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generator.py
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generator.py
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import tensorflow as tf
from tensorflow.python.ops import tensor_array_ops, control_flow_ops
import yaml
with open("SeqGAN.yaml") as stream:
try:
config = yaml.load(stream)
except yaml.YAMLError as exc:
print(exc)
print config
class Generator(object):
def __init__(self, num_emb, batch_size, emb_dim, hidden_dim,
sequence_length, start_token,
learning_rate=config['generator_lr'], reward_gamma=0.95):
self.num_emb = num_emb
self.batch_size = batch_size
self.emb_dim = emb_dim
self.hidden_dim = hidden_dim
self.sequence_length = sequence_length
self.start_token = tf.constant([start_token] * self.batch_size, dtype=tf.int32)
self.learning_rate = tf.Variable(float(learning_rate), trainable=False)
self.reward_gamma = reward_gamma
self.g_params = []
self.d_params = []
self.temperature = 1.0
self.grad_clip = 5.0
# expected reward with shape of 1D
self.expected_reward = tf.Variable(tf.zeros([self.sequence_length]))
with tf.variable_scope('generator'):
self.g_embeddings = tf.Variable(self.init_matrix([self.num_emb, self.emb_dim])) # embedding matrix
self.g_params.append(self.g_embeddings)
self.g_recurrent_unit = self.create_recurrent_unit(self.g_params) # maps h_tm1 to h_t for generator
self.g_output_unit = self.create_output_unit(self.g_params) # maps h_t to o_t (output token logits)
# placeholder definition
self.x = tf.placeholder(tf.int32, shape=[self.batch_size, self.sequence_length]) # sequence of tokens generated by generator
self.rewards = tf.placeholder(tf.float32, shape=[self.batch_size, self.sequence_length]) # get from rollout policy and discriminator
# processed for batch
with tf.device("/cpu:0"):
self.processed_x = tf.transpose(tf.nn.embedding_lookup(self.g_embeddings, self.x), perm=[1, 0, 2]) # seq_length x batch_size x emb_dim
# Initial states
self.h0 = tf.zeros([self.batch_size, self.hidden_dim])
self.h0 = tf.stack([self.h0, self.h0])
# tensor array for generator input and output
gen_o = tensor_array_ops.TensorArray(dtype=tf.float32, size=self.sequence_length,
dynamic_size=False, infer_shape=True)
gen_x = tensor_array_ops.TensorArray(dtype=tf.int32, size=self.sequence_length,
dynamic_size=False, infer_shape=True)
def _g_recurrence(i, x_t, h_tm1, gen_o, gen_x):
h_t = self.g_recurrent_unit(x_t, h_tm1) # hidden_memory_tuple
o_t = self.g_output_unit(h_t) # batch x vocab , logits not prob
log_prob = tf.log(tf.nn.softmax(o_t))
next_token = tf.cast(tf.reshape(tf.multinomial(log_prob, 1), [self.batch_size]), tf.int32)
x_tp1 = tf.nn.embedding_lookup(self.g_embeddings, next_token) # batch x emb_dim
gen_o = gen_o.write(i, tf.reduce_sum(tf.multiply(tf.one_hot(next_token, self.num_emb, 1.0, 0.0),
tf.nn.softmax(o_t)), 1)) # [batch_size] , prob
gen_x = gen_x.write(i, next_token) # indices, batch_size
return i + 1, x_tp1, h_t, gen_o, gen_x
# this recurrence uses tf control ops while loop to the pre-defined sequence length
# start from zero token with embedding and prime with start token
_, _, _, self.gen_o, self.gen_x = control_flow_ops.while_loop(
cond=lambda i, _1, _2, _3, _4: i < self.sequence_length,
body=_g_recurrence,
loop_vars=(tf.constant(0, dtype=tf.int32),
tf.nn.embedding_lookup(self.g_embeddings, self.start_token), self.h0, gen_o, gen_x))
self.gen_x = self.gen_x.stack() # seq_length x batch_size
self.gen_x = tf.transpose(self.gen_x, perm=[1, 0]) # batch_size x seq_length
# supervised pretraining for generator
g_predictions = tensor_array_ops.TensorArray(
dtype=tf.float32, size=self.sequence_length,
dynamic_size=False, infer_shape=True)
# stacked tensor array for embedded input
ta_emb_x = tensor_array_ops.TensorArray(
dtype=tf.float32, size=self.sequence_length)
ta_emb_x = ta_emb_x.unstack(self.processed_x)
def _pretrain_recurrence(i, x_t, h_tm1, g_predictions):
# recurrent method for pretraining
h_t = self.g_recurrent_unit(x_t, h_tm1)
o_t = self.g_output_unit(h_t)
g_predictions = g_predictions.write(i, tf.nn.softmax(o_t)) # batch x vocab_size
x_tp1 = ta_emb_x.read(i)
return i + 1, x_tp1, h_t, g_predictions
# recurrence to the sequence length, with start token
_, _, _, self.g_predictions = control_flow_ops.while_loop(
cond=lambda i, _1, _2, _3: i < self.sequence_length,
body=_pretrain_recurrence,
loop_vars=(tf.constant(0, dtype=tf.int32),
tf.nn.embedding_lookup(self.g_embeddings, self.start_token),
self.h0, g_predictions))
self.g_predictions = tf.transpose(self.g_predictions.stack(), perm=[1, 0, 2]) # batch_size x seq_length x vocab_size
# pretraining loss
# consists of supervised NLL only, without reward signal from D
self.pretrain_loss = -tf.reduce_sum(
tf.one_hot(tf.to_int32(tf.reshape(self.x, [-1])), self.num_emb, 1.0, 0.0) * tf.log(
tf.clip_by_value(tf.reshape(self.g_predictions, [-1, self.num_emb]), 1e-20, 1.0)
)
) / (self.sequence_length * self.batch_size)
# training updates
pretrain_opt = self.g_optimizer(self.learning_rate)
# gradient clipping for stable learning of RNN
self.pretrain_grad, _ = tf.clip_by_global_norm(tf.gradients(self.pretrain_loss, self.g_params), self.grad_clip)
self.pretrain_updates = pretrain_opt.apply_gradients(zip(self.pretrain_grad, self.g_params))
#######################################################################################################
# Unsupervised Training
#######################################################################################################
# unsupervised loss is the adversarial loss, with reward signal from D
# note the element-wise reward signal from the policy rollout
self.g_loss = -tf.reduce_sum(
tf.reduce_sum(
tf.one_hot(tf.to_int32(tf.reshape(self.x, [-1])), self.num_emb, 1.0, 0.0) * tf.log(
tf.clip_by_value(tf.reshape(self.g_predictions, [-1, self.num_emb]), 1e-20, 1.0)
), 1) * tf.reshape(self.rewards, [-1])
)
g_opt = self.g_optimizer(self.learning_rate)
self.g_grad, _ = tf.clip_by_global_norm(tf.gradients(self.g_loss, self.g_params), self.grad_clip)
self.g_updates = g_opt.apply_gradients(zip(self.g_grad, self.g_params))
def generate(self, sess):
outputs = sess.run(self.gen_x)
return outputs
def pretrain_step(self, sess, x):
outputs = sess.run([self.pretrain_updates, self.pretrain_loss], feed_dict={self.x: x})
return outputs
# new implementation
# calculate nll loss without update
# used for observing normal training loss signal, but do not update the supervised gradient
def calculate_nll_loss_step(self, sess, x):
output = sess.run(self.pretrain_loss, feed_dict={self.x: x})
return output
# conditional sequence generation method
# provide the start token ,instead of always zero start
def predict(self, sess, x, start_token):
pred = sess.run(self.gen_x, feed_dict={self.x: x, self.start_token: start_token})
return pred
def init_matrix(self, shape):
return tf.random_normal(shape, stddev=0.1)
def init_vector(self, shape):
return tf.zeros(shape)
def create_recurrent_unit(self, params):
# Weights and Bias for input and hidden tensor
# input gate
self.Wi = tf.Variable(self.init_matrix([self.emb_dim, self.hidden_dim]))
self.Ui = tf.Variable(self.init_matrix([self.hidden_dim, self.hidden_dim]))
self.bi = tf.Variable(self.init_matrix([self.hidden_dim]))
# forget gate
self.Wf = tf.Variable(self.init_matrix([self.emb_dim, self.hidden_dim]))
self.Uf = tf.Variable(self.init_matrix([self.hidden_dim, self.hidden_dim]))
self.bf = tf.Variable(self.init_matrix([self.hidden_dim]))
# output gate
self.Wog = tf.Variable(self.init_matrix([self.emb_dim, self.hidden_dim]))
self.Uog = tf.Variable(self.init_matrix([self.hidden_dim, self.hidden_dim]))
self.bog = tf.Variable(self.init_matrix([self.hidden_dim]))
# internal cell state
self.Wc = tf.Variable(self.init_matrix([self.emb_dim, self.hidden_dim]))
self.Uc = tf.Variable(self.init_matrix([self.hidden_dim, self.hidden_dim]))
self.bc = tf.Variable(self.init_matrix([self.hidden_dim]))
params.extend([
self.Wi, self.Ui, self.bi,
self.Wf, self.Uf, self.bf,
self.Wog, self.Uog, self.bog,
self.Wc, self.Uc, self.bc])
def unit(x, hidden_memory_tm1):
previous_hidden_state, c_prev = tf.unstack(hidden_memory_tm1)
# Input Gate
i = tf.sigmoid(
tf.matmul(x, self.Wi) +
tf.matmul(previous_hidden_state, self.Ui) + self.bi
)
# Forget Gate
f = tf.sigmoid(
tf.matmul(x, self.Wf) +
tf.matmul(previous_hidden_state, self.Uf) + self.bf
)
# Output Gate
o = tf.sigmoid(
tf.matmul(x, self.Wog) +
tf.matmul(previous_hidden_state, self.Uog) + self.bog
)
# New Memory Cell
c_ = tf.nn.tanh(
tf.matmul(x, self.Wc) +
tf.matmul(previous_hidden_state, self.Uc) + self.bc
)
# Final Memory cell
c = f * c_prev + i * c_
# Current Hidden state
current_hidden_state = o * tf.nn.tanh(c)
return tf.stack([current_hidden_state, c])
return unit
def create_output_unit(self, params):
# initialize the weights given the size
self.Wo = tf.Variable(self.init_matrix([self.hidden_dim, self.num_emb]))
self.bo = tf.Variable(self.init_matrix([self.num_emb]))
params.extend([self.Wo, self.bo])
def unit(hidden_memory_tuple):
hidden_state, c_prev = tf.unstack(hidden_memory_tuple)
# hidden_state : batch x hidden_dim
logits = tf.matmul(hidden_state, self.Wo) + self.bo
# output = tf.nn.softmax(logits)
return logits
return unit
def g_optimizer(self, *args, **kwargs):
# adam optimizer for Generator
return tf.train.AdamOptimizer(*args, **kwargs)