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ae5944a Mar 28, 2018
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#! -*- coding: utf-8 -*-
from keras import backend as K
from keras.engine.topology import Layer
class Position_Embedding(Layer):
def __init__(self, size=None, mode='sum', **kwargs):
self.size = size #必须为偶数
self.mode = mode
super(Position_Embedding, self).__init__(**kwargs)
def call(self, x):
if (self.size == None) or (self.mode == 'sum'):
self.size = int(x.shape[-1])
batch_size,seq_len = K.shape(x)[0],K.shape(x)[1]
position_j = 1. / K.pow(10000., \
2 * K.arange(self.size / 2, dtype='float32' \
) / self.size)
position_j = K.expand_dims(position_j, 0)
position_i = K.cumsum(K.ones_like(x[:,:,0]), 1)-1 #K.arange不支持变长,只好用这种方法生成
position_i = K.expand_dims(position_i, 2)
position_ij = K.dot(position_i, position_j)
position_ij = K.concatenate([K.cos(position_ij), K.sin(position_ij)], 2)
if self.mode == 'sum':
return position_ij + x
elif self.mode == 'concat':
return K.concatenate([position_ij, x], 2)
def compute_output_shape(self, input_shape):
if self.mode == 'sum':
return input_shape
elif self.mode == 'concat':
return (input_shape[0], input_shape[1], input_shape[2]+self.size)
class Attention(Layer):
def __init__(self, nb_head, size_per_head, **kwargs):
self.nb_head = nb_head
self.size_per_head = size_per_head
self.output_dim = nb_head*size_per_head
super(Attention, self).__init__(**kwargs)
def build(self, input_shape):
self.WQ = self.add_weight(name='WQ',
shape=(input_shape[0][-1], self.output_dim),
initializer='glorot_uniform',
trainable=True)
self.WK = self.add_weight(name='WK',
shape=(input_shape[1][-1], self.output_dim),
initializer='glorot_uniform',
trainable=True)
self.WV = self.add_weight(name='WV',
shape=(input_shape[2][-1], self.output_dim),
initializer='glorot_uniform',
trainable=True)
super(Attention, self).build(input_shape)
def Mask(self, inputs, seq_len, mode='mul'):
if seq_len == None:
return inputs
else:
mask = K.one_hot(seq_len[:,0], K.shape(inputs)[1])
mask = 1 - K.cumsum(mask, 1)
for _ in range(len(inputs.shape)-2):
mask = K.expand_dims(mask, 2)
if mode == 'mul':
return inputs * mask
if mode == 'add':
return inputs - (1 - mask) * 1e12
def call(self, x):
#如果只传入Q_seq,K_seq,V_seq,那么就不做Mask
#如果同时传入Q_seq,K_seq,V_seq,Q_len,V_len,那么对多余部分做Mask
if len(x) == 3:
Q_seq,K_seq,V_seq = x
Q_len,V_len = None,None
elif len(x) == 5:
Q_seq,K_seq,V_seq,Q_len,V_len = x
#对Q、K、V做线性变换
Q_seq = K.dot(Q_seq, self.WQ)
Q_seq = K.reshape(Q_seq, (-1, K.shape(Q_seq)[1], self.nb_head, self.size_per_head))
Q_seq = K.permute_dimensions(Q_seq, (0,2,1,3))
K_seq = K.dot(K_seq, self.WK)
K_seq = K.reshape(K_seq, (-1, K.shape(K_seq)[1], self.nb_head, self.size_per_head))
K_seq = K.permute_dimensions(K_seq, (0,2,1,3))
V_seq = K.dot(V_seq, self.WV)
V_seq = K.reshape(V_seq, (-1, K.shape(V_seq)[1], self.nb_head, self.size_per_head))
V_seq = K.permute_dimensions(V_seq, (0,2,1,3))
#计算内积,然后mask,然后softmax
A = K.batch_dot(Q_seq, K_seq, axes=[3,3]) / self.size_per_head**0.5
A = K.permute_dimensions(A, (0,3,2,1))
A = self.Mask(A, V_len, 'add')
A = K.permute_dimensions(A, (0,3,2,1))
A = K.softmax(A)
#输出并mask
O_seq = K.batch_dot(A, V_seq, axes=[3,2])
O_seq = K.permute_dimensions(O_seq, (0,2,1,3))
O_seq = K.reshape(O_seq, (-1, K.shape(O_seq)[1], self.output_dim))
O_seq = self.Mask(O_seq, Q_len, 'mul')
return O_seq
def compute_output_shape(self, input_shape):
return (input_shape[0][0], input_shape[0][1], self.output_dim)