def __init__(self, embedding=None, vocab_size=None, hparams=None):
ModuleBase.__init__(self, hparams)
self._vocab_size = vocab_size
self._embedding = None
self.sampling_method = self._hparams.sampling_method
with tf.variable_scope(self.variable_scope):
if self._hparams.initializer:
tf.get_variable_scope().set_initializer( \
layers.get_initializer(self._hparams.initializer))
if self._hparams.position_embedder.name == 'sinusoids':
self.position_embedder = \
position_embedders.SinusoidsSegmentalPositionEmbedder( \
self._hparams.position_embedder.hparams)
if self._hparams.use_embedding:
if embedding is None and vocab_size is None:
raise ValueError("""If 'embedding' is not provided,
'vocab_size' must be specified.""")
if isinstance(embedding, (tf.Tensor, tf.Variable)):
self._embedding = embedding
else:
self._embedding = embedder_utils.get_embedding(
self._hparams.embedding,
embedding,
vocab_size,
variable_scope=self.variable_scope)
self._embed_dim = shape_list(self._embedding)[-1]
if self._hparams.zero_pad:
self._embedding = tf.concat( \
(tf.zeros(shape=[1, self._embed_dim]),\
self._embedding[1:, :]), 0)
if self._vocab_size is None:
self._vocab_size = self._embedding.get_shape().as_list()[0]
self.output_layer = \
self.build_output_layer(shape_list(self._embedding)[-1])
def dynamic_decode(self, template_input_pack,
encoder_decoder_attention_bias, segment_ids, offsets,
bos_id, eos_id):
"""
this function is called on in test mode, without the target input.
"""
with tf.variable_scope(self.variable_scope, reuse=True):
template = template_input_pack['templates']
template_word_embeds = tf.nn.embedding_lookup(
self._embedding, template)
batch_size = tf.shape(template)[0]
template_length = shape_list(template)[1]
channels = shape_list(template_word_embeds)[2]
template_pos_embeds = self.position_embedder(
template_length, channels, template_input_pack['segment_ids'],
template_input_pack['offsets'])
template_inputs = template_word_embeds + template_pos_embeds
# batch_size = tf.shape(template_inputs)[0]
beam_width = self._hparams.beam_width
maximum_decode_length = self.hparams.maximum_decode_length
start_tokens = tf.cast(tf.fill([batch_size], bos_id),
dtype=tf.int32)
if beam_width <= 1:
sampled_ids, log_probs = self.greedy_decode(
self.prepare_tokens_to_embeds,
start_tokens,
eos_id, #self._hparams.eos_idx,
decode_length=maximum_decode_length,
memory=template_inputs,
encoder_decoder_attention_bias=\
encoder_decoder_attention_bias,
segment_ids=segment_ids,
offsets=offsets,
)
else:
sampled_ids, log_probs = self.beam_decode(
self.prepare_tokens_to_embeds,
start_tokens,
eos_id, #self._hparams.eos_idx,
beam_width=beam_width,
decode_length=maximum_decode_length,
memory=template_inputs,
encoder_decoder_attention_bias=\
encoder_decoder_attention_bias,
segment_ids=segment_ids,
offsets=offsets
)
predictions = {'sampled_ids': sampled_ids, 'log_probs': log_probs}
return predictions
def _build(self, decoder_input_pack, template_input_pack,
encoder_decoder_attention_bias, args):
"""
this function is called on training generally.
Args:
targets: [bath_size, target_length], generally begins with [bos] token
template_input: [batch_size, source_length, channels]
segment_ids: [batch_size, source_length], which segment this word belongs to
outputs:
logits: [batch_size, target_length, vocab_size]
preds: [batch_size, target_length]
"""
input = decoder_input_pack['text_ids'][:, :-1]
decoder_self_attention_bias = (
attentions.attention_bias_lower_triangle(shape_list(input)[1]))
input_word_embeds = tf.nn.embedding_lookup(self._embedding, input)
if self._hparams.multiply_embedding_mode == 'sqrt_depth':
input_word_embeds = input_word_embeds * \
(self._embedding.shape.as_list()[-1]**0.5)
length = shape_list(input_word_embeds)[1]
channels = shape_list(input_word_embeds)[2]
input_pos_embeds = self.position_embedder(
length, channels, decoder_input_pack['segment_ids'][:, :-1],
decoder_input_pack['offsets'][:, :-1])
inputs = input_word_embeds + input_pos_embeds
template = template_input_pack['templates']
template_word_embeds = tf.nn.embedding_lookup(self._embedding,
template)
template_length = shape_list(template)[1]
template_pos_embeds = self.position_embedder(
template_length, channels, template_input_pack['segment_ids'],
template_input_pack['offsets'])
template_inputs = template_word_embeds + template_pos_embeds
self.decoder_output = self._self_attention_stack(
inputs,
template_inputs,
decoder_self_attention_bias=decoder_self_attention_bias,
)
logits = self.output_layer(self.decoder_output)
preds = tf.to_int32(tf.argmax(logits, axis=-1))
if not self._built:
self._add_internal_trainable_variables()
self._built = True
return logits, preds
def step(self, time, inputs, state, name=None):
cell_outputs, cell_state = self._cell(inputs, state)
logits = self._output_layer(
cell_outputs) # turn cell outputs into logits for for each vocab
sample_ids = self._helper.sample( # turn logits into ids
time=time,
outputs=logits,
state=cell_state)
(finished, next_inputs_word_embeds,
next_state) = self._helper.next_inputs(
time=time,
outputs=logits,
state=cell_state,
sample_ids=sample_ids) # look up in embedding -> next_inputs
batch_size, channels = shape_list(next_inputs_word_embeds)
next_input_pos_embeds = self.position_embedder(
length=1,
channels=channels,
segment_ids=tf.cast(tf.fill([batch_size, 1],
self.current_segment_id),
dtype=tf.int64),
offsets=tf.cast(tf.fill([batch_size, 1], time), dtype=tf.int64))
next_input_pos_embeds = tf.reshape(next_input_pos_embeds,
[batch_size, channels])
next_inputs = next_inputs_word_embeds + next_input_pos_embeds
outputs = BasicRNNDecoderOutput(logits, sample_ids, cell_outputs)
return (outputs, next_state, next_inputs, finished)
def __init__(self, inputs, sequence_length, time_major=False, name=None):
"""Initializer.
Args:
inputs: A (structure of) input tensors.
sequence_length: An int32 vector tensor.
time_major: Python bool. Whether the tensors in `inputs` are time major.
If `False` (default), they are assumed to be batch major.
name: Name scope for any created operations.
Raises:
ValueError: if `sequence_length` is not a 1D tensor.
"""
with ops.name_scope(name, "TrainingHelper", [inputs, sequence_length]):
inputs = ops.convert_to_tensor(inputs, name="inputs")
self._inputs = inputs
if not time_major:
inputs = nest.map_structure(_transpose_batch_time, inputs)
self._input_tas = nest.map_structure(_unstack_ta, inputs)
self._sequence_length = ops.convert_to_tensor(
sequence_length, name="sequence_length")
if self._sequence_length.get_shape().ndims != 1:
raise ValueError(
"Expected sequence_length to be a vector, but received shape: %s" %
self._sequence_length.get_shape())
self._zero_inputs = nest.map_structure(
lambda inp: array_ops.zeros_like(inp[0, :]), inputs)
self._batch_size = shape_list(sequence_length)[0]
def _symbols_to_logits_fn(self, embedding_fn, max_length):
"""Returns a function that accepts the decoded tokens and related
decoding status, and returns the logits of next token.
"""
channels = shape_list(self._embedding)[-1]
timing_signal = self.position_embedder(max_length, channels)
def _impl(ids, step, cache):
"""The function is called in dynamic decoding.
`ids` should be next_id of shape `[batch_size, decoded_lenth]`
Returned logits is of shape `[batch_size, 1]`
"""
ids = ids[:, -1:]
inputs = embedding_fn(ids)
# Multiply embedding by sqrt of its dimention
inputs *= self._embedding.shape.as_list()[-1]**0.5
inputs += timing_signal[:, step:step+1]
outputs = self._self_attention_stack(
inputs,
memory=cache['memory'],
cache=cache,
)
logits = self.output_layer(outputs)
logits = tf.squeeze(logits, axis=[1])
return logits, cache
return _impl
def _symbols_to_logits_fn(self, embedding_fn, max_length, segment_ids,
offsets):
channels = shape_list(self._embedding)[-1]
timing_signal = self.position_embedder(max_length, channels,
segment_ids, offsets)
""" the function is normally called in dynamic decoding mode.
the ids should be `next_id` with the shape [batch_size, 1]
the returned logits is [batch_size, 1]
"""
def _impl(ids, step, cache):
ids = ids[:, -1:]
decoder_self_attention_bias = (
attentions.attention_bias_lower_triangle(shape_list(ids)[1]))
inputs = embedding_fn(ids)
if self._hparams.multiply_embedding_mode == 'sqrt_depth':
inputs *= self._embedding.shape.as_list()[-1]**0.5
else:
assert NotImplementedError
inputs += timing_signal[:, step:step + 1]
outputs = self._self_attention_stack(
inputs,
template_input=cache['memory'],
cache=cache,
decoder_self_attention_bias=decoder_self_attention_bias,
)
logits = self.output_layer(outputs)
logits = tf.squeeze(logits, axis=[1])
return logits, cache
return _impl
def _make_output_layer(output_layer, vocab_size, output_layer_bias,
variable_scope):
"""Makes a decoder output layer.
"""
_vocab_size = vocab_size
if is_callable(output_layer):
_output_layer = output_layer
elif tf.contrib.framework.is_tensor(output_layer):
_vocab_size = shape_list(output_layer)[1]
_output_layer = _make_output_layer_from_tensor(output_layer,
_vocab_size,
output_layer_bias,
variable_scope)
elif output_layer is None:
if _vocab_size is None:
raise ValueError(
"Either `output_layer` or `vocab_size` must be provided. "
"Set `output_layer=tf.identity` if no output layer is "
"wanted.")
with tf.variable_scope(variable_scope):
# pylint: disable=redefined-variable-type
_output_layer = tf.layers.Dense(units=_vocab_size,
use_bias=output_layer_bias)
else:
raise ValueError(
"output_layer should be a callable layer, a tensor, or None. "
"Unsupported type: ", type(output_layer))
return _output_layer, _vocab_size
def _compute_embeddings(self, positions):
inv_timescales = self.inv_timescales
scaled_time = tf.reshape(tf.cast(positions, inv_timescales.dtype),
(-1, 1)) * tf.expand_dims(inv_timescales, 0)
signal = tf.concat([tf.sin(scaled_time), tf.cos(scaled_time)], axis=1)
signal = tf.pad(signal, [[0, 0], [0, tf.mod(self._dim, 2)]])
signal = tf.reshape(signal, shape_list(positions) + [self._dim])
return signal
def _outputs_to_logits(outputs):
shape = shape_list(outputs)
outputs = tf.reshape(outputs, [-1, dim])
logits = tf.matmul(outputs, self._embedding, transpose_b=True)
if affine_bias is not None:
logits += affine_bias
logits = tf.reshape(logits, shape[:-1] + [self._vocab_size])
return logits
def __init__(self, embedding, hparams=None):
ModuleBase.__init__(self, hparams)
with tf.variable_scope(self.variable_scope):
if self._hparams.initializer:
tf.get_variable_scope().set_initializer(
layers.get_initializer(self._hparams.initializer))
if self._hparams.position_embedder_type == 'sinusoids':
self.position_embedder = SinusoidsPositionEmbedder(
self._hparams.position_embedder_hparams)
else:
self.position_embedder = PositionEmbedder(
position_size=self._hparams.position_size,
hparams=self._hparams.position_embedder_hparams)
self._embedding = embedding
self._vocab_size = self._embedding.get_shape().as_list()[0]
self.output_layer = \
self._build_output_layer(shape_list(self._embedding)[-1])
self.multihead_attentions = {'self_att': [], 'encdec_att': []}
self.poswise_networks = []
for i in range(self._hparams.num_blocks):
layer_name = 'layer_{}'.format(i)
with tf.variable_scope(layer_name):
with tf.variable_scope("self_attention"):
multihead_attention = MultiheadAttentionEncoder(
self._hparams.multihead_attention)
self.multihead_attentions['self_att'].append(
multihead_attention)
# pylint: disable=protected-access
if self._hparams.dim != \
multihead_attention._hparams.output_dim:
raise ValueError('The output dimenstion of '
'MultiheadEncoder should be equal '
'to the dim of TransformerDecoder')
with tf.variable_scope('encdec_attention'):
multihead_attention = MultiheadAttentionEncoder(
self._hparams.multihead_attention)
self.multihead_attentions['encdec_att'].append(
multihead_attention)
if self._hparams.dim != \
multihead_attention._hparams.output_dim:
raise ValueError('The output dimenstion of '
'MultiheadEncoder should be equal '
'to the dim of TransformerDecoder')
poswise_network = FeedForwardNetwork(
hparams=self._hparams['poswise_feedforward'])
if self._hparams.dim != \
poswise_network._hparams.layers[-1]['kwargs']['units']:
raise ValueError('The output dimenstion of '
'FeedForwardNetwork should be equal '
'to the dim of TransformerDecoder')
self.poswise_networks.append(poswise_network)
def _expand_to_beam_width(self, tensor, beam_width):
"""
:param tensor: [batch_size, max_len]
:param beam_width:
:return: [batch_size*beam_width, max_len]
"""
batch_size = shape_list(tensor)[0]
expanded = tf.tile(tf.expand_dims(tensor, axis=1), [1, beam_width, 1])
return tf.reshape(expanded, [batch_size * beam_width, -1])
def _split_heads(self, x):
"""Split channels (dimension 2) into multiple heads,
becomes dimension 1).
Must ensure `x.shape[-1]` can be deviced by num_heads
"""
depth = shape_list(x)[-1]
splitted_x = tf.reshape(x, [tf.shape(x)[0], tf.shape(x)[1], \
self._hparams.num_heads, depth // self._hparams.num_heads])
return tf.transpose(splitted_x, [0, 2, 1, 3])
def _outputs_to_logits(outputs):
shape = shape_list(outputs)
dim = shape[-1]
outputs = tf.reshape(outputs, [-1, dim])
logits = tf.matmul(outputs, output_layer_tensor)
if affine_bias is not None:
logits += affine_bias
logits = tf.reshape(logits, shape[:-1] + [vocab_size])
return logits
def _combine_heads(self, x):
"""
Args:
x: A Tensor of shape `[batch, num_heads, seq_len, dim]`
Returns:
A Tensor of shape `[batch, seq_len, num_heads * dim]`
"""
t = tf.transpose(x, [0, 2, 1, 3]) #[batch, seq_len, num_heads, dim]
num_heads, dim = shape_list(t)[-2:]
assert num_heads == self._hparams.num_heads
return tf.reshape(t, [tf.shape(t)[0], tf.shape(t)[1], num_heads*dim])
def _build(self, decoder_input, encoder_output, \
encoder_decoder_attention_bias, mode=None):
"""
this function is called on training generally.
Args:
targets: [bath_size, target_length], generally begins with [bos] token
encoder_output: [batch_size, source_length, channels]
outputs:
logits: [batch_size, target_length, vocab_size]
preds: [batch_size, target_length]
"""
logits = None
decoder_self_attention_bias = (
attentions.attention_bias_lower_triangle(
shape_list(decoder_input)[1]))
target_inputs = tf.nn.embedding_lookup(self._embedding, decoder_input)
if self._hparams.multiply_embedding_mode == 'sqrt_depth':
target_inputs = target_inputs * \
(self._embedding.shape.as_list()[-1]**0.5)
lengths = shape_list(target_inputs)[1]
channels = shape_list(target_inputs)[2]
pos_embeds = self.position_embedder(lengths, channels)
inputs = target_inputs + pos_embeds
self.decoder_output = self._self_attention_stack(
inputs,
encoder_output,
decoder_self_attention_bias=decoder_self_attention_bias,
encoder_decoder_attention_bias=encoder_decoder_attention_bias,
cache=None,
mode=None,
)
logits = self.output_layer(self.decoder_output)
preds = tf.to_int32(tf.argmax(logits, axis=-1))
if not self._built:
self._add_internal_trainable_variables()
self._built = True
return logits, preds
def _merge_beam_dim(tensor):
"""Reshapes first two dimensions in to single dimension.
Args:
tensor: Tensor to reshape of shape [A, B, ...]
Returns:
Reshaped tensor of shape [A*B, ...]
"""
shape = shape_list(tensor)
shape[0] *= shape[1] # batch -> batch * beam_size
shape.pop(1) # Remove beam dim
return tf.reshape(tensor, shape)
def _unmerge_beam_dim(tensor, batch_size, beam_size):
"""Reshapes first dimension back to [batch_size, beam_size].
Args:
tensor: Tensor to reshape of shape [batch_size*beam_size, ...]
batch_size: Tensor, original batch size.
beam_size: int, original beam size.
Returns:
Reshaped tensor of shape [batch_size, beam_size, ...]
"""
shape = shape_list(tensor)
new_shape = [batch_size] + [beam_size] + shape[1:]
return tf.reshape(tensor, new_shape)
def __init__(self, embedding, hparams=None):
ModuleBase.__init__(self, hparams)
with tf.variable_scope(self.variable_scope):
if self._hparams.initializer:
tf.get_variable_scope().set_initializer( \
layers.get_initializer(self._hparams.initializer))
self.position_embedder = \
SinusoidsPositionEmbedder(
self._hparams.position_embedder_hparams)
self._embedding = embedding
self._vocab_size = self._embedding.get_shape().as_list()[0]
self.output_layer = \
self._build_output_layer(shape_list(self._embedding)[-1])
def __init__(self, embedding, start_tokens, end_token):
"""Initializer.
Args:
embedding: A callable or the `params` argument for `embedding_lookup`.
If a callable, it can take a vector tensor of `ids` (argmax ids),
or take two arguments (`ids`, `times`), where `ids` is a vector
tensor of argmax ids, and `times` is a vector tensor of current
time steps (i.e., position ids). The latter case can be used when
attr:`embedding` is a combination of word embedding and position
embedding.
The returned tensor will be returned by :meth:`next_inputs`.
start_tokens: `int32` vector shaped `[batch_size]`, the start tokens.
end_token: `int32` scalar, the token that marks end of decoding.
Raises:
ValueError: if `start_tokens` is not a 1D tensor or `end_token` is not a
scalar.
"""
if callable(embedding):
self._embedding_fn = embedding
else:
self._embedding_fn = (
lambda ids: embedding_ops.embedding_lookup(embedding, ids))
self._start_tokens = ops.convert_to_tensor(
start_tokens, dtype=dtypes.int32, name="start_tokens")
self._end_token = ops.convert_to_tensor(
end_token, dtype=dtypes.int32, name="end_token")
if self._start_tokens.get_shape().ndims != 1:
raise ValueError("start_tokens must be a vector")
self._batch_size = shape_list(start_tokens)[0]
if self._end_token.get_shape().ndims != 0:
raise ValueError("end_token must be a scalar")
self._embedding_args_cnt = len(get_args(self._embedding_fn))
if self._embedding_args_cnt == 1:
self._start_inputs = self._embedding_fn(self._start_tokens)
elif self._embedding_args_cnt == 2:
# Position index is 0 in the beginning
times = tf.zeros([self._batch_size], dtype=tf.int32)
self._start_inputs = self._embedding_fn(self._start_tokens, times)
else:
raise ValueError('`embedding` should expect 1 or 2 arguments.')
def _input_ids_to_outputs(self, input_ids, step, cache):
"""The function is called in beam-search decoding.
`inputs` should be of shape `[batch_size]`.
Returns outputs (i.e. logits) of shape `[batch_size, vocab_size]`
and updated cache.
"""
_batch_size = shape_list(input_ids)[0]
times = tf.ones([_batch_size], dtype=tf.int32) * step
inputs = self.embedding(input_ids, times)
outputs = self._self_attention_stack(
tf.expand_dims(inputs, axis=1),
memory=cache.get('memory'),
cache=cache,
)
outputs = self._output_layer(outputs)
outputs = tf.squeeze(outputs, axis=[1])
return outputs, cache
def _impl(ids, step, cache):
ids = ids[:, -1:]
decoder_self_attention_bias = (
attentions.attention_bias_lower_triangle(shape_list(ids)[1]))
inputs = embedding_fn(ids)
if self._hparams.multiply_embedding_mode == 'sqrt_depth':
inputs *= self._embedding.shape.as_list()[-1]**0.5
else:
assert NotImplementedError
inputs += timing_signal[:, step:step + 1]
outputs = self._self_attention_stack(
inputs,
template_input=cache['memory'],
cache=cache,
decoder_self_attention_bias=decoder_self_attention_bias,
)
logits = self.output_layer(outputs)
logits = tf.squeeze(logits, axis=[1])
return logits, cache
def _build(self, inputs, sequence_length, mode=None):
"""Encodes the inputs.
Args:
inputs: A 3D Tensor of shape `[batch_size, max_time, dim]`,
containing the word embeddings of input sequences. Note that
the embedding dimension `dim` must equal "dim" in
:attr:`hparams`.
sequence_length: A 1D Tensor of shape `[batch_size]`. Input tokens
beyond respective sequence lengths are masked out
automatically.
mode (optional): A tensor taking value in
:tf_main:`tf.estimator.ModeKeys <estimator/ModeKeys>`,
including `TRAIN`, `EVAL`, and `PREDICT`. Used to toggle
dropout.
If `None` (default), :func:`texar.global_mode` is used.
Returns:
A Tensor of shape `[batch_size, max_time, dim]` containing the
encoded vectors.
"""
# Multiply input embedding with the sqrt of its dimension for
# normalization
inputs = inputs * self._hparams.dim**0.5
inputs = mask_sequences(inputs, sequence_length, tensor_rank=3)
_, lengths, _ = shape_list(inputs)
inputs_padding = 1 - tf.sequence_mask(
sequence_length, tf.shape(inputs)[1], dtype=tf.float32)
ignore_padding = attn.attention_bias_ignore_padding(inputs_padding)
encoder_self_attention_bias = ignore_padding
pos_embeds = self.position_embedder(lengths, self._hparams.dim)
input_embedding = inputs + pos_embeds
x = tf.layers.dropout(input_embedding,
rate=self._hparams.embedding_dropout,
training=is_train_mode(mode))
pad_remover = utils.transformer_utils.PadRemover(inputs_padding)
for i in range(self._hparams.num_blocks):
with tf.variable_scope("layer_{}".format(i)):
with tf.variable_scope('self_attention'):
selfatt_output = attn.multihead_attention(
queries=layers.layer_normalize(x),
memory=None,
memory_attention_bias=encoder_self_attention_bias,
num_heads=self._hparams.num_heads,
dropout_rate=self._hparams.attention_dropout,
num_units=self._hparams.dim,
scope='multihead_attention')
x = x + tf.layers.dropout(
selfatt_output,
rate=self._hparams.residual_dropout,
training=is_train_mode(mode),
)
poswise_network = FeedForwardNetwork(
hparams=self._hparams['poswise_feedforward'])
with tf.variable_scope(poswise_network.variable_scope):
y = layers.layer_normalize(x)
original_shape = shape_list(y)
y = tf.reshape(y, [-1, self._hparams.dim])
y = tf.expand_dims(pad_remover.remove(y), axis=0)
# [1, batch_size*seq_length, hidden_dim]
sub_output = tf.layers.dropout(
poswise_network(y),
rate=self._hparams.residual_dropout,
training=is_train_mode(mode))
sub_output = tf.reshape(pad_remover.restore(tf.squeeze(\
sub_output, axis=0)), original_shape \
)
x = x + sub_output
encoder_output = layers.layer_normalize(x)
if not self._built:
self._add_internal_trainable_variables()
self._built = True
return encoder_output
def _build(self, # pylint: disable=arguments-differ
memory,
memory_sequence_length=None,
memory_attention_bias=None,
inputs=None,
sequence_length=None,
decoding_strategy='train_greedy',
beam_width=1,
alpha=0,
start_tokens=None,
end_token=None,
max_decoding_length=None,
mode=None):
"""Performs decoding.
The decoder supports 4 decoding strategies. For the first 3 strategies,
set :attr:`decoding_strategy` to the respective string.
- **"train_greedy"**: decoding in teacher-forcing fashion \
(i.e., feeding \
ground truth to decode the next step), and for each step sample \
is obtained by taking the `argmax` of logits. \
Argument :attr:`inputs` is required for this strategy. \
:attr:`sequence_length` is optional.
- **"infer_greedy"**: decoding in inference fashion (i.e., feeding \
`generated` sample to decode the next step), and for each
step sample is obtained by taking the `argmax` of logits.\
Arguments :attr:`(start_tokens, end_token)` are \
required for this strategy, and argument \
:attr:`max_decoding_length` is optional.
- **"infer_sample"**: decoding in inference fashion, and for each step\
sample is obtained by `random sampling` from the logits.
Arguments :attr:`(start_tokens, end_token)` are \
required for this strategy, and argument \
:attr:`max_decoding_length` is optional.
- **Beam Search**: set :attr:`beam_width` to > 1 to use beam search \
decoding.\
Arguments :attr:`(start_tokens, end_token)` are \
required, and argument \
:attr:`max_decoding_length` is optional.
Args:
memory: The memory to attend, e.g., the output of an RNN encoder.
A Tensor of shape `[batch_size, memory_max_time, dim]`.
memory_sequence_length (optional): A Tensor of shape `[batch_size]`
containing the sequence lengths for the batch entries in
memory. Used to create attention bias of
:attr:`memory_attention_bias` is not given. Ignored if
`memory_attention_bias` is provided.
memory_attention_bias (optional): A Tensor of shape
`[batch_size, num_heads, memory_max_time, dim]`.
An attention bias typically sets the value of a padding
position to a large negative value for masking. If not given,
:attr:`memory_sequence_length` is used to automatically
create an attention bias.
inputs (optional): Input tensor for teacher forcing decoding, of
shape `[batch_size, target_max_time, emb_dim]` containing the
target sequence word embeddings.
Used when :attr:`decoding_strategy` is set to "train_greedy".
sequence_length (optional): A Tensor of shape `[batch_size]`,
containing the sequence length of :attr:`inputs`.
Tokens beyond the respective sequence length are masked out.
Used when :attr:`decoding_strategy` is set to
"train_greedy".
decoding_strategy (str): A string specifying the decoding
strategy, including "train_greedy", "infer_greedy",
"infer_sample".
Different arguments are required based on the
strategy. See above for details. Ignored if
:attr:`beam_width` > 1.
beam_width (int): Set to > 1 to use beam search.
alpha (float): Length penalty coefficient.
Refer to https://arxiv.org/abs/1609.08144
for more details.
tart_tokens (optional): An int Tensor of shape `[batch_size]`,
containing the start tokens.
Used when `decoding_strategy` = "infer_greedy" or
"infer_sample", or `beam_width` > 1.
end_token (optional): An int 0D Tensor, the token that marks end
of decoding.
Used when `decoding_strategy` = "infer_greedy" or
"infer_sample", or `beam_width` > 1.
max_decoding_length (optional): An int scalar Tensor indicating
the maximum allowed number of decoding steps.
If `None` (default), use "max_decoding_length" defined in
:attr:`hparams`. Ignored in "train_greedy" decoding.
mode (optional): A tensor taking value in
:tf_main:`tf.estimator.ModeKeys <estimator/ModeKeys>`, including
`TRAIN`, `EVAL`, and `PREDICT`. Controls dropout mode.
If `None` (default), :func:`texar.global_mode`
is used.
Returns:
- For **"train_greedy"** decoding, returns an instance of \
:class:`~texar.modules.TransformerDecoderOutput` which contains\
`sample_id` and `logits`.
- For **"infer_greedy"** and **"infer_sample"** decoding, returns\
a tuple `(outputs, sequence_lengths)`, where `outputs` is an \
instance of :class:`~texar.modules.TransformerDecoderOutput` as\
in "train_greedy", and `sequence_lengths` is a Tensor of shape\
`[batch_size]` containing the length of each sample.
- For **beam_search** decoding, returns a `dict` containing keys\
"sample_id" and "log_prob".
- **"sample_id"** is an int Tensor of shape \
`[batch_size, max_time, beam_width]` containing generated\
token indexes. `sample_id[:,:,0]` is the highest-probable \
sample.
- **"log_porb"** is a float Tensor of shape \
`[batch_size, beam_width]` containing the log probability \
of each sequence sample.
"""
if memory_attention_bias is None:
if memory_sequence_length is None:
raise ValueError(
"`memory_sequence_length` is required if "
"`memory_attention_bias` is not given.")
#enc_padding = 1 - mask_sequences(tf.ones_like(memory),
# memory_sequence_length,
# tensor_rank=3)[:, :, 0]
enc_padding = 1 - tf.sequence_mask(
memory_sequence_length, tf.shape(memory)[1], dtype=tf.float32)
memory_attention_bias = attn.attention_bias_ignore_padding(
enc_padding)
if beam_width <= 1 and decoding_strategy == 'train_greedy':
if sequence_length is not None:
inputs = mask_sequences(inputs, sequence_length, tensor_rank=3)
decoder_self_attention_bias = (
attn.attention_bias_lower_triangle(
shape_list(inputs)[1]))
target_inputs = inputs * self._hparams.dim**0.5
_, lengths, channels = shape_list(target_inputs)
pos_embeds = self.position_embedder(lengths, channels)
inputs = target_inputs + pos_embeds
decoder_output = self._self_attention_stack(
inputs,
memory,
decoder_self_attention_bias=decoder_self_attention_bias,
memory_attention_bias=memory_attention_bias,
cache=None,
mode=mode)
logits = self.output_layer(decoder_output)
preds = tf.to_int32(tf.argmax(logits, axis=-1))
output = TransformerDecoderOutput(
logits=logits,
sample_id=preds
)
rets = output
else: # Inference decoding
if max_decoding_length is None:
max_decoding_length = self._hparams.max_decoding_length
if beam_width <= 1:
logits, preds, sequence_length = self._infer_decoding(
self._prepare_tokens_to_embeds,
start_tokens,
end_token,
decode_length=max_decoding_length,
memory=memory,
memory_attention_bias=memory_attention_bias,
decoding_strategy=decoding_strategy,
)
output = TransformerDecoderOutput(
logits=logits,
sample_id=preds)
rets = output, sequence_length
else:
# The output format is different when running beam search
sample_id, log_prob = self._beam_decode(
self._prepare_tokens_to_embeds,
start_tokens,
end_token,
beam_width=beam_width,
alpha=alpha,
decode_length=max_decoding_length,
memory=memory,
memory_attention_bias=memory_attention_bias,
)
predictions = {
'sample_id':sample_id,
'log_prob': log_prob
}
rets = predictions
if not self._built:
self._add_internal_trainable_variables()
self._built = True
return rets
def _build(self, inputs, sequence_length, mode=None):
"""Encodes the inputs.
Args:
inputs: A 3D Tensor of shape `[batch_size, max_time, dim]`,
containing the word embeddings of input sequences. Note that
the embedding dimension `dim` must equal "dim" in
:attr:`hparams`.
sequence_length: A 1D Tensor of shape `[batch_size]`. Input tokens
beyond respective sequence lengths are masked out
automatically.
mode (optional): A tensor taking value in
:tf_main:`tf.estimator.ModeKeys <estimator/ModeKeys>`,
including `TRAIN`, `EVAL`, and `PREDICT`. Used to toggle
dropout.
If `None` (default), :func:`texar.global_mode` is used.
Returns:
A Tensor of shape `[batch_size, max_time, dim]` containing the
encoded vectors.
"""
# Multiply input embedding with the sqrt of its dimension for
# normalization
if not self._hparams.use_bert_config:
inputs = inputs * self._hparams.dim**0.5
inputs = mask_sequences(inputs, sequence_length, tensor_rank=3)
_, lengths, _ = shape_list(inputs)
inputs_padding = 1 - tf.sequence_mask(
sequence_length, tf.shape(inputs)[1], dtype=tf.float32)
if self._hparams.use_bert_config:
ignore_padding = attn.attention_bias_ignore_padding(
inputs_padding, bias_value=-1e4)
else:
ignore_padding = attn.attention_bias_ignore_padding(
inputs_padding)
encoder_self_attention_bias = ignore_padding
positions = tf.expand_dims(tf.range(lengths, dtype=tf.int32), 0)
pos_embeds = self.position_embedder(positions)
input_embedding = inputs + pos_embeds
if self._hparams.use_bert_config:
x = layers.layer_normalize(input_embedding)
x = tf.layers.dropout(x,
rate=self._hparams.embedding_dropout,
training=is_train_mode(mode))
else:
x = tf.layers.dropout(input_embedding,
rate=self._hparams.embedding_dropout,
training=is_train_mode(mode))
# Just to keep consistent with BERT, actually makes no difference
if self._hparams.use_bert_config:
pad_remover = None
else:
pad_remover = utils.transformer_utils.PadRemover(inputs_padding)
for i in range(self._hparams.num_blocks):
with tf.variable_scope("layer_{}".format(i)):
multihead_attention = self.multihead_attention_list[i]
# trivial difference between BERT and original Transformer
if self._hparams.use_bert_config:
_queries_input = x
else:
_queries_input = layers.layer_normalize(x)
attention_output = multihead_attention(
queries=_queries_input,
memory=_queries_input,
memory_attention_bias=encoder_self_attention_bias,
mode=mode,
)
attention_output = tf.layers.dropout(
attention_output,
rate=self._hparams.residual_dropout,
training=is_train_mode(mode),
)
x = x + attention_output
with tf.variable_scope('output'):
if self._hparams.use_bert_config:
x = layers.layer_normalize(x)
y = x
else:
y = layers.layer_normalize(x)
poswise_network = self.poswise_networks[i]
with tf.variable_scope(poswise_network.variable_scope):
original_shape = shape_list(y)
y = tf.reshape(y, [-1, self._hparams.dim])
if pad_remover:
y = tf.expand_dims(pad_remover.remove(y), axis=0)
# [1, batch_size*seq_length, hidden_dim]
layer_output = poswise_network(y, mode=mode)
sub_output = tf.layers.dropout(
layer_output,
rate=self._hparams.residual_dropout,
training=is_train_mode(mode)
)
if pad_remover:
sub_output = tf.reshape(pad_remover.restore(tf.squeeze(\
sub_output, axis=0)), original_shape \
)
else:
sub_output = tf.reshape(sub_output, original_shape)
x = x + sub_output
if self._hparams.use_bert_config:
x = layers.layer_normalize(x)
if not self._hparams.use_bert_config:
x = layers.layer_normalize(x)
if not self._built:
self._add_internal_trainable_variables()
self._built = True
return x
def _build(
self, # pylint: disable=arguments-differ, too-many-statements
decoding_strategy='train_greedy',
inputs=None,
adjs=None,
memory=None,
memory_sequence_length=None,
memory_attention_bias=None,
beam_width=None,
length_penalty=0.,
start_tokens=None,
end_token=None,
context=None,
context_sequence_length=None,
softmax_temperature=None,
max_decoding_length=None,
impute_finished=False,
embedding=None,
helper=None,
mode=None):
"""Performs decoding.
See 'Texar.modules.decoders.transformer_decoders.TransformerDecoder' for details
adjs: A 3D Tensor of shape `[batch_size, max_time, max_time]`,
containing the adjacency matrices of input sequences
"""
# Get adjacency masks from adjs
self.adj_masks = 1 - tf.cast(tf.equal(adjs, 0), dtype=tf.float32)
if memory is not None:
if memory_attention_bias is None:
if memory_sequence_length is None:
raise ValueError("`memory_sequence_length` is required if "
"`memory_attention_bias` is not given.")
enc_padding = 1 - tf.sequence_mask(memory_sequence_length,
shape_list(memory)[1],
dtype=tf.float32)
memory_attention_bias = attn.attention_bias_ignore_padding(
enc_padding)
# record the context, which will be used in step function
# for dynamic_decode
if context is not None:
start_tokens = context[:, 0]
self.context = context[:, 1:]
self.context_sequence_length = context_sequence_length - 1
else:
self.context = None
self.embedding = embedding
if helper is None and beam_width is None and \
decoding_strategy == 'train_greedy': # Teacher-forcing
decoder_self_attention_bias = (attn.attention_bias_lower_triangle(
shape_list(inputs)[1]))
decoder_output = self._self_attention_stack(
inputs,
memory,
decoder_self_attention_bias=decoder_self_attention_bias,
memory_attention_bias=memory_attention_bias,
cache=None,
mode=mode)
logits = self._output_layer(decoder_output)
preds = tf.to_int32(tf.argmax(logits, axis=-1))
rets = TransformerDecoderOutput(logits=logits, sample_id=preds)
else:
if max_decoding_length is None:
max_decoding_length = self._hparams.max_decoding_length
self.max_decoding_length = max_decoding_length
if beam_width is None: # Inference-like decoding
# Prepare helper
if helper is None:
if decoding_strategy == "infer_greedy":
helper = tx_helper.GreedyEmbeddingHelper(
embedding, start_tokens, end_token)
elif decoding_strategy == "infer_sample":
helper = tx_helper.SampleEmbeddingHelper(
embedding, start_tokens, end_token,
softmax_temperature)
else:
raise ValueError(
"Unknown decoding strategy: {}".format(
decoding_strategy))
self._helper = helper
self._cache = self._init_cache(memory,
memory_attention_bias,
beam_search_decoding=False)
if context is not None:
self.context = tf.pad(self.context, [[
0, 0
], [0, max_decoding_length - shape_list(self.context)[1]]])
outputs, _, sequence_lengths = dynamic_decode(
decoder=self,
impute_finished=impute_finished,
maximum_iterations=max_decoding_length,
output_time_major=False,
scope=self.variable_scope)
if context is not None:
# Here the length of sample_id will be larger than that
# of logit by 1, because there will be a additional
# start_token in the returned sample_id.
# the start_id should be the first token of the
# given context
outputs = TransformerDecoderOutput(
logits=outputs.logits,
sample_id=tf.concat([
tf.expand_dims(start_tokens, 1), outputs.sample_id
],
axis=1))
sequence_lengths = sequence_lengths + 1
rets = outputs, sequence_lengths
else: # Beam-search decoding
# Ignore `decoding_strategy`; Assume `helper` is not set
if helper is not None:
raise ValueError("Must not set 'beam_width' and 'helper' "
"simultaneously.")
_batch_size = shape_list(start_tokens)[0]
self._cache = self._init_cache(memory,
memory_attention_bias,
beam_search_decoding=True,
batch_size=_batch_size)
# The output format is different when running beam search
sample_id, log_prob = self._beam_decode(
start_tokens,
end_token,
beam_width=beam_width,
length_penalty=length_penalty,
decode_length=max_decoding_length,
)
rets = {'sample_id': sample_id, 'log_prob': log_prob}
if not self._built:
self._add_internal_trainable_variables()
self._built = True
return rets
def _build(self,
inputs,
memory,
sequence_length,
memory_sequence_length,
adjs,
encoder_output,
mode=None):
"""Encodes the inputs.
Args:
inputs: A 3D Tensor of shape `[batch_size, max_time, dim]`,
containing the embedding of input sequences. Note that
the embedding dimension `dim` must equal "dim" in
:attr:`hparams`. The input embedding is typically an aggregation
of word embedding and position embedding.
memory: A 3D Tensor of shape `[batch_size, memory_max_time, dim]`,
containing the embedding of memory sequences. Note that
the embedding dimension `dim` must equal "dim" in
:attr:`hparams`. The input embedding is typically an aggregation
of word embedding and position embedding.
sequence_length: A 1D Tensor of shape `[batch_size]`. Input tokens
beyond respective sequence lengths are masked out
automatically.
sequence_length: A 1D Tensor of shape `[batch_size]`. Memory tokens
beyond respective sequence lengths are masked out
automatically.
adjs: A 3D Tensor of shape `[batch_size, max_time, max_time]`,
containing the adjacency matrices of input sequences
encoder_output: bool. True: return encoder-like embeddings. False: return CrossGraphTransformerDecoderOutput.
mode (optional): A tensor taking value in
:tf_main:`tf.estimator.ModeKeys <estimator/ModeKeys>`,
including `TRAIN`, `EVAL`, and `PREDICT`. Used to toggle
dropout.
If `None` (default), :func:`texar.global_mode` is used.
Returns:
A Tensor of shape `[batch_size, max_time, dim]` containing the
encoded vectors.
"""
# Get adjacency masks from adjs
adj_masks = 1 - tf.cast(tf.equal(adjs, 0), dtype=tf.float32)
# Multiply input embedding with the sqrt of its dimension for
# normalization
inputs_padding = 1 - tf.sequence_mask(
sequence_length, tf.shape(inputs)[1], dtype=tf.float32)
if self._hparams.use_bert_config:
ignore_padding = attn.attention_bias_ignore_padding(
inputs_padding, bias_value=-1e4)
else:
ignore_padding = attn.attention_bias_ignore_padding(inputs_padding)
encoder_self_attention_bias = ignore_padding
input_embedding = inputs # shape (batch_size, max_time, dim)
if self._hparams.use_bert_config:
x = layers.layer_normalize(input_embedding)
x = tf.layers.dropout(x,
rate=self._hparams.embedding_dropout,
training=is_train_mode(mode))
else:
x = tf.layers.dropout(input_embedding,
rate=self._hparams.embedding_dropout,
training=is_train_mode(mode))
# Just to keep consistent with BERT, actually makes no difference
if self._hparams.use_bert_config:
pad_remover = None
else:
pad_remover = utils.transformer_utils.PadRemover(inputs_padding)
for i in range(self._hparams.num_blocks):
with tf.variable_scope("layer_{}".format(i)):
graph_multihead_attention = self.graph_multihead_attention_list[
i]
# trivial difference between BERT and original Transformer
if self._hparams.use_bert_config:
_queries_input = x
else:
_queries_input = layers.layer_normalize(x)
attention_output = graph_multihead_attention(
queries=_queries_input,
memory=memory,
adj_masks=adj_masks,
memory_attention_bias=encoder_self_attention_bias,
mode=mode,
)
attention_output = tf.layers.dropout(
attention_output,
rate=self._hparams.residual_dropout,
training=is_train_mode(mode),
)
# attention_output: weighted sum of V of memory with weights determined by querying keys of memory
x = x + attention_output
with tf.variable_scope('output'):
if self._hparams.use_bert_config:
x = layers.layer_normalize(x)
y = x
else:
y = layers.layer_normalize(x)
poswise_network = self.poswise_networks[i]
with tf.variable_scope(poswise_network.variable_scope):
original_shape = shape_list(y)
y = tf.reshape(y, [-1, self._hparams.dim])
if pad_remover:
y = tf.expand_dims(pad_remover.remove(y), axis=0)
# [1, batch_size*seq_length, hidden_dim]
layer_output = poswise_network(y, mode=mode)
sub_output = tf.layers.dropout(
layer_output,
rate=self._hparams.residual_dropout,
training=is_train_mode(mode))
if pad_remover:
sub_output = tf.reshape(pad_remover.restore(tf.squeeze(\
sub_output, axis=0)), original_shape \
)
else:
sub_output = tf.reshape(sub_output, original_shape)
x = x + sub_output
if self._hparams.use_bert_config:
x = layers.layer_normalize(x)
if not self._hparams.use_bert_config:
x = layers.layer_normalize(x)
if not self._built:
self._add_internal_trainable_variables()
self._built = True
if encoder_output:
return x
logits = self._output_layer(x)
sample_ids = tf.to_int32(tf.argmax(logits, axis=-1))
probs = ''
# probs = GumbelSoftmax(self._tau, logits=logits).sample()
# probs = tf.nn.softmax(logits / self._tau) # vanilla softmax
rets = CrossGraphTransformerFixedLengthDecoderOutput(
logits=logits, sample_id=sample_ids, probs=probs)
return rets
def _main(_):
hparams = gan_hyperparams.load_hyperparams()
train_dataset_hparams, valid_dataset_hparams, test_dataset_hparams, encoder_hparams, \
decoder_hparams, classifier_hparams, opt_hparams, loss_hparams, d_opt_hparams, args = \
hparams['train_dataset_hparams'], hparams['eval_dataset_hparams'], \
hparams['test_dataset_hparams'], hparams['encoder_hparams'], hparams['decoder_hparams'], \
hparams['classifier_hparams'], hparams['opt_hparams'], \
hparams['loss_hparams'], hparams['d_opt'], hparams['args']
# Data
train_data = tx.data.MonoTextData(train_dataset_hparams)
valid_data = tx.data.MonoTextData(valid_dataset_hparams)
test_data = tx.data.MonoTextData(test_dataset_hparams)
iterator = tx.data.FeedableDataIterator(
{'train_g': train_data, 'train_d': train_data,
'val': valid_data, 'test': test_data})
data_batch = iterator.get_next()
mask_id = train_data.vocab.token_to_id_map_py['<m>']
boa_id = train_data.vocab.token_to_id_map_py['<BOA>']
eoa_id = train_data.vocab.token_to_id_map_py['<EOA>']
eos_id = train_data.vocab.token_to_id_map_py[SpecialTokens.EOS]
pad_id = train_data.vocab.token_to_id_map_py['<PAD>']
template_pack, answer_packs = \
tx.utils.prepare_template(data_batch, args, mask_id, boa_id, eoa_id, pad_id)
gamma = tf.placeholder(dtype=tf.float32, shape=[], name='gamma')
lambda_g = tf.placeholder(dtype=tf.float32, shape=[], name='lambda_g')
# Model architecture
embedder = tx.modules.WordEmbedder(vocab_size=train_data.vocab.size,
hparams=args.word_embedding_hparams)
position_embedder = position_embedders.SinusoidsSegmentalPositionEmbedder()
encoder = tx.modules.UnidirectionalRNNEncoder(hparams=encoder_hparams)
decoder = tx.modules.BasicPositionalRNNDecoder(vocab_size=train_data.vocab.size,
hparams=decoder_hparams,
position_embedder=position_embedder)
decoder_initial_state_size = decoder.cell.state_size
connector = tx.modules.connectors.ForwardConnector(decoder_initial_state_size)
start_tokens = tf.ones_like(data_batch['length']) * boa_id
gumbel_helper = tx.modules.GumbelSoftmaxEmbeddingHelper(
embedder.embedding, start_tokens, eoa_id, gamma)
# Creates classifier
classifier = tx.modules.Conv1DClassifier(hparams=classifier_hparams)
clas_embedder = tx.modules.WordEmbedder(vocab_size=train_data.vocab.size,
hparams=args.word_embedding_hparams)
cetp_loss, d_class_loss, g_class_loss = None, None, None
cur_template_pack = template_pack
for idx, hole in enumerate(answer_packs):
template = cur_template_pack['templates']
template_word_embeds = embedder(template)
template_length = shape_list(template)[1]
channels = shape_list(template_word_embeds)[2]
template_pos_embeds = position_embedder(template_length, channels,
cur_template_pack['segment_ids'],
cur_template_pack['offsets'])
enc_input_embedded = template_word_embeds + template_pos_embeds
_, ecdr_states = encoder(
enc_input_embedded,
sequence_length=data_batch["length"])
dcdr_init_states = connector(ecdr_states)
dec_input = hole['text_ids'][:, :-1]
dec_input_word_embeds = embedder(dec_input)
decoder.set_segment_id(1)
dec_input_embedded = dec_input_word_embeds
outputs, _, _ = decoder(
initial_state=dcdr_init_states,
decoding_strategy="train_greedy",
inputs=dec_input_embedded,
sequence_length=hole["lengths"] + 1)
cur_loss = tx.utils.smoothing_cross_entropy(
outputs.logits,
hole['text_ids'][:, 1:],
train_data.vocab.size,
loss_hparams['label_confidence'],
)
cetp_loss = cur_loss if cetp_loss is None \
else tf.concat([cetp_loss, cur_loss], -1)
soft_outputs_, _, soft_length_, = decoder(
helper=gumbel_helper, initial_state=dcdr_init_states)
# Classification loss for the classifier
clas_logits, clas_preds = classifier(
inputs=clas_embedder(ids=hole['text_ids'][:, 1:]),
sequence_length=hole["lengths"]+1)
loss_d_clas = tf.nn.sigmoid_cross_entropy_with_logits(
labels=tf.to_float(tf.ones_like(data_batch['length'])), logits=clas_logits)
d_class_loss = loss_d_clas if d_class_loss is None \
else tf.concat([d_class_loss, loss_d_clas], -1)
# Classification loss for the generator, based on soft samples
soft_logits, soft_preds = classifier(
inputs=clas_embedder(soft_ids=soft_outputs_.sample_id),
sequence_length=soft_length_)
loss_g_clas = tf.nn.sigmoid_cross_entropy_with_logits(
labels=tf.to_float(tf.zeros_like(data_batch['length'])), logits=soft_logits)
g_class_loss = loss_g_clas if g_class_loss is None \
else tf.concat([g_class_loss, loss_g_clas], -1)
cur_template_pack = tx.utils.update_template_pack(cur_template_pack,
hole['text_ids'][:, 1:],
mask_id, eoa_id, pad_id)
cetp_loss = tf.reduce_mean(cetp_loss)
d_class_loss = tf.reduce_mean(d_class_loss)
g_class_loss = tf.reduce_mean(g_class_loss)
global_step = tf.Variable(0, trainable=False)
if args.learning_rate_strategy == 'static':
learning_rate = tf.Variable(1e-3, dtype=tf.float32)
elif args.learning_rate_strategy == 'dynamic':
fstep = tf.to_float(global_step)
learning_rate = opt_hparams['lr_constant'] \
* args.hidden_dim ** -0.5 \
* tf.minimum(fstep ** -0.5, fstep * opt_hparams['warmup_steps'] ** -1.5)
else:
raise ValueError('Unknown learning_rate_strategy: %s, expecting one of '
'[\'static\', \'dynamic\']' % args.learning_rate_strategy)
g_loss = cetp_loss + lambda_g * g_class_loss
g_vars = tx.utils.collect_trainable_variables(
[embedder, encoder, connector, decoder])
optimizer = tf.train.AdamOptimizer(
learning_rate=learning_rate,
beta1=opt_hparams['Adam_beta1'],
beta2=opt_hparams['Adam_beta2'],
epsilon=opt_hparams['Adam_epsilon'],
)
train_op = optimizer.minimize(g_loss, global_step, var_list=g_vars)
d_loss = d_class_loss
d_vars = tx.utils.collect_trainable_variables([clas_embedder, classifier])
train_op_d = tx.core.get_train_op(d_loss, d_vars, hparams=d_opt_hparams)
# Inference
predictions = []
cur_test_pack = template_pack
for idx, hole in enumerate(answer_packs):
template = cur_test_pack['templates']
template_word_embeds = embedder(template)
template_length = shape_list(template)[1]
channels = shape_list(template_word_embeds)[2]
template_pos_embeds = position_embedder(template_length, channels,
cur_test_pack['segment_ids'],
cur_test_pack['offsets'])
enc_input_embedded = template_word_embeds + template_pos_embeds
_, ecdr_states = encoder(
enc_input_embedded,
sequence_length=data_batch["length"])
dcdr_init_states = connector(ecdr_states)
decoder.set_segment_id(1)
outputs_infer, _, _ = decoder(
decoding_strategy="infer_positional",
start_tokens=start_tokens,
end_token=eoa_id,
embedding=embedder,
initial_state=dcdr_init_states)
predictions.append(outputs_infer.sample_id)
cur_test_pack = tx.utils.update_template_pack(cur_test_pack,
outputs_infer.sample_id,
mask_id, eoa_id, pad_id)
eval_saver = tf.train.Saver(max_to_keep=5)
def _train_epochs(session, cur_epoch, gamma_, lambda_g_):
loss_lists, ppl_lists = [], []
while True:
try:
fetches_d = {
'train_op_d': train_op_d,
'd_loss': d_loss
}
feed_d = {
iterator.handle: iterator.get_handle(sess, 'train_d'),
gamma: gamma_,
lambda_g: lambda_g_,
tx.context.global_mode(): tf.estimator.ModeKeys.TRAIN
}
rtns_d = session.run(fetches_d, feed_dict=feed_d)
d_loss_ = rtns_d['d_loss']
fetches_g = {
'template': template_pack,
'holes': answer_packs,
'train_op': train_op,
'step': global_step,
'lr': learning_rate,
'loss': cetp_loss,
'g_loss': g_loss
}
feed_g = {
iterator.handle: iterator.get_handle(sess, 'train_g'),
gamma: gamma_,
lambda_g: lambda_g_,
tx.context.global_mode(): tf.estimator.ModeKeys.TRAIN
}
rtns = session.run(fetches_g, feed_dict=feed_g)
step, template_, holes_, cetp_loss_, g_loss_ = \
rtns['step'], rtns['template'], rtns['holes'], rtns['loss'], rtns['g_loss']
ppl = np.exp(cetp_loss_)
if step % 200 == 1:
rst = 'step:%s source:%s g_loss:%f d_loss:%f ppl:%f lr:%f' % \
(step, template_['text_ids'].shape, g_loss_, d_loss_, ppl, rtns['lr'])
print(rst)
loss_lists.append(g_loss_)
ppl_lists.append(ppl)
except tf.errors.OutOfRangeError:
break
return loss_lists[::50], ppl_lists[::50]
def _test_epoch(cur_sess, cur_epoch, gamma_, lambda_g_, mode='test'):
def _id2word_map(id_arrays):
return [' '.join([train_data.vocab._id_to_token_map_py[i]
for i in sent]) for sent in id_arrays]
templates_list, targets_list, hypothesis_list = [], [], []
cnt = 0
loss_lists, ppl_lists = [], []
while True:
try:
fetches = {
'data_batch': data_batch,
'predictions': predictions,
'template': template_pack,
'step': global_step,
'loss': cetp_loss
}
feed = {
iterator.handle: iterator.get_handle(sess, mode),
gamma: gamma_,
lambda_g: lambda_g_,
tx.context.global_mode(): tf.estimator.ModeKeys.EVAL
}
rtns = cur_sess.run(fetches, feed_dict=feed)
real_templates_, templates_, targets_, predictions_ = \
rtns['template']['templates'], rtns['template']['text_ids'], \
rtns['data_batch']['text_ids'], rtns['predictions']
loss = rtns['loss']
ppl = np.exp(loss)
loss_lists.append(loss)
ppl_lists.append(ppl)
filled_templates = \
tx.utils.fill_template(template_pack=rtns['template'],
predictions=rtns['predictions'],
eoa_id=eoa_id, pad_id=pad_id, eos_id=eos_id)
templates, targets, generateds = _id2word_map(real_templates_.tolist()), \
_id2word_map(targets_), \
_id2word_map(filled_templates)
for template, target, generated in zip(templates, targets, generateds):
template = template.split('<EOS>')[0].split('<PAD>')[0].strip().split()
target = target.split('<EOS>')[0].split('<PAD>')[0].strip().split()
got = generated.split('<EOS>')[0].split('<PAD>')[0].strip().split()
templates_list.append(template)
targets_list.append(target)
hypothesis_list.append(got)
cnt += 1
if mode is not 'test' and cnt >= 60:
break
except tf.errors.OutOfRangeError:
break
avg_loss, avg_ppl = np.mean(loss_lists), np.mean(ppl_lists)
outputs_tmp_filename = args.log_dir + 'epoch{}.beam{}.outputs.tmp'. \
format(cur_epoch, args.beam_width)
template_tmp_filename = args.log_dir + 'epoch{}.beam{}.templates.tmp'. \
format(cur_epoch, args.beam_width)
refer_tmp_filename = os.path.join(args.log_dir, 'eval_reference.tmp')
with codecs.open(outputs_tmp_filename, 'w+', 'utf-8') as tmpfile, \
codecs.open(template_tmp_filename, 'w+', 'utf-8') as tmptpltfile, \
codecs.open(refer_tmp_filename, 'w+', 'utf-8') as tmpreffile:
for hyp, tplt, tgt in zip(hypothesis_list, templates_list, targets_list):
tmpfile.write(' '.join(hyp) + '\n')
tmptpltfile.write(' '.join(tplt) + '\n')
tmpreffile.write(' '.join(tgt) + '\n')
eval_bleu = float(100 * bleu_tool.bleu_wrapper(
refer_tmp_filename, outputs_tmp_filename, case_sensitive=True))
template_bleu = float(100 * bleu_tool.bleu_wrapper(
refer_tmp_filename, template_tmp_filename, case_sensitive=True))
print('epoch:{} {}_bleu:{} template_bleu:{} {}_loss:{} {}_ppl:{} '.
format(cur_epoch, mode, eval_bleu, template_bleu, mode, avg_loss, mode, avg_ppl))
os.remove(outputs_tmp_filename)
os.remove(template_tmp_filename)
os.remove(refer_tmp_filename)
if args.save_eval_output:
result_filename = \
args.log_dir + 'epoch{}.beam{}.{}.results.bleu{:.3f}' \
.format(cur_epoch, args.beam_width, mode, eval_bleu)
with codecs.open(result_filename, 'w+', 'utf-8') as resultfile:
for tmplt, tgt, hyp in zip(templates_list, targets_list, hypothesis_list):
resultfile.write("- template: " + ' '.join(tmplt) + '\n')
resultfile.write("- expected: " + ' '.join(tgt) + '\n')
resultfile.write('- got: ' + ' '.join(hyp) + '\n\n')
return {
'eval': eval_bleu,
'template': template_bleu
}, avg_ppl
def _draw_train_loss(epoch, loss_list, mode):
plt.figure(figsize=(14, 10))
plt.plot(loss_list, '--', linewidth=1, label='loss trend')
plt.ylabel('%s till epoch %s' % (mode, epoch))
plt.xlabel('every 50 steps, present_rate=%f' % args.present_rate)
plt.savefig(args.log_dir + '/img/%s_curve.png' % mode)
plt.close('all')
def _draw_bleu(epoch, test_bleu, tplt_bleu, train_bleu, train_tplt_bleu):
plt.figure(figsize=(14, 10))
legends = []
plt.plot(test_bleu, '--', linewidth=1, label='test bleu')
plt.plot(tplt_bleu, '--', linewidth=1, label='template bleu')
legends.extend(['test bleu', 'template bleu'])
plt.ylabel('bleu till epoch {}'.format(epoch))
plt.xlabel('every epoch')
plt.legend(legends, loc='upper left')
plt.savefig(args.log_dir + '/img/bleu.png')
plt.figure(figsize=(14, 10))
legends = []
plt.plot(train_bleu, '--', linewidth=1, label='train bleu')
plt.plot(train_tplt_bleu, '--', linewidth=1, label='train template bleu')
legends.extend(['train bleu', 'train template bleu'])
plt.ylabel('bleu till epoch {}'.format(epoch))
plt.xlabel('every epoch')
plt.legend(legends, loc='upper left')
plt.savefig(args.log_dir + '/img/train_bleu.png')
plt.close('all')
config_ = tf.ConfigProto(allow_soft_placement=True)
config_.gpu_options.allow_growth = True
with tf.Session(config=config_) as sess:
sess.run(tf.global_variables_initializer())
sess.run(tf.local_variables_initializer())
sess.run(tf.tables_initializer())
iterator.initialize_dataset(sess)
loss_list, ppl_list, test_ppl_list = [], [], []
test_bleu, tplt_bleu, train_bleu, train_tplt_bleu = [], [], [], []
gamma_, lambda_g_ = 1., 0.
if args.running_mode == 'train_and_evaluate':
for epoch in range(70, args.max_train_epoch):
# Anneals the gumbel-softmax temperature
if epoch > args.pretrain_epoch:
gamma_ = max(0.001, gamma_ * args.gamma_decay)
lambda_g_ = args.lambda_g
# bleu on test set and train set
if epoch % args.bleu_interval == 0 or epoch == args.max_train_epoch - 1:
iterator.restart_dataset(sess, 'test')
bleu_scores, test_ppl = _test_epoch(sess, epoch, gamma_, lambda_g_)
test_bleu.append(bleu_scores['eval'])
tplt_bleu.append(bleu_scores['template'])
test_ppl_list.append(test_ppl)
_draw_train_loss(epoch, test_ppl_list, mode='test_perplexity')
iterator.restart_dataset(sess, 'train_g')
train_bleu_scores, _ = _test_epoch(sess, epoch, gamma_, lambda_g_, mode='train_g')
train_bleu.append(train_bleu_scores['eval'])
train_tplt_bleu.append(train_bleu_scores['template'])
_draw_bleu(epoch, test_bleu, tplt_bleu, train_bleu, train_tplt_bleu)
eval_saver.save(sess, args.log_dir + 'my-model-latest.ckpt')
# train
iterator.restart_dataset(sess, ['train_g', 'train_d'])
losses, ppls = _train_epochs(sess, epoch, gamma_, lambda_g_)
loss_list.extend(losses)
ppl_list.extend(ppls)
_draw_train_loss(epoch, loss_list, mode='train_loss')
_draw_train_loss(epoch, ppl_list, mode='perplexity')
sys.stdout.flush()
if epoch == args.pretrain_epoch:
eval_saver.save(sess, args.log_dir + 'pretrained-model.ckpt')
def _build(
self, # pylint: disable=arguments-differ
memory=None,
memory_sequence_length=None,
memory_attention_bias=None,
inputs=None,
sequence_length=None,
decoding_strategy='train_greedy',
beam_width=None,
length_penalty=0.,
start_tokens=None,
end_token=None,
context=None,
context_sequence_length=None,
softmax_temperature=None,
max_decoding_length=None,
impute_finished=False,
helper=None,
mode=None):
"""Performs decoding.
The interface is very similar to that of RNN decoders
(:meth:`texar.modules.RNNDecoderBase._build`). In particular,
the function provides **3 ways** to specify the decoding method, with
varying flexibility:
1. The :attr:`decoding_strategy` argument.
- **"train_greedy"**: decoding in teacher-forcing fashion (i.e.,
feeding ground truth to decode the next step), and for each step
sample is obtained by taking the `argmax` of logits.
Argument :attr:`inputs` is required for this strategy.
:attr:`sequence_length` is optional.
- **"infer_greedy"**: decoding in inference fashion (i.e., feeding
`generated` sample to decode the next step), and for each step
sample is obtained by taking the `argmax` of logits.
Arguments :attr:`(start_tokens, end_token)` are
required for this strategy, and argument
:attr:`max_decoding_length` is optional.
- **"infer_sample"**: decoding in inference fashion, and for each
step sample is obtained by `random sampling` from the logits.
Arguments :attr:`(start_tokens, end_token)` are required for this
strategy, and argument :attr:`max_decoding_length` is optional.
This argument is used only when arguments :attr:`helper` and
:attr:`beam_width` are both `None`.
2. The :attr:`helper` argument: An instance of subclass of
:tf_main:`tf.contrib.seq2seq.Helper <contrib/seq2seq/Helper>`.
This provides a superset of decoding strategies than above.
The interface is the same as in RNN decoders.
Please refer to :meth:`texar.modules.RNNDecoderBase._build` for
detailed usage and examples.
Note that, here, though using a :tf_main:`TrainingHelper
<contrib/seq2seq/TrainingHelper>` corresponding to the
"train_greedy" strategy above, the implementation is *slower* than
directly setting `decoding_strategy="train_greedy"` (though the
output results are the same).
Argument :attr:`max_decoding_length` is optional.
3. **Beam search**: set :attr:`beam_width` to use beam search decoding.
Arguments :attr:`(start_tokens, end_token)` are required,
and argument :attr:`max_decoding_length` is optional.
Args:
memory (optional): The memory to attend, e.g., the output of an RNN encoder.
A Tensor of shape `[batch_size, memory_max_time, dim]`.
memory_sequence_length (optional): A Tensor of shape `[batch_size]`
containing the sequence lengths for the batch entries in
memory. Used to create attention bias of
:attr:`memory_attention_bias` is not given. Ignored if
`memory_attention_bias` is provided.
memory_attention_bias (optional): A Tensor of shape
`[batch_size, num_heads, memory_max_time, dim]`.
An attention bias typically sets the value of a padding
position to a large negative value for masking. If not given,
:attr:`memory_sequence_length` is used to automatically
create an attention bias.
inputs (optional): Input tensor for teacher forcing decoding, of
shape `[batch_size, target_max_time, emb_dim]` containing the
target sequence word embeddings.
Used when :attr:`decoding_strategy` is set to "train_greedy".
sequence_length (optional): A Tensor of shape `[batch_size]`,
containing the sequence length of :attr:`inputs`.
Tokens beyond the respective sequence length are masked out.
Used when :attr:`decoding_strategy` is set to
"train_greedy".
decoding_strategy (str): A string specifying the decoding
strategy, including "train_greedy", "infer_greedy",
"infer_sample".
Different arguments are required based on the
strategy. See above for details. Ignored if
:attr:`beam_width` or :attr:`helper` is set.
beam_width (int): Set to use beam search. If given,
:attr:`decoding_strategy` is ignored.
length_penalty (float): Length penalty coefficient used in beam search
decoding. Refer to https://arxiv.org/abs/1609.08144
for more details.
It Should be larger if longer sentences are wanted.
start_tokens (optional): An int Tensor of shape `[batch_size]`,
containing the start tokens.
Used when :attr:`decoding_strategy` = "infer_greedy" or
"infer_sample", or :attr:`beam_width` is set.
Ignored when context is set.
end_token (optional): An int 0D Tensor, the token that marks end
of decoding.
Used when :attr:`decoding_strategy` = "infer_greedy" or
"infer_sample", or :attr:`beam_width` is set.
context (optional): An int Tensor of shape `[batch_size, length]`,
containing the starting tokens for decoding.
If context is set, the start_tokens will be ignored.
context_sequence_length (optional): specify the length of context.
softmax_temperature (optional): A float 0D Tensor, value to divide
the logits by before computing the softmax. Larger values
(above 1.0) result in more random samples. Must > 0. If `None`,
1.0 is used.
Used when :attr:`decoding_strategy` = "infer_sample"`.
max_decoding_length (optional): An int scalar Tensor indicating
the maximum allowed number of decoding steps.
If `None` (default), use "max_decoding_length" defined in
:attr:`hparams`. Ignored in "train_greedy" decoding.
impute_finished (bool): If `True`, then states for batch
entries which are marked as finished get copied through and
the corresponding outputs get zeroed out. This causes some
slowdown at each time step, but ensures that the final state
and outputs have the correct values and that backprop ignores
time steps that were marked as finished. Ignored in
"train_greedy" decoding.
helper (optional): An instance of
:tf_main:`Helper <contrib/seq2seq/Helper>` that defines the
decoding strategy. If given, :attr:`decoding_strategy` is
ignored.
mode (optional): A tensor taking value in
:tf_main:`tf.estimator.ModeKeys <estimator/ModeKeys>`, including
`TRAIN`, `EVAL`, and `PREDICT`. Controls dropout mode.
If `None` (default), :func:`texar.global_mode`
is used.
Returns:
- For **"train_greedy"** decoding, returns an instance of \
:class:`~texar.modules.TransformerDecoderOutput` which contains\
`sample_id` and `logits`.
- For **"infer_greedy"** and **"infer_sample"** decoding or\
decoding with :attr:`helper`, returns\
a tuple `(outputs, sequence_lengths)`, where `outputs` is an \
instance of :class:`~texar.modules.TransformerDecoderOutput` as\
in "train_greedy", and `sequence_lengths` is a Tensor of shape\
`[batch_size]` containing the length of each sample.
- For **beam search** decoding, returns a `dict` containing keys\
"sample_id" and "log_prob".
- **"sample_id"** is an int Tensor of shape \
`[batch_size, max_time, beam_width]` containing generated\
token indexes. `sample_id[:,:,0]` is the highest-probable \
sample.
- **"log_prob"** is a float Tensor of shape \
`[batch_size, beam_width]` containing the log probability \
of each sequence sample.
"""
if memory is not None:
if memory_attention_bias is None:
if memory_sequence_length is None:
raise ValueError("`memory_sequence_length` is required if "
"`memory_attention_bias` is not given.")
enc_padding = 1 - tf.sequence_mask(memory_sequence_length,
tf.shape(memory)[1],
dtype=tf.float32)
memory_attention_bias = attn.attention_bias_ignore_padding(
enc_padding)
# record the context, which will be used in step function
# for dynamic_decode
if context is not None:
start_tokens = context[:, 0]
self.context = context[:, 1:]
self.context_sequence_length = context_sequence_length - 1
else:
self.context = None
if helper is None and beam_width is None and \
decoding_strategy == 'train_greedy': # Teacher-forcing
if sequence_length is not None:
inputs = mask_sequences(inputs, sequence_length, tensor_rank=3)
decoder_self_attention_bias = (attn.attention_bias_lower_triangle(
shape_list(inputs)[1]))
if self._hparams.scale_embeds:
target_inputs = inputs * self._hparams.dim**0.5
else:
target_inputs = inputs
_, lengths, _ = shape_list(target_inputs)
positions = tf.expand_dims(tf.range(lengths, dtype=tf.int32), 0)
pos_embeds = self.position_embedder(positions)
inputs = target_inputs + pos_embeds
decoder_output = self._self_attention_stack(
inputs,
memory,
decoder_self_attention_bias=decoder_self_attention_bias,
memory_attention_bias=memory_attention_bias,
cache=None,
mode=mode)
logits = self.output_layer(decoder_output)
preds = tf.to_int32(tf.argmax(logits, axis=-1))
rets = TransformerDecoderOutput(logits=logits, sample_id=preds)
else:
if max_decoding_length is None:
max_decoding_length = self._hparams.max_decoding_length
self._inputs_to_outputs = self._inputs_to_outputs_fn(
max_decoding_length + 1)
if beam_width is None: #Inference-like decoding
# Prepare helper
if helper is not None:
# ignore `decoding_strategy`
pass
else:
if decoding_strategy == "infer_greedy":
helper = tf.contrib.seq2seq.GreedyEmbeddingHelper(
self._embedding, start_tokens, end_token)
elif decoding_strategy == "infer_sample":
helper = tf.contrib.seq2seq.SampleEmbeddingHelper(
self._embedding, start_tokens, end_token,
softmax_temperature)
else:
raise ValueError(
"Unknown decoding strategy: {}".format(
decoding_strategy))
self._helper = helper
self._cache = self._init_cache(memory,
memory_attention_bias,
beam_search_decoding=False)
if context is not None:
self.context = tf.pad(
self.context,
[[0, 0],
[0, max_decoding_length - tf.shape(self.context)[1]]])
outputs, cache, sequence_lengths = dynamic_decode(
decoder=self,
impute_finished=impute_finished,
maximum_iterations=max_decoding_length,
output_time_major=False,
scope=self.variable_scope)
if context is not None:
# Here the length of sample_id will be larger than that
# of logit by 1, because there will be a additional
# start_token in the returned sample_id.
# the start_id should be the first token of the
# given context
outputs = TransformerDecoderOutput(
logits=outputs.logits,
sample_id=tf.concat([
tf.expand_dims(start_tokens, 1), outputs.sample_id
],
axis=1))
sequence_lengths = sequence_lengths + 1
rets = outputs, sequence_lengths
else: #Beam-search decoding
# ignore `decoding_strategy`
# assume `helper` is not set
if helper is not None:
raise ValueError("Must not set 'beam_width' and 'helper' "
"simultaneously.")
_batch_size = tf.shape(start_tokens)[0]
self._cache = self._init_cache(memory,
memory_attention_bias,
beam_search_decoding=True,
batch_size=_batch_size)
# The output format is different when running beam search
sample_id, log_prob = self._beam_decode(
start_tokens,
end_token,
beam_width=beam_width,
length_penalty=length_penalty,
decode_length=max_decoding_length,
)
rets = {'sample_id': sample_id, 'log_prob': log_prob}
if not self._built:
self._add_internal_trainable_variables()
self._built = True
return rets
def beam_search(symbols_to_logits_fn,
initial_ids,
beam_size,
decode_length,
vocab_size,
alpha,
eos_id,
states=None,
stop_early=True):
"""Beam search with length penalties.
Requires a function that can take the currently decoded sybmols and
return the logits for the next symbol. The implementation is inspired
by https://arxiv.org/abs/1609.08144.
When running, the beam search steps can be visualized by using tfdbg to
watch the operations generating the output ids for each beam step.
These operations have the pattern:
(alive|finished)_topk_(seq,scores)
Operations marked `alive` represent the new beam sequences that will be
processed in the next step. Operations marked `finished` represent
the completed beam sequences, which may be padded with 0s if no beams
finished.
Operations marked `seq` store the full beam sequence for the time step.
Operations marked `scores` store the sequence's final log scores.
The beam search steps will be processed sequentially in order, so when
capturing observed from these operations, tensors, clients can make
assumptions about which step is being recorded.
WARNING: Assumes 2nd dimension of tensors in `states` and not
invariant, this means that the shape of the 2nd dimension of these
tensors will not be available (i.e. set to None) inside
symbols_to_logits_fn.
Args:
symbols_to_logits_fn: Interface to the model, to provide logits.
Should take [batch_size, decoded_ids] and return
[batch_size, vocab_size]
initial_ids: Ids to start off the decoding, this will be the first
thing handed to symbols_to_logits_fn (after expanding to beam size)
[batch_size]
beam_size: Size of the beam.
decode_length: Number of steps to decode for.
vocab_size: Size of the vocab, must equal the size of the logits
returned by symbols_to_logits_fn
alpha: alpha for length penalty.
states: dict (possibly nested) of decoding states.
eos_id: ID for end of sentence.
stop_early: a boolean - stop once best sequence is provably
determined.
Returns:
Tuple of
(decoded beams [batch_size, beam_size, decode_length]
decoding probablities [batch_size, beam_size])
"""
batch_size = shape_list(initial_ids)[0]
# Assume initial_ids are prob 1.0
initial_log_probs = tf.constant([[0.] + [-float("inf")] * (beam_size - 1)])
# Expand to beam_size (batch_size, beam_size)
alive_log_probs = tf.tile(initial_log_probs, [batch_size, 1])
# Expand each batch and state to beam_size
alive_seq = _expand_to_beam_size(initial_ids, beam_size)
alive_seq = tf.expand_dims(alive_seq, axis=2)
#(batch_size, beam_size, 1)
if states:
states = nest.map_structure(
lambda state: _expand_to_beam_size(state, beam_size), states)
else:
states = {}
# Finished will keep track of all the sequences that have finished so
# far
# Finished log probs will be negative infinity in the beginning
# finished_flags will keep track of booleans
finished_seq = tf.zeros(shape_list(alive_seq), tf.int32)
# Setting the scores of the initial to negative infinity.
finished_scores = tf.ones([batch_size, beam_size]) * -INF
finished_flags = tf.zeros([batch_size, beam_size], tf.bool)
def grow_finished(finished_seq, finished_scores, finished_flags, curr_seq,
curr_scores, curr_finished):
"""Given sequences and scores, will gather the top k=beam size
sequences.
Args:
finished_seq: Current finished sequences.
[batch_size, beam_size, current_decoded_length]
finished_scores: scores for each of these sequences.
[batch_size, beam_size]
finished_flags: finished bools for each of these sequences.
[batch_size, beam_size]
curr_seq: current topk sequence that has been grown by one
position.
[batch_size, beam_size, current_decoded_length]
curr_scores: scores for each of these sequences. [batch_size,
beam_size]
curr_finished: Finished flags for each of these sequences.
[batch_size, beam_size]
Returns:
Tuple of
(Topk sequences based on scores,
log probs of these sequences,
Finished flags of these sequences)
"""
# First append a column of 0'ids to finished to make the same
# length with finished scores
finished_seq = tf.concat(
[finished_seq,
tf.zeros([batch_size, beam_size, 1], tf.int32)],
axis=2)
# Set the scores of the unfinished seq in curr_seq to large
# negative values
curr_scores += (1. - tf.to_float(curr_finished)) * -INF
# concatenating the sequences and scores along beam axis
curr_finished_seq = tf.concat([finished_seq, curr_seq], axis=1)
curr_finished_scores = tf.concat([finished_scores, curr_scores],
axis=1)
curr_finished_flags = tf.concat([finished_flags, curr_finished],
axis=1)
return compute_topk_scores_and_seq(curr_finished_seq,
curr_finished_scores,
curr_finished_scores,
curr_finished_flags, beam_size,
batch_size, "grow_finished")
def grow_alive(curr_seq, curr_scores, curr_log_probs, curr_finished,
states):
"""Given sequences and scores, will gather the top k=beam size
sequences.
Args:
curr_seq: current topk sequence that has been grown by one
position.
[batch_size, beam_size, i+1]
curr_scores: scores for each of these sequences. [batch_size,
beam_size]
curr_log_probs: log probs for each of these sequences.
[batch_size, beam_size]
curr_finished: Finished flags for each of these sequences.
[batch_size, beam_size]
states: dict (possibly nested) of decoding states.
Returns:
Tuple of
(Topk sequences based on scores,
log probs of these sequences,
Finished flags of these sequences)
"""
# Set the scores of the finished seq in curr_seq to large negative
# values
curr_scores += tf.to_float(curr_finished) * -INF
return compute_topk_scores_and_seq(curr_seq, curr_scores,
curr_log_probs, curr_finished,
beam_size, batch_size, "grow_alive",
states)
def grow_topk(i, alive_seq, alive_log_probs, states):
r"""Inner beam seach loop.
This function takes the current alive sequences, and grows them to
topk sequences where k = 2*beam. We use 2*beam because, we could
have beam_size number of sequences that might hit <EOS> and there
will be no alive sequences to continue. With 2*beam_size, this
will not happen. This relies on the assumption the vocab size is >
beam size. If this is true, we'll have at least beam_size non
<EOS> extensions if we extract the next top 2*beam words.
Length penalty is given by = (5+len(decode)/6) ^ -\alpha.
Pls refer to https://arxiv.org/abs/1609.08144.
Args:
i: loop index
alive_seq: Topk sequences decoded so far [batch_size,
beam_size, i+1]
alive_log_probs: probabilities of these sequences.
[batch_size, beam_size]
states: dict (possibly nested) of decoding states.
Returns:
Tuple of
(Topk sequences extended by the next word,
The log probs of these sequences,
The scores with length penalty of these sequences,
Flags indicating which of these sequences have finished
decoding, dict of transformed decoding states)
"""
# Get the logits for all the possible next symbols
flat_ids = tf.reshape(alive_seq, [batch_size * beam_size, -1])
# (batch_size * beam_size, decoded_length)
if states:
flat_states = nest.map_structure(_merge_beam_dim, states)
flat_logits, flat_states = symbols_to_logits_fn(
flat_ids, i, flat_states)
states = nest.map_structure(
lambda t: _unmerge_beam_dim(t, batch_size, beam_size),
flat_states)
else:
flat_logits = symbols_to_logits_fn(flat_ids)
logits = tf.reshape(flat_logits, [batch_size, beam_size, -1])
# Convert logits to normalized log probs
candidate_log_probs = log_prob_from_logits(logits)
# Multiply the probabilites by the current probabilites of the
# beam.
# (batch_size, beam_size, vocab_size) + (batch_size, beam_size, 1)
log_probs = candidate_log_probs + tf.expand_dims(alive_log_probs,
axis=2)
length_penalty = tf.pow(((5. + tf.to_float(i + 1)) / 6.), alpha)
curr_scores = log_probs / length_penalty
# Flatten out (beam_size, vocab_size) probs in to a list of
# possibilites
flat_curr_scores = tf.reshape(curr_scores,
[-1, beam_size * vocab_size])
topk_scores, topk_ids = tf.nn.top_k(flat_curr_scores, k=beam_size * 2)
# Recovering the log probs because we will need to send them back
topk_log_probs = topk_scores * length_penalty
# Work out what beam the top probs are in.
topk_beam_index = topk_ids // vocab_size
topk_ids %= vocab_size # Unflatten the ids
# The next three steps are to create coordinates for tf.gather_nd
# to pull out the correct seqences from id's that we need to grow.
# We will also use the coordinates to gather the booleans of the
# beam items that survived.
batch_pos = compute_batch_indices(batch_size, beam_size * 2)
# top beams will give us the actual coordinates to do the gather.
# stacking will create a tensor of dimension batch * beam * 2,
# where the last dimension contains the i,j gathering coordinates.
topk_coordinates = tf.stack([batch_pos, topk_beam_index], axis=2)
# Gather up the most probable 2*beams both for the ids and
# finished_in_alive bools
topk_seq = tf.gather_nd(alive_seq, topk_coordinates)
if states:
states = nest.map_structure(
lambda state: tf.gather_nd(state, topk_coordinates), states)
# Append the most probable alive
topk_seq = tf.concat(
[topk_seq, tf.expand_dims(topk_ids, axis=2)], axis=2)
topk_finished = tf.equal(topk_ids, eos_id)
return topk_seq, topk_log_probs, topk_scores, topk_finished, states
def inner_loop(i, alive_seq, alive_log_probs, finished_seq,
finished_scores, finished_flags, states):
"""Inner beam seach loop.
There are three groups of tensors, alive, finished, and topk.
The alive group contains information about the current alive
sequences. The topk group contains information about alive + topk
current decoded words the finished group contains information
about finished sentences, that is, the ones that have decoded to
<EOS>. These are what we return.
The general beam search algorithm is as follows:
While we haven't terminated (pls look at termination condition)
1. Grow the current alive to get beam*2 topk sequences
2. Among the topk, keep the top beam_size ones that haven't
reached EOS into alive
3. Among the topk, keep the top beam_size ones have reached
EOS into finished
Repeat
To make things simple with using fixed size tensors, we will end
up inserting unfinished sequences into finished in the beginning.
To stop that we add -ve INF to the score of the unfinished
sequence so that when a true finished sequence does appear, it
will have a higher score than all the unfinished ones.
Args:
i: loop index
alive_seq: Topk sequences decoded so far [batch_size,
beam_size, i+1]
alive_log_probs: probabilities of the beams. [batch_size,
beam_size]
finished_seq: Current finished sequences.
[batch_size, beam_size, i+1]
finished_scores: scores for each of these sequences.
[batch_size, beam_size]
finished_flags: finished bools for each of these sequences.
[batch_size, beam_size]
states: dict (possibly nested) of decoding states.
Returns:
Tuple of
(Incremented loop index
New alive sequences,
Log probs of the alive sequences,
New finished sequences,
Scores of the new finished sequences,
Flags inidicating which sequence in finished as reached
EOS,
dict of final decoding states)
"""
# Each inner loop, we carry out three steps:
# 1. Get the current topk items.
# 2. Extract the ones that have finished and haven't finished
# 3. Recompute the contents of finished based on scores.
topk_seq, topk_log_probs, topk_scores, topk_finished, states =\
grow_topk(i, alive_seq, alive_log_probs, states)
alive_seq, alive_log_probs, _, states = grow_alive(
topk_seq, topk_scores, topk_log_probs, topk_finished, states)
finished_seq, finished_scores, finished_flags, _ = grow_finished(
finished_seq, finished_scores, finished_flags, topk_seq,
topk_scores, topk_finished)
return (i + 1, alive_seq, alive_log_probs, finished_seq,
finished_scores, finished_flags, states)
def _is_finished(i, unused_alive_seq, alive_log_probs, unused_finished_seq,
finished_scores, finished_in_finished, unused_states):
"""Checking termination condition.
We terminate when we decoded up to decode_length or the lowest
scoring item in finished has a greater score that the higest prob
item in alive divided by the max length penalty
Args:
i: loop index
alive_log_probs: probabilities of the beams. [batch_size,
beam_size]
finished_scores: scores for each of these sequences.
[batch_size, beam_size]
finished_in_finished: finished bools for each of these
sequences. [batch_size, beam_size]
Returns:
Bool.
"""
if not stop_early:
return tf.less(i, decode_length)
max_length_penalty = tf.pow(((5. + tf.to_float(decode_length)) \
/ 6.), alpha)
# The best possible score of the most likley alive sequence
lower_bound_alive_scores = alive_log_probs[:, 0] /\
max_length_penalty
# Now to compute the lowest score of a finished sequence in
# finished
# If the sequence isn't finished, we multiply it's score by 0.
# since scores are all -ve, taking the min will give us the score
# of the lowest finished item.
lowest_score_of_fininshed_in_finished = tf.reduce_min(
finished_scores * tf.to_float(finished_in_finished), axis=1)
# If none of the sequences have finished, then the min will be 0
# and we have to replace it by -ve INF if it is. The score of any
# seq in alive will be much higher than -ve INF and the
# termination condition will not be met.
lowest_score_of_fininshed_in_finished += (
(1. - tf.to_float(tf.reduce_any(finished_in_finished, 1))) * -INF)
bound_is_met = tf.reduce_all(
tf.greater(lowest_score_of_fininshed_in_finished,
lower_bound_alive_scores))
return tf.logical_and(tf.less(i, decode_length),
tf.logical_not(bound_is_met))
(_, alive_seq, alive_log_probs, finished_seq, finished_scores,
finished_flags, _) = tf.while_loop(
_is_finished,
inner_loop, [
tf.constant(0), alive_seq, alive_log_probs, finished_seq,
finished_scores, finished_flags, states
],
shape_invariants=[
tf.TensorShape([]),
tf.TensorShape([None, None, None]),
alive_log_probs.get_shape(),
tf.TensorShape([None, None, None]),
finished_scores.get_shape(),
finished_flags.get_shape(),
nest.map_structure(get_state_shape_invariants, states),
],
parallel_iterations=1,
back_prop=False)
alive_seq.set_shape((None, beam_size, None))
finished_seq.set_shape((None, beam_size, None))
# Accounting for corner case: It's possible that no sequence in alive
# for a particular batch item ever reached EOS. In that case, we
# should just copy the contents of alive for that batch item. tf
# reduce_any(finished_flags, 1)
# if 0, means that no sequence for that batch index had reached EOS.
# We need to do the same for the scores as well.
finished_seq = tf.where(tf.reduce_any(finished_flags, 1), finished_seq,
alive_seq)
finished_scores = tf.where(tf.reduce_any(finished_flags, 1),
finished_scores, alive_log_probs)
return finished_seq, finished_scores
