def encode(self, inputs, attention_bias):
"""Generate continuous representation for inputs.
Args:
inputs: int tensor with shape [batch_size, input_length].
attention_bias: float tensor with shape [batch_size, 1, 1, input_length]
Returns:
float tensor with shape [batch_size, input_length, hidden_size]
"""
with tf.name_scope("encode"):
# Prepare inputs to the layer stack by adding positional encodings and
# applying dropout.
embedded_inputs = self.embedding_softmax_layer(inputs)
inputs_padding = model_utils.get_padding(inputs)
with tf.name_scope("add_pos_encoding"):
length = tf.shape(embedded_inputs)[1]
pos_encoding = model_utils.get_position_encoding(
length, self.params["hidden_size"])
encoder_inputs = embedded_inputs + pos_encoding
if self.train:
encoder_inputs = tf.nn.dropout(
encoder_inputs,
1 - self.params["layer_postprocess_dropout"])
return self.encoder_stack(encoder_inputs, attention_bias,
inputs_padding)
def _get_symbols_to_logits_fn(self, max_decode_length):
"""Returns a decoding function that calculates logits of the next tokens."""
timing_signal = model_utils.get_position_encoding(
max_decode_length + 1, self.params["hidden_size"])
decoder_self_attention_bias = model_utils.get_decoder_self_attention_bias(
max_decode_length)
def symbols_to_logits_fn(ids, i, cache):
"""Generate logits for next potential IDs.
Args:
ids: Current decoded sequences.
int tensor with shape [batch_size * beam_size, i + 1]
i: Loop index
cache: dictionary of values storing the encoder output, encoder-decoder
attention bias, and previous decoder attention values.
Returns:
Tuple of
(logits with shape [batch_size * beam_size, vocab_size],
updated cache values)
"""
# Set decoder input to the last generated IDs
decoder_input = ids[:, -1:]
# Preprocess decoder input by getting embeddings and adding timing signal.
decoder_input = self.embedding_softmax_layer(decoder_input)
decoder_input += timing_signal[i:i + 1]
self_attention_bias = decoder_self_attention_bias[:, :,
i:i + 1, :i + 1]
if self.params["use_full_attention"]:
encoder_outputs = cache.get("encoder_outputs")
else:
encoder_outputs = cache.get("encoder_outputs")[:, i:i + 1]
decoder_outputs = self.decoder_stack(
decoder_input, encoder_outputs, self_attention_bias,
cache.get("encoder_decoder_attention_bias"), cache)
logits = self.embedding_softmax_layer.linear(decoder_outputs)
logits = tf.squeeze(logits, axis=[1])
return logits, cache
return symbols_to_logits_fn
def decode(self, targets, encoder_outputs, attention_bias):
"""Generate logits for each value in the target sequence.
Args:
targets: target values for the output sequence.
int tensor with shape [batch_size, target_length]
encoder_outputs: continuous representation of input sequence.
float tensor with shape [batch_size, input_length, hidden_size]
attention_bias: float tensor with shape [batch_size, 1, 1, input_length]
Returns:
float32 tensor with shape [batch_size, target_length, vocab_size]
"""
with tf.name_scope("decode"):
# Prepare inputs to decoder layers by shifting targets, adding positional
# encoding and applying dropout.
decoder_inputs = self.embedding_softmax_layer(targets)
with tf.name_scope("shift_targets"):
# Shift targets to the right, and remove the last element
decoder_inputs = tf.pad(decoder_inputs,
[[0, 0], [1, 0], [0, 0]])[:, :-1, :]
with tf.name_scope("add_pos_encoding"):
length = tf.shape(decoder_inputs)[1]
decoder_inputs += model_utils.get_position_encoding(
length, self.params["hidden_size"])
if self.train:
decoder_inputs = tf.nn.dropout(
decoder_inputs,
1 - self.params["layer_postprocess_dropout"])
# Run values
decoder_self_attention_bias = model_utils.get_decoder_self_attention_bias(
length)
outputs = self.decoder_stack(decoder_inputs, encoder_outputs,
decoder_self_attention_bias,
attention_bias)
logits = self.embedding_softmax_layer.linear(outputs)
return logits
