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decoders.py
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decoders.py
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from __future__ import print_function, division
import dynet as dy
import sys
reload(sys)
sys.setdefaultencoding("utf-8")
class Decoder(object):
"""Base Encoder class"""
def __init__(self, pc):
self.pc = pc.add_subcollection('dec')
def init(self, H, y, test=True, update=True):
pass
def next(self, w, c, test=True, state=None):
raise NotImplemented()
def s(self, h, c, e, test=True):
raise NotImplemented()
class LSTMLMDecoder(Decoder):
"""docstring for EmptyEncoder"""
def __init__(self, nl, di, dh, vt, pc, pre_embs=None, dr=0.0, wdr=0.0):
super(LSTMLMDecoder, self).__init__(pc)
# Store hyperparameters
self.nl, self.di, self.dh = nl, di, dh
self.dr, self.wdr = dr, wdr
self.vt = vt
# LSTM Encoder
self.lstm = dy.VanillaLSTMBuilder(self.nl, self.di, self.dh, self.pc)
# Output layer
self.Wo_p = self.pc.add_parameters((self.di, self.dh + self.di), name='Wo')
self.bo_p = self.pc.add_parameters((self.di,), name='bo')
# Embedding matrix
self.E_p = self.pc.add_parameters((self.vt, self.di), name='E')
if pre_embs is not None:
self.E.set_value(pre_embs)
def init(self, H, y, test=True, update=True):
bs = len(y[0])
if not test:
self.lstm.set_dropout(self.dr)
else:
self.lstm.disable_dropout()
# Add encoder to computation graph
self.ds = self.lstm.initial_state(update=update)
if not test:
self.lstm.set_dropout_masks(bs)
self.Wo = self.Wo_p.expr(update)
self.bo = self.bo_p.expr(update)
self.E = self.E_p.expr(update)
def next(self, w, c, test=True, state=None):
e = dy.pick_batch(self.E, w)
if not test:
e = dy.dropout_dim(e, 0, self.wdr)
# Run LSTM
if state is None:
self.ds = self.ds.add_input(e)
next_state = self.ds
else:
next_state = state.add_input(e)
h = next_state.output()
return h, e, next_state
def s(self, h, c, e, test=True):
output = dy.affine_transform([self.bo, self.Wo, dy.concatenate([h, e])])
if not test:
output = dy.dropout(output, self.dr)
# Score
s = self.E * output
return s
class LSTMDecoder(Decoder):
"""docstring for LSTMDecoder"""
def __init__(self, nl, di, de, dh, vt, pc, pre_embs=None, dr=0.0, wdr=0.0):
super(LSTMDecoder, self).__init__(pc)
# Store hyperparameters
self.nl, self.di, self.de, self.dh = nl, di, de, dh
self.dr, self.wdr = dr, wdr
self.vt = vt
# LSTM Encoder
self.lstm = dy.VanillaLSTMBuilder(self.nl, self.di + self.de, self.dh, self.pc)
# Linear layer from last encoding to initial state
self.Wp_p = self.pc.add_parameters((self.di, self.de), name='Wp')
self.bp_p = self.pc.add_parameters((self.di,), name='bp')
# Output layer
self.Wo_p = self.pc.add_parameters((self.di, self.dh + self.de + self.di), name='Wo')
self.bo_p = self.pc.add_parameters((self.di,), name='bo')
# Embedding matrix
self.E_p = self.pc.add_parameters((self.vt, self.di), name='E')
self.b_p = self.pc.add_parameters((self.vt,), init=dy.ConstInitializer(0))
if pre_embs is not None:
self.E.set_value(pre_embs)
def init(self, H, y, test=True, update=True):
bs = len(y[0])
if not test:
self.lstm.set_dropout(self.dr)
else:
self.lstm.disable_dropout()
# Initialize first state of the decoder with the last state of the encoder
self.Wp = self.Wp_p.expr(update)
self.bp = self.bp_p.expr(update)
last_enc = dy.pick(H, index=H.dim()[0][-1] - 1, dim=1)
init_state = dy.affine_transform([self.bp, self.Wp, last_enc])
init_state = [init_state, dy.zeroes((self.dh,), batch_size=bs)]
self.ds = self.lstm.initial_state(init_state, update=update)
# Initialize dropout masks
if not test:
self.lstm.set_dropout_masks(bs)
self.Wo = self.Wo_p.expr(update)
self.bo = self.bo_p.expr(update)
self.E = self.E_p.expr(update)
self.b = self.b_p.expr(False)
def next(self, w, c, test=True, state=None):
e = dy.pick_batch(self.E, w)
if not test:
e = dy.dropout_dim(e, 0, self.wdr)
x = dy.concatenate([e, c])
# Run LSTM
if state is None:
self.ds = self.ds.add_input(x)
next_state = self.ds
else:
next_state = state.add_input(x)
h = next_state.output()
return h, e, next_state
def s(self, h, c, e, test=True):
output = dy.affine_transform([self.bo, self.Wo, dy.concatenate([h, c, e])])
if not test:
output = dy.dropout(output, self.dr)
# Score
s = dy.affine_transform([self.b, self.E, output])
return s
def get_decoder(decoder, nl, di, de, dh, vt, pc, pre_embs=None, dr=0.0, wdr=0.0):
if decoder == 'lm':
return LSTMLMDecoder(nl, di, dh, vt, pc, dr=dr, wdr=wdr, pre_embs=pre_embs)
elif decoder == 'lstm':
return LSTMDecoder(nl, di, de, dh, vt, pc, dr=dr, wdr=wdr, pre_embs=pre_embs)
else:
print('Unknown decoder type "%s", using lstm decoder' % decoder)
return LSTMDecoder(nl, di, de, dh, vt, pc, dr=dr, wdr=wdr, pre_embs=pre_embs)