decoder_inputs or loop_function(output {i-1}, i)) as follows.
First, we run the cell on a combination of the input and previous
attention masks:
cell_output, new_state = cell(linear(input, prev_attn), prev_state).
Then, we calculate new attention masks:
new_attn = softmax(V^T * tanh(W * attention_states + U * new_state))
and then we calculate the output:
output = linear(cell_output, new_attn).
state: The state of each decoder cell the final time-step.
It is a 2D Tensor of shape [batch_size x cell.state_size].
Raises:
ValueError: when num_heads is not positive, there are no inputs, shapes
of attention_states are not set, or input size cannot be inferred
from the input.
"""
if not decoder_inputs:
raise ValueError("Must provide at least 1 input to attention decoder.")
if num_heads < 1:
raise ValueError("With less than 1 heads, use a non-attention decoder.")
if attention_states.get_shape()[2].value is None:
raise ValueError("Shape[2] of attention_states must be known: %s"
% attention_states.get_shape())
if output_size is None:
output_size = cell.output_size
with variable_scope.variable_scope(
scope or "attention_decoder", dtype=dtype) as scope:
dtype = scope.dtype
batch_size = array_ops.shape(decoder_inputs[0])[0] # Needed for reshaping.
attn_length = attention_states.get_shape()[1].value
if attn_length is None:
attn_length = shape(attention_states)[1]
attn_size = attention_states.get_shape()[2].value
# To calculate W1 * h_t we use a 1-by-1 convolution, need to reshape before.
hidden = array_ops.reshape(
attention_states, [-1, attn_length, 1, attn_size])
hidden_features = []
v = []
attention_vec_size = attn_size # Size of query vectors for attention.
for a in range(num_heads):
k = variable_scope.get_variable("AttnW_%d" % a,
[1, 1, attn_size, attention_vec_size])
hidden_features.append(nn_ops.conv2d(hidden, k, [1, 1, 1, 1], "SAME"))
v.append(
variable_scope.get_variable("AttnV_%d" % a, [attention_vec_size]))
state = initial_state
def attention(query):
"""Put attention masks on hidden using hidden_features and query."""
ds = [] # Results of attention reads will be stored here.
if nest.is_sequence(query): # If the query is a tuple, flatten it.
query_list = nest.flatten(query)
for q in query_list: # Check that ndims == 2 if specified.
ndims = q.get_shape().ndims
if ndims:
assert ndims == 2
query = array_ops.concat(query_list, 1)
for a in range(num_heads):
with variable_scope.variable_scope("Attention_%d" % a):
y = linear(query, attention_vec_size, True)
y = array_ops.reshape(y, [-1, 1, 1, attention_vec_size])
# Attention mask is a softmax of v^T * tanh(...).
s = math_ops.reduce_sum(
v[a] * math_ops.tanh(hidden_features[a] + y), [2, 3])
a = nn_ops.softmax(s)
# Now calculate the attention-weighted vector d.
d = math_ops.reduce_sum(
array_ops.reshape(a, [-1, attn_length, 1, 1]) * hidden,
[1, 2])
ds.append(array_ops.reshape(d, [-1, attn_size]))
return ds
outputs = []
prev = None
batch_attn_size = array_ops.stack([batch_size, attn_size])
attns = [array_ops.zeros(batch_attn_size, dtype=dtype)
for _ in range(num_heads)]
for a in attns: # Ensure the second shape of attention vectors is set.
a.set_shape([None, attn_size])
if initial_state_attention:
attns = attention(initial_state)
for i, inp in enumerate(decoder_inputs):
if i > 0:
variable_scope.get_variable_scope().reuse_variables()
# If loop_function is set, we use it instead of decoder_inputs.
if loop_function is not None and prev is not None:
with variable_scope.variable_scope("loop_function", reuse=True):
inp = loop_function(prev, i)
# Merge input and previous attentions into one vector of the right size.
input_size = inp.get_shape().with_rank(2)[1]
if input_size.value is None:
raise ValueError("Could not infer input size from input: %s" % inp.name)
x = linear([inp] + attns, input_size, True)
# Run the RNN.
cell_output, state = cell(x, state)
# Run the attention mechanism.
if i == 0 and initial_state_attention:
with variable_scope.variable_scope(variable_scope.get_variable_scope(),
reuse=True):
attns = attention(state)
else:
attns = attention(state)
with variable_scope.variable_scope("AttnOutputProjection"):
output = linear([cell_output] + attns, output_size, True)
if loop_function is not None:
prev = output
outputs.append(output)
return outputs, state
def embedding_attention_decoder(decoder_inputs,
initial_state,
attention_states,
cell,
num_symbols,
embedding_size,
num_heads=1,
output_size=None,
output_projection=None,
feed_previous=False,
update_embedding_for_previous=True,
dtype=None,
scope=None,
initial_state_attention=False,
mc_search = False):
"""RNN decoder with embedding and attention and a pure-decoding option.
Args:
decoder_inputs: A list of 1D batch-sized int32 Tensors (decoder inputs).
initial_state: 2D Tensor [batch_size x cell.state_size].
attention_states: 3D Tensor [batch_size x attn_length x attn_size].
cell: rnn_cell.RNNCell defining the cell function.
num_symbols: Integer, how many symbols come into the embedding.
embedding_size: Integer, the length of the embedding vector for each symbol.
num_heads: Number of attention heads that read from attention_states.
output_size: Size of the output vectors; if None, use output_size.
output_projection: None or a pair (W, B) of output projection weights and
biases; W has shape [output_size x num_symbols] and B has shape
[num_symbols]; if provided and feed_previous=True, each fed previous
output will first be multiplied by W and added B.
feed_previous: Boolean; if True, only the first of decoder_inputs will be
used (the "GO" symbol), and all other decoder inputs will be generated by:
next = embedding_lookup(embedding, argmax(previous_output)),
In effect, this implements a greedy decoder. It can also be used
during training to emulate http://arxiv.org/abs/1506.03099.
If False, decoder_inputs are used as given (the standard decoder case).
update_embedding_for_previous: Boolean; if False and feed_previous=True,
only the embedding for the first symbol of decoder_inputs (the "GO"
symbol) will be updated by back propagation. Embeddings for the symbols
generated from the decoder itself remain unchanged. This parameter has
no effect if feed_previous=False.
dtype: The dtype to use for the RNN initial states (default: tf.float32).
scope: VariableScope for the created subgraph; defaults to
"embedding_attention_decoder".
initial_state_attention: If False (default), initial attentions are zero.
If True, initialize the attentions from the initial state and attention
states -- useful when we wish to resume decoding from a previously
stored decoder state and attention states.
Returns:
A tuple of the form (outputs, state), where:
outputs: A list of the same length as decoder_inputs of 2D Tensors with
shape [batch_size x output_size] containing the generated outputs.
state: The state of each decoder cell at the final time-step.
It is a 2D Tensor of shape [batch_size x cell.state_size].
Raises:
ValueError: When output_projection has the wrong shape.
"""
if output_size is None:
output_size = cell.output_size
if output_projection is not None:
proj_biases = ops.convert_to_tensor(output_projection[1], dtype=dtype)
proj_biases.get_shape().assert_is_compatible_with([num_symbols])
with variable_scope.variable_scope(
scope or "embedding_attention_decoder", dtype=dtype) as scope:
embedding = variable_scope.get_variable("embedding",
[num_symbols, embedding_size])
loop_function = None
if feed_previous == True:
loop_function = _argmax_or_mcsearch(embedding, output_projection, update_embedding_for_previous, mc_search)
# if isinstance(mc_search, bool):
# if feed_previous == True and mc_search == True:
# loop_function = _mc_argmax_and_embed(embedding, output_projection, update_embedding_for_previous)
# elif feed_previous == True and mc_search == False:
# loop_function = _extract_argmax_and_embed(embedding, output_projection, update_embedding_for_previous)
# elif (feed_previous == True):
# loop_function = control_flow_ops.cond(mc_search,
# _mc_argmax_and_embed(embedding, output_projection, update_embedding_for_previous),
# _extract_argmax_and_embed(embedding, output_projection, update_embedding_for_previous))
emb_inp = [
embedding_ops.embedding_lookup(embedding, i) for i in decoder_inputs]
return attention_decoder(
emb_inp,
initial_state,
attention_states,
cell,
output_size=output_size,
num_heads=num_heads,
loop_function=loop_function,
initial_state_attention=initial_state_attention,
scope=scope)
def embedding_attention_seq2seq(encoder_inputs,
decoder_inputs,
cell,
num_encoder_symbols,
num_decoder_symbols,
embedding_size,
num_heads=1,
output_projection=None,
feed_previous=False,
dtype=None,
scope=None,
initial_state_attention=False,
mc_search=False):
with variable_scope.variable_scope(
scope or "embedding_attention_seq2seq", dtype=dtype) as scope:
dtype = scope.dtype
# Encoder.
encoder_cell = tf.contrib.rnn.EmbeddingWrapper(
cell, embedding_classes=num_encoder_symbols,
embedding_size=embedding_size)
encoder_outputs, encoder_state = tf.nn.static_rnn(
encoder_cell, encoder_inputs, dtype=dtype)
# First calculate a concatenation of encoder outputs to put attention on.
top_states = [array_ops.reshape(e, [-1, 1, cell.output_size])
for e in encoder_outputs]
attention_states = array_ops.concat(values=top_states, axis=1)
# Decoder.
output_size = None
if output_projection is None:
cell = rnn_cell.OutputProjectionWrapper(cell, num_decoder_symbols)
output_size = num_decoder_symbols
if isinstance(feed_previous, bool):
outputs, state = embedding_attention_decoder(
decoder_inputs,
encoder_state,
attention_states,
cell,
num_decoder_symbols,
embedding_size,
num_heads=num_heads,
output_size=output_size,
output_projection=output_projection,
feed_previous=feed_previous,
initial_state_attention=initial_state_attention,
mc_search=mc_search,
scope=scope)
return outputs, state, encoder_state
# If feed_previous is a Tensor, we construct 2 graphs and use cond.
def decoder(feed_previous_bool):
reuse = None if feed_previous_bool else True
with variable_scope.variable_scope(
variable_scope.get_variable_scope(), reuse=reuse) as scope:
outputs, state = embedding_attention_decoder(
decoder_inputs,
encoder_state,
attention_states,
cell,
num_decoder_symbols,
embedding_size,
num_heads=num_heads,
output_size=output_size,
output_projection=output_projection,
feed_previous=feed_previous_bool,
update_embedding_for_previous=False,
initial_state_attention=initial_state_attention,
mc_search=mc_search,
scope=scope)
state_list = [state]
if nest.is_sequence(state):
state_list = nest.flatten(state)
return outputs + state_list
outputs_and_state = control_flow_ops.cond(feed_previous,
lambda: decoder(True),
lambda: decoder(False))
outputs_len = len(decoder_inputs) # Outputs length same as decoder inputs.
state_list = outputs_and_state[outputs_len:]
state = state_list[0]
if nest.is_sequence(encoder_state):
state = nest.pack_sequence_as(structure=encoder_state,
flat_sequence=state_list)
return outputs_and_state[:outputs_len], state, encoder_state
def one2many_rnn_seq2seq(encoder_inputs,
decoder_inputs_dict,
cell,
num_encoder_symbols,
num_decoder_symbols_dict,
embedding_size,
feed_previous=False,
dtype=None,
scope=None):
"""One-to-many RNN sequence-to-sequence model (multi-task).
This is a multi-task sequence-to-sequence model with one encoder and multiple
decoders. Reference to multi-task sequence-to-sequence learning can be found
here: http://arxiv.org/abs/1511.06114
Args:
encoder_inputs: A list of 1D int32 Tensors of shape [batch_size].
decoder_inputs_dict: A dictionany mapping decoder name (string) to
the corresponding decoder_inputs; each decoder_inputs is a list of 1D
Tensors of shape [batch_size]; num_decoders is defined as
len(decoder_inputs_dict).
cell: rnn_cell.RNNCell defining the cell function and size.
num_encoder_symbols: Integer; number of symbols on the encoder side.
num_decoder_symbols_dict: A dictionary mapping decoder name (string) to an
integer specifying number of symbols for the corresponding decoder;
len(num_decoder_symbols_dict) must be equal to num_decoders.
embedding_size: Integer, the length of the embedding vector for each symbol.
feed_previous: Boolean or scalar Boolean Tensor; if True, only the first of
decoder_inputs will be used (the "GO" symbol), and all other decoder
inputs will be taken from previous outputs (as in embedding_rnn_decoder).
If False, decoder_inputs are used as given (the standard decoder case).
dtype: The dtype of the initial state for both the encoder and encoder
rnn cells (default: tf.float32).
scope: VariableScope for the created subgraph; defaults to
"one2many_rnn_seq2seq"
Returns:
A tuple of the form (outputs_dict, state_dict), where:
outputs_dict: A mapping from decoder name (string) to a list of the same
length as decoder_inputs_dict[name]; each element in the list is a 2D
Tensors with shape [batch_size x num_decoder_symbol_list[name]]
containing the generated outputs.
state_dict: A mapping from decoder name (string) to the final state of the
corresponding decoder RNN; it is a 2D Tensor of shape
[batch_size x cell.state_size].
"""
outputs_dict = {}
state_dict = {}
with variable_scope.variable_scope(
scope or "one2many_rnn_seq2seq", dtype=dtype) as scope:
dtype = scope.dtype
# Encoder.
encoder_cell = rnn_cell.EmbeddingWrapper(
cell, embedding_classes=num_encoder_symbols,
embedding_size=embedding_size)
_, encoder_state = rnn.rnn(encoder_cell, encoder_inputs, dtype=dtype)
# Decoder.
for name, decoder_inputs in decoder_inputs_dict.items():
num_decoder_symbols = num_decoder_symbols_dict[name]
with variable_scope.variable_scope("one2many_decoder_" + str(
name)) as scope:
decoder_cell = rnn_cell.OutputProjectionWrapper(cell,
num_decoder_symbols)
if isinstance(feed_previous, bool):
outputs, state = embedding_rnn_decoder(
decoder_inputs, encoder_state, decoder_cell, num_decoder_symbols,
embedding_size, feed_previous=feed_previous)
else:
# If feed_previous is a Tensor, we construct 2 graphs and use cond.
def filled_embedding_rnn_decoder(feed_previous):
"""The current decoder with a fixed feed_previous parameter."""
# pylint: disable=cell-var-from-loop
reuse = None if feed_previous else True
vs = variable_scope.get_variable_scope()
with variable_scope.variable_scope(vs, reuse=reuse):
outputs, state = embedding_rnn_decoder(
decoder_inputs, encoder_state, decoder_cell,
num_decoder_symbols, embedding_size,
feed_previous=feed_previous)
# pylint: enable=cell-var-from-loop
state_list = [state]
if nest.is_sequence(state):
state_list = nest.flatten(state)
return outputs + state_list
outputs_and_state = control_flow_ops.cond(
feed_previous,
lambda: filled_embedding_rnn_decoder(True),
lambda: filled_embedding_rnn_decoder(False))
# Outputs length is the same as for decoder inputs.
outputs_len = len(decoder_inputs)
outputs = outputs_and_state[:outputs_len]
state_list = outputs_and_state[outputs_len:]
state = state_list[0]
if nest.is_sequence(encoder_state):
state = nest.pack_sequence_as(structure=encoder_state,
flat_sequence=state_list)
outputs_dict[name] = outputs
state_dict[name] = state
return outputs_dict, state_dict
# def sequence_loss_by_mle(logits, targets, emb_dim, sequence_length, batch_size, name=None):
# pass
# if len(targets) != len(logits) or len(weights) != len(logits):
# raise ValueError("Lengths of logits, weights, and targets must be the same "
# "%d, %d, %d." % (len(logits), len(weights), len(targets)))
# with ops.name_scope(name, "sequence_loss_by_mle",
# logits + targets + weights):
#
# pretrain_loss = -tf.reduce_sum(
# tf.one_hot(tf.to_int32(tf.reshape(targets, [-1])), emb_dim, 1.0, 0.0) * tf.log(
# tf.clip_by_value(tf.reshape(logits, [-1, emb_dim]), 1e-20, 1.0)
# )
# ) / (sequence_length * batch_size)
#
#
#
# log_perp_list = []
# for logit, target, weight in zip(logits, targets, weights):
# pass
# def sequence_loss_by_example(logits, targets, weights,
# average_across_timesteps=True,
# softmax_loss_function=None,up_reward=None, policy_gradient=None, name=None):
# if len(targets) != len(logits) or len(weights) != len(logits):
# raise ValueError("Lengths of logits, weights, and targets must be the same "
# "%d, %d, %d." % (len(logits), len(weights), len(targets)))
# with ops.name_scope(name, "sequence_loss_by_example",
# logits + targets + weights):
# log_perp_list = []
# for logit, target, weight in zip(logits, targets, weights):
# if softmax_loss_function is None:
# # TODO(irving,ebrevdo): This reshape is needed because
# # sequence_loss_by_example is called with scalars sometimes, which
# # violates our general scalar strictness policy.
# target = array_ops.reshape(target, [-1])
# crossent = nn_ops.sparse_softmax_cross_entropy_with_logits(
# logit, target)
# else:
# #crossent = softmax_loss_function(logit, target)
# crossent = tf.cond(up_reward,
# lambda :policy_gradient(logit, target),
# lambda :softmax_loss_function(logit,target))
# log_perp_list.append(crossent * weight)
# log_perps = math_ops.add_n(log_perp_list)
# if average_across_timesteps:
# total_size = math_ops.add_n(weights)
# total_size += 1e-12 # Just to avoid division by 0 for all-0 weights.
# log_perps /= total_size
# return log_perps
def sequence_loss_by_example(logits, targets, weights,
average_across_timesteps=True,
softmax_loss_function=None, name=None):
if len(targets) != len(logits) or len(weights) != len(logits):
raise ValueError("Lengths of logits, weights, and targets must be the same "
"%d, %d, %d." % (len(logits), len(weights), len(targets)))
with ops.name_scope(name, "sequence_loss_by_example",
logits + targets + weights):
log_perp_list = []
for logit, target, weight in zip(logits, targets, weights):
if softmax_loss_function is None:
# TODO(irving,ebrevdo): This reshape is needed because
# sequence_loss_by_example is called with scalars sometimes, which
# violates our general scalar strictness policy.
target = array_ops.reshape(target, [-1])
crossent = nn_ops.sparse_softmax_cross_entropy_with_logits(
logit, target)
else:
crossent = softmax_loss_function(target, logit)
log_perp_list.append(crossent * weight)
log_perps = math_ops.add_n(log_perp_list)
if average_across_timesteps:
total_size = math_ops.add_n(weights)
total_size += 1e-12 # Just to avoid division by 0 for all-0 weights.
log_perps /= total_size
return log_perps
def sequence_loss(logits, targets, weights,
average_across_timesteps=True, average_across_batch=True,
softmax_loss_function=None, name=None):
"""Weighted cross-entropy loss for a sequence of logits, batch-collapsed.
Args:
logits: List of 2D Tensors of shape [batch_size x num_decoder_symbols].
targets: List of 1D batch-sized int32 Tensors of the same length as logits.
weights: List of 1D batch-sized float-Tensors of the same length as logits.
average_across_timesteps: If set, divide the returned cost by the total
label weight.
average_across_batch: If set, divide the returned cost by the batch size.
softmax_loss_function: Function (inputs-batch, labels-batch) -> loss-batch
to be used instead of the standard softmax (the default if this is None).
name: Optional name for this operation, defaults to "sequence_loss".
Returns:
A scalar float Tensor: The average log-perplexity per symbol (weighted).
Raises:
ValueError: If len(logits) is different from len(targets) or len(weights).
"""
with ops.name_scope(name, "sequence_loss", logits + targets + weights):
cost = math_ops.reduce_sum(sequence_loss_by_example(
logits, targets, weights,
average_across_timesteps=average_across_timesteps,
softmax_loss_function=softmax_loss_function))
if average_across_batch:
batch_size = array_ops.shape(targets[0])[0]
return cost / math_ops.cast(batch_size, cost.dtype)
else:
return cost
def sequence_loss_by_mle(logits, targets, vocab_size, sequence_length, batch_size, output_projection=None):
#print("logits: ", np.shape(logits[0]))
#logits: [seq_len, batch_size, emb_dim]
#targets: [seq_len, batch_size] =====transpose====> [batch_size, seq_len]
# labels = tf.to_int32(tf.transpose(targets))
#targets: [seq_len, batch_size] ====reshape[-1]====> [seq_len * batch_size]
labels = tf.to_int32(tf.reshape(targets, [-1]))
if output_projection is not None:
#logits = nn_ops.xw_plus_b(logits, output_projection[0], output_projection[1])
logits = [tf.matmul(logit, output_projection[0]) + output_projection[1] for logit in logits]
reshape_logits = tf.reshape(logits, [-1, vocab_size]) #[seq_len * batch_size, vocab_size]
prediction = tf.clip_by_value(reshape_logits, 1e-20, 1.0)
pretrain_loss = -tf.reduce_sum(
# [seq_len * batch_size , vocab_size]
tf.one_hot(labels, vocab_size, 1.0, 0.0) * tf.log(prediction)
) / (sequence_length * batch_size)
return pretrain_loss
def model_with_buckets(encoder_inputs, decoder_inputs, targets, weights, buckets, vocab_size, batch_size, seq2seq,
output_projection=None, softmax_loss_function=None, per_example_loss=False, name=None):
if len(encoder_inputs) < buckets[-1][0]:
raise ValueError("Length of encoder_inputs (%d) must be at least that of la"
"st bucket (%d)." % (len(encoder_inputs), buckets[-1][0]))
if len(targets) < buckets[-1][1]:
raise ValueError("Length of targets (%d) must be at least that of last"
"bucket (%d)." % (len(targets), buckets[-1][1]))
if len(weights) < buckets[-1][1]:
raise ValueError("Length of weights (%d) must be at least that of last"
"bucket (%d)." % (len(weights), buckets[-1][1]))
all_inputs = encoder_inputs + decoder_inputs + targets + weights
losses = []
outputs = []
encoder_states = []
with ops.name_scope(name, "model_with_buckets", all_inputs):
for j, bucket in enumerate(buckets):
with variable_scope.variable_scope(variable_scope.get_variable_scope(),
reuse=True if j > 0 else None):
bucket_outputs, decoder_states, encoder_state = seq2seq(encoder_inputs[:bucket[0]],
decoder_inputs[:bucket[1]])
outputs.append(bucket_outputs)
#print("bucket outputs: %s" %bucket_outputs)
encoder_states.append(encoder_state)
if per_example_loss:
losses.append(sequence_loss_by_example(
outputs[-1], targets[:bucket[1]], weights[:bucket[1]],
softmax_loss_function=softmax_loss_function))
else:
# losses.append(sequence_loss_by_mle(outputs[-1], targets[:bucket[1]], vocab_size, bucket[1], batch_size, output_projection))
losses.append(sequence_loss(outputs[-1], targets[:bucket[1]], weights[:bucket[1]], softmax_loss_function=softmax_loss_function))
return outputs, losses, encoder_states
