bidirectional.py

# Copyright 2017 The TensorFlow Authors All Rights Reserved.
#
# Licensed under the Apache License, Version 2.0 (the "License");
# you may not use this file except in compliance with the License.
# You may obtain a copy of the License at
#
#     http://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS,
# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
# See the License for the specific language governing permissions and
# limitations under the License.
# ==============================================================================

"""Simple bidirectional model definitions."""

from __future__ import absolute_import
from __future__ import division
from __future__ import print_function

import tensorflow as tf

# ZoneoutWrapper.
from regularization import zoneout

FLAGS = tf.app.flags.FLAGS


def discriminator(hparams, sequence, is_training, reuse=None):
  """Define the bidirectional Discriminator graph."""
  sequence = tf.cast(sequence, tf.int32)

  if FLAGS.dis_share_embedding:
    assert hparams.dis_rnn_size == hparams.gen_rnn_size, (
        'If you wish to share Discriminator/Generator embeddings, they must be'
        ' same dimension.')
    with tf.variable_scope('gen/rnn', reuse=True):
      embedding = tf.get_variable('embedding',
                                  [FLAGS.vocab_size, hparams.gen_rnn_size])

  with tf.variable_scope('dis', reuse=reuse):
    cell_fwd = tf.contrib.rnn.LayerNormBasicLSTMCell(
        hparams.dis_rnn_size, forget_bias=1.0, reuse=reuse)
    cell_bwd = tf.contrib.rnn.LayerNormBasicLSTMCell(
        hparams.dis_rnn_size, forget_bias=1.0, reuse=reuse)
    if FLAGS.zoneout_drop_prob > 0.0:
      cell_fwd = zoneout.ZoneoutWrapper(
          cell_fwd,
          zoneout_drop_prob=FLAGS.zoneout_drop_prob,
          is_training=is_training)
      cell_bwd = zoneout.ZoneoutWrapper(
          cell_bwd,
          zoneout_drop_prob=FLAGS.zoneout_drop_prob,
          is_training=is_training)

    state_fwd = cell_fwd.zero_state(FLAGS.batch_size, tf.float32)
    state_bwd = cell_bwd.zero_state(FLAGS.batch_size, tf.float32)

    if not FLAGS.dis_share_embedding:
      embedding = tf.get_variable('embedding',
                                  [FLAGS.vocab_size, hparams.dis_rnn_size])

    rnn_inputs = tf.nn.embedding_lookup(embedding, sequence)
    rnn_inputs = tf.unstack(rnn_inputs, axis=1)

    with tf.variable_scope('rnn') as vs:
      outputs, _, _ = tf.contrib.rnn.static_bidirectional_rnn(
          cell_fwd, cell_bwd, rnn_inputs, state_fwd, state_bwd, scope=vs)

      # Prediction is linear output for Discriminator.
      predictions = tf.contrib.layers.linear(outputs, 1, scope=vs)

      predictions = tf.transpose(predictions, [1, 0, 2])
      return tf.squeeze(predictions, axis=2)