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modules.py
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modules.py
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# -*- coding: utf-8 -*-
#/usr/bin/python2
'''
June 2017 by kyubyong park.
https://www.github.com/kyubyong/transformer
'''
from __future__ import print_function
import tensorflow as tf
def normalize(inputs,
epsilon = 1e-8,
scope="ln",
reuse=None):
'''Applies layer normalization.
Args:
inputs: A tensor with 2 or more dimensions, where the first dimension has
`batch_size`.
epsilon: A floating number. A very small number for preventing ZeroDivision Error.
scope: Optional scope for `variable_scope`.
reuse: Boolean, whether to reuse the weights of a previous layer
by the same name.
Returns:
A tensor with the same shape and data dtype as `inputs`.
'''
with tf.variable_scope(scope, reuse=reuse):
inputs_shape = inputs.get_shape()
params_shape = inputs_shape[-1:]
mean, variance = tf.nn.moments(inputs, [-1], keep_dims=True)
beta= tf.Variable(tf.zeros(params_shape))
gamma = tf.Variable(tf.ones(params_shape))
normalized = (inputs - mean) / ( (variance + epsilon) ** (.5) )
outputs = gamma * normalized + beta
return outputs
def embedding(inputs,
vocab_size,
num_units,
zero_pad=True,
scale=True,
scope="embedding",
reuse=None):
'''Embeds a given tensor.
Args:
inputs: A `Tensor` with type `int32` or `int64` containing the ids
to be looked up in `lookup table`.
vocab_size: An int. Vocabulary size.
num_units: An int. Number of embedding hidden units.
zero_pad: A boolean. If True, all the values of the fist row (id 0)
should be constant zeros.
scale: A boolean. If True. the outputs is multiplied by sqrt num_units.
scope: Optional scope for `variable_scope`.
reuse: Boolean, whether to reuse the weights of a previous layer
by the same name.
Returns:
A `Tensor` with one more rank than inputs's. The last dimensionality
should be `num_units`.
For example,
```
import tensorflow as tf
inputs = tf.to_int32(tf.reshape(tf.range(2*3), (2, 3)))
outputs = embedding(inputs, 6, 2, zero_pad=True)
with tf.Session() as sess:
sess.run(tf.global_variables_initializer())
print sess.run(outputs)
>>
[[[ 0. 0. ]
[ 0.09754146 0.67385566]
[ 0.37864095 -0.35689294]]
[[-1.01329422 -1.09939694]
[ 0.7521342 0.38203377]
[-0.04973143 -0.06210355]]]
```
```
import tensorflow as tf
inputs = tf.to_int32(tf.reshape(tf.range(2*3), (2, 3)))
outputs = embedding(inputs, 6, 2, zero_pad=False)
with tf.Session() as sess:
sess.run(tf.global_variables_initializer())
print sess.run(outputs)
>>
[[[-0.19172323 -0.39159766]
[-0.43212751 -0.66207761]
[ 1.03452027 -0.26704335]]
[[-0.11634696 -0.35983452]
[ 0.50208133 0.53509563]
[ 1.22204471 -0.96587461]]]
```
'''
with tf.variable_scope(scope, reuse=reuse):
lookup_table = tf.get_variable('lookup_table',
dtype=tf.float32,
shape=[vocab_size, num_units],
initializer=tf.contrib.layers.xavier_initializer())
if zero_pad:
lookup_table = tf.concat((tf.zeros(shape=[1, num_units]),
lookup_table[1:, :]), 0)
outputs = tf.nn.embedding_lookup(lookup_table, inputs)
if scale:
outputs = outputs * (num_units ** 0.5)
return outputs
def positional_encoding(inputs,
num_units,
zero_pad=True,
scale=True,
scope="positional_encoding",
reuse=None):
'''Sinusoidal Positional_Encoding.
Args:
inputs: A 2d Tensor with shape of (N, T).
num_units: Output dimensionality
zero_pad: Boolean. If True, all the values of the first row (id = 0) should be constant zero
scale: Boolean. If True, the output will be multiplied by sqrt num_units(check details from paper)
scope: Optional scope for `variable_scope`.
reuse: Boolean, whether to reuse the weights of a previous layer
by the same name.
Returns:
A 'Tensor' with one more rank than inputs's, with the dimensionality should be 'num_units'
'''
N, T = inputs.get_shape().as_list()
with tf.variable_scope(scope, reuse=reuse):
position_ind = tf.tile(tf.expand_dims(tf.range(T), 0), [N, 1])
# First part of the PE function: sin and cos argument
position_enc = np.array([
[pos / np.power(10000, 2.*i/num_units) for i in range(num_units)]
for pos in range(T)])
# Second part, apply the cosine to even columns and sin to odds.
position_enc[:, 0::2] = np.sin(position_enc[:, 0::2]) # dim 2i
position_enc[:, 1::2] = np.cos(position_enc[:, 1::2]) # dim 2i+1
# Convert to a tensor
lookup_table = tf.convert_to_tensor(position_enc)
if zero_pad:
lookup_table = tf.concat((tf.zeros(shape=[1, num_units]),
lookup_table[1:, :]), 0)
outputs = tf.nn.embedding_lookup(lookup_table, position_ind)
if scale:
outputs = outputs * num_units**0.5
return outputs
def multihead_attention(queries,
keys,
num_units=None,
num_heads=8,
dropout_rate=0,
is_training=True,
causality=False,
scope="multihead_attention",
reuse=None):
'''Applies multihead attention.
Args:
queries: A 3d tensor with shape of [N, T_q, C_q].
keys: A 3d tensor with shape of [N, T_k, C_k].
num_units: A scalar. Attention size.
dropout_rate: A floating point number.
is_training: Boolean. Controller of mechanism for dropout.
causality: Boolean. If true, units that reference the future are masked.
num_heads: An int. Number of heads.
scope: Optional scope for `variable_scope`.
reuse: Boolean, whether to reuse the weights of a previous layer
by the same name.
Returns
A 3d tensor with shape of (N, T_q, C)
'''
with tf.variable_scope(scope, reuse=reuse):
# Set the fall back option for num_units
if num_units is None:
num_units = queries.get_shape().as_list[-1]
# Linear projections
Q = tf.layers.dense(queries, num_units, activation=tf.nn.relu) # (N, T_q, C)
K = tf.layers.dense(keys, num_units, activation=tf.nn.relu) # (N, T_k, C)
V = tf.layers.dense(keys, num_units, activation=tf.nn.relu) # (N, T_k, C)
# Split and concat
Q_ = tf.concat(tf.split(Q, num_heads, axis=2), axis=0) # (h*N, T_q, C/h)
K_ = tf.concat(tf.split(K, num_heads, axis=2), axis=0) # (h*N, T_k, C/h)
V_ = tf.concat(tf.split(V, num_heads, axis=2), axis=0) # (h*N, T_k, C/h)
# Multiplication
outputs = tf.matmul(Q_, tf.transpose(K_, [0, 2, 1])) # (h*N, T_q, T_k)
# Scale
outputs = outputs / (K_.get_shape().as_list()[-1] ** 0.5)
# Key Masking
key_masks = tf.sign(tf.abs(tf.reduce_sum(keys, axis=-1))) # (N, T_k)
key_masks = tf.tile(key_masks, [num_heads, 1]) # (h*N, T_k)
key_masks = tf.tile(tf.expand_dims(key_masks, 1), [1, tf.shape(queries)[1], 1]) # (h*N, T_q, T_k)
paddings = tf.ones_like(outputs)*(-2**32+1)
outputs = tf.where(tf.equal(key_masks, 0), paddings, outputs) # (h*N, T_q, T_k)
# Causality = Future blinding
if causality:
diag_vals = tf.ones_like(outputs[0, :, :]) # (T_q, T_k)
tril = tf.contrib.linalg.LinearOperatorTriL(diag_vals).to_dense() # (T_q, T_k)
masks = tf.tile(tf.expand_dims(tril, 0), [tf.shape(outputs)[0], 1, 1]) # (h*N, T_q, T_k)
paddings = tf.ones_like(masks)*(-2**32+1)
outputs = tf.where(tf.equal(masks, 0), paddings, outputs) # (h*N, T_q, T_k)
# Activation
outputs = tf.nn.softmax(outputs) # (h*N, T_q, T_k)
# Query Masking
query_masks = tf.sign(tf.abs(tf.reduce_sum(queries, axis=-1))) # (N, T_q)
query_masks = tf.tile(query_masks, [num_heads, 1]) # (h*N, T_q)
query_masks = tf.tile(tf.expand_dims(query_masks, -1), [1, 1, tf.shape(keys)[1]]) # (h*N, T_q, T_k)
outputs *= query_masks # broadcasting. (N, T_q, C)
# Dropouts
outputs = tf.layers.dropout(outputs, rate=dropout_rate, training=tf.convert_to_tensor(is_training))
# Weighted sum
outputs = tf.matmul(outputs, V_) # ( h*N, T_q, C/h)
# Restore shape
outputs = tf.concat(tf.split(outputs, num_heads, axis=0), axis=2 ) # (N, T_q, C)
# Residual connection
outputs += queries
# Normalize
outputs = normalize(outputs) # (N, T_q, C)
return outputs
def feedforward(inputs,
num_units=[2048, 512],
scope="multihead_attention",
reuse=None):
'''Point-wise feed forward net.
Args:
inputs: A 3d tensor with shape of [N, T, C].
num_units: A list of two integers.
scope: Optional scope for `variable_scope`.
reuse: Boolean, whether to reuse the weights of a previous layer
by the same name.
Returns:
A 3d tensor with the same shape and dtype as inputs
'''
with tf.variable_scope(scope, reuse=reuse):
# Inner layer
params = {"inputs": inputs, "filters": num_units[0], "kernel_size": 1,
"activation": tf.nn.relu, "use_bias": True}
outputs = tf.layers.conv1d(**params)
# Readout layer
params = {"inputs": outputs, "filters": num_units[1], "kernel_size": 1,
"activation": None, "use_bias": True}
outputs = tf.layers.conv1d(**params)
# Residual connection
outputs += inputs
# Normalize
outputs = normalize(outputs)
return outputs
def label_smoothing(inputs, epsilon=0.1):
'''Applies label smoothing. See https://arxiv.org/abs/1512.00567.
Args:
inputs: A 3d tensor with shape of [N, T, V], where V is the number of vocabulary.
epsilon: Smoothing rate.
For example,
```
import tensorflow as tf
inputs = tf.convert_to_tensor([[[0, 0, 1],
[0, 1, 0],
[1, 0, 0]],
[[1, 0, 0],
[1, 0, 0],
[0, 1, 0]]], tf.float32)
outputs = label_smoothing(inputs)
with tf.Session() as sess:
print(sess.run([outputs]))
>>
[array([[[ 0.03333334, 0.03333334, 0.93333334],
[ 0.03333334, 0.93333334, 0.03333334],
[ 0.93333334, 0.03333334, 0.03333334]],
[[ 0.93333334, 0.03333334, 0.03333334],
[ 0.93333334, 0.03333334, 0.03333334],
[ 0.03333334, 0.93333334, 0.03333334]]], dtype=float32)]
```
'''
K = inputs.get_shape().as_list()[-1] # number of channels
return ((1-epsilon) * inputs) + (epsilon / K)