def forward(self, hidden, attn, src_map):
"""
Compute a distribution over the target dictionary
extended by the dynamic dictionary implied by compying
source words.
Args:
hidden (`FloatTensor`): hidden outputs `[batch, tlen, input_size]`
attn (`FloatTensor`): attn for each `[batch, tlen, slen]`
src_map (`FloatTensor`):
A sparse indicator matrix mapping each source word to
its index in the "extended" vocab containing.
`[batch, src_len, extra_words]`
"""
# CHECKS
batch, tlen, _ = hidden.size()
batch_, tlen_, slen = attn.size()
batch, slen_, cvocab = src_map.size()
aeq(tlen, tlen_)
aeq(slen, slen_)
# Original probabilities.
logits = self.linear(hidden)
logits[:, :, constants.PAD] = -self.eps
prob = self.softmax(logits)
# Probability of copying p(z=1) batch.
p_copy = self.sigmoid(self.linear_copy(hidden))
# Probibility of not copying: p_{word}(w) * (1 - p(z))
out_prob = torch.mul(prob, 1 - p_copy.expand_as(prob))
mul_attn = torch.mul(attn, p_copy.expand_as(attn))
copy_prob = torch.bmm(mul_attn,
src_map) # `[batch, tlen, extra_words]`
return torch.cat([out_prob, copy_prob], 2)
def _check_args(self,
src,
lengths=None,
hidden=None):
n_batch, _, _ = src.size()
if lengths is not None:
n_batch_, = lengths.size()
aeq(n_batch, n_batch_)
def forward(self, tgt, memory_bank, state, memory_lengths=None):
"""
Args:
tgt (`LongTensor`): sequences of padded tokens
`[batch x tgt_len x nfeats]`.
memory_bank (`FloatTensor`): vectors from the encoder
`[batch x src_len x hidden]`.
state (:obj:`onmt.models.DecoderState`):
decoder state object to initialize the decoder
memory_lengths (`LongTensor`): the padded source lengths
`[batch]`.
Returns:
(`FloatTensor`,:obj:`onmt.Models.DecoderState`,`FloatTensor`):
* decoder_outputs: output from the decoder (after attn)
`[batch x tgt_len x hidden]`.
* decoder_state: final hidden state from the decoder
* attns: distribution over src at each tgt
`[batch x tgt_len x src_len]`.
"""
# Check
assert isinstance(state, RNNDecoderState)
# tgt.size() returns tgt length and batch
tgt_batch, _, _ = tgt.size()
if self.attn is not None:
memory_batch, _, _ = memory_bank.size()
aeq(tgt_batch, memory_batch)
# END
# Run the forward pass of the RNN.
decoder_final, decoder_outputs, attns = self._run_forward_pass(
tgt, memory_bank, state, memory_lengths=memory_lengths)
coverage = None
if "coverage" in attns:
coverage = attns["coverage"]
# Update the state with the result.
state.update_state(decoder_final, coverage)
return decoder_outputs, state, attns
def __call__(self, scores, align, target):
# CHECKS
batch, tlen, _ = scores.size()
_, _tlen = target.size()
aeq(tlen, _tlen)
_, _tlen = align.size()
aeq(tlen, _tlen)
align = align.view(-1)
target = target.view(-1)
scores = scores.view(-1, scores.size(2))
# Compute unks in align and target for readability
align_unk = align.eq(constants.UNK).float()
align_not_unk = align.ne(constants.UNK).float()
target_unk = target.eq(constants.UNK).float()
target_not_unk = target.ne(constants.UNK).float()
# Copy probability of tokens in source
out = scores.gather(1, align.view(-1, 1) + self.offset).view(-1)
# Set scores for unk to 0 and add eps
out = out.mul(align_not_unk) + self.eps
# Get scores for tokens in target
tmp = scores.gather(1, target.view(-1, 1)).view(-1)
# Regular prob (no unks and unks that can't be copied)
if not self.force_copy:
# Add score for non-unks in target
out = out + tmp.mul(target_not_unk)
# Add score for when word is unk in both align and tgt
out = out + tmp.mul(align_unk).mul(target_unk)
else:
# Forced copy. Add only probability for not-copied tokens
out = out + tmp.mul(align_unk)
loss = -out.log()
return loss
def score(self, h_t, h_s):
"""
Args:
h_t (`FloatTensor`): sequence of queries `[batch x tgt_len x dim]`
h_s (`FloatTensor`): sequence of sources `[batch x src_len x dim]`
Returns:
:obj:`FloatTensor`:
raw attention scores (unnormalized) for each src index
`[batch x tgt_len x src_len]`
"""
# Check input sizes
src_batch, src_len, src_dim = h_s.size()
tgt_batch, tgt_len, tgt_dim = h_t.size()
aeq(src_batch, tgt_batch)
aeq(src_dim, tgt_dim)
aeq(self.dim, src_dim)
if self.attn_type in ["general", "dot"]:
if self.attn_type == "general":
h_t_ = h_t.view(tgt_batch * tgt_len, tgt_dim)
h_t_ = self.linear_in(h_t_)
h_t = h_t_.view(tgt_batch, tgt_len, tgt_dim)
h_s_ = h_s.transpose(1, 2)
# (batch, t_len, d) x (batch, d, s_len) --> (batch, t_len, s_len)
return torch.bmm(h_t, h_s_)
else:
dim = self.dim
wq = self.linear_query(h_t.view(-1, dim))
wq = wq.view(tgt_batch, tgt_len, 1, dim)
wq = wq.expand(tgt_batch, tgt_len, src_len, dim)
uh = self.linear_context(h_s.contiguous().view(-1, dim))
uh = uh.view(src_batch, 1, src_len, dim)
uh = uh.expand(src_batch, tgt_len, src_len, dim)
# (batch, t_len, s_len, d)
wquh = self.tanh(wq + uh)
return self.v(wquh.view(-1, dim)).view(tgt_batch, tgt_len, src_len)
def _run_forward_pass(self, tgt, memory_bank, state, memory_lengths=None):
"""
Private helper for running the specific RNN forward pass.
Must be overriden by all subclasses.
Args:
tgt (LongTensor): a sequence of input tokens tensors
[batch x len x nfeats].
memory_bank (FloatTensor): output(tensor sequence) from the encoder
RNN of size (batch x src_len x hidden_size).
state (FloatTensor): hidden state from the encoder RNN for
initializing the decoder.
memory_lengths (LongTensor): the source memory_bank lengths.
Returns:
decoder_final (Tensor): final hidden state from the decoder.
decoder_outputs (Tensor): output from the decoder (after attn)
`[batch x tgt_len x hidden]`.
attns (Tensor): distribution over src at each tgt
`[batch x tgt_len x src_len]`.
"""
# Initialize local and return variables.
attns = {}
emb = tgt
assert emb.dim() == 3
coverage = state.coverage
if isinstance(self.rnn, nn.GRU):
rnn_output, decoder_final = self.rnn(emb, state.hidden[0])
else:
rnn_output, decoder_final = self.rnn(emb, state.hidden)
# Check
tgt_batch, tgt_len, _ = tgt.size()
output_batch, output_len, _ = rnn_output.size()
aeq(tgt_len, output_len)
aeq(tgt_batch, output_batch)
# END
# Calculate the attention.
if self.attn is not None:
decoder_outputs, p_attn, coverage_v = self.attn(
rnn_output.contiguous(),
memory_bank,
memory_lengths=memory_lengths,
coverage=coverage
)
attns["std"] = p_attn
else:
decoder_outputs = rnn_output.contiguous()
# Update the coverage attention.
if self._coverage:
if coverage_v is None:
coverage = coverage + p_attn \
if coverage is not None else p_attn
else:
coverage = coverage + coverage_v \
if coverage is not None else coverage_v
attns["coverage"] = coverage
decoder_outputs = self.dropout(decoder_outputs)
# Run the forward pass of the copy attention layer.
if self._copy and not self._reuse_copy_attn:
_, copy_attn, _ = self.copy_attn(decoder_outputs,
memory_bank,
memory_lengths=memory_lengths)
attns["copy"] = copy_attn
elif self._copy:
attns["copy"] = attns["std"]
return decoder_final, decoder_outputs, attns
def forward(self, source, memory_bank, memory_lengths=None, coverage=None):
"""
Args:
input (`FloatTensor`): query vectors `[batch x tgt_len x dim]`
memory_bank (`FloatTensor`): source vectors `[batch x src_len x dim]`
memory_lengths (`LongTensor`): the source context lengths `[batch]`
coverage (`FloatTensor`): None (not supported yet)
Returns:
(`FloatTensor`, `FloatTensor`):
* Computed vector `[batch x tgt_len x dim]`
* Attention distribtutions for each query
`[batch x tgt_len x src_len]`
"""
# one step input
assert source.dim() == 3
one_step = True if source.size(1) == 1 else False
batch, source_l, dim = memory_bank.size()
batch_, target_l, dim_ = source.size()
aeq(batch, batch_)
aeq(dim, dim_)
aeq(self.dim, dim)
# compute attention scores, as in Luong et al.
align = self.score(source, memory_bank)
if memory_lengths is not None:
mask = sequence_mask(memory_lengths, max_len=align.size(-1))
mask = mask.unsqueeze(1) # Make it broadcastable.
align.data.masked_fill_(~mask, -float('inf'))
# We adopt coverage attn described in Paulus et al., 2018
# REF: https://arxiv.org/abs/1705.04304
if self._coverage:
maxes = torch.max(align, 2, keepdim=True)[0]
exp_score = torch.exp(align - maxes)
if one_step:
if coverage is None:
# t = 1 in Eq(3) from Paulus et al., 2018
unnormalized_score = exp_score
else:
# t = otherwise in Eq(3) from Paulus et al., 2018
assert coverage.dim() == 3 # B x 1 x slen
unnormalized_score = exp_score.div(coverage + 1e-20)
else:
multiplier = torch.tril(torch.ones(target_l - 1, target_l - 1))
multiplier = multiplier.unsqueeze(0).expand(
batch, *multiplier.size())
multiplier = torch.autograd.Variable(multiplier)
multiplier = multiplier.cuda() if align.is_cuda else multiplier
penalty = torch.bmm(multiplier,
exp_score[:, :-1, :]) # B x tlen-1 x slen
no_penalty = torch.ones_like(penalty[:, -1, :]) # B x slen
penalty = torch.cat([no_penalty.unsqueeze(1), penalty],
dim=1) # B x tlen x slen
assert exp_score.size() == penalty.size()
unnormalized_score = exp_score.div(penalty + 1e-20)
# Eq.(4) from Paulus et al., 2018
align_vectors = unnormalized_score.div(
unnormalized_score.sum(2, keepdim=True))
# Softmax to normalize attention weights
else:
align_vectors = self.softmax(align.view(batch * target_l,
source_l))
align_vectors = align_vectors.view(batch, target_l, source_l)
# each context vector c_t is the weighted average
# over all the source hidden states
c = torch.bmm(align_vectors, memory_bank)
# concatenate
concat_c = torch.cat([c, source], 2).view(batch * target_l, dim * 2)
attn_h = self.linear_out(concat_c).view(batch, target_l, dim)
if self.attn_type in ["general", "dot"]:
attn_h = self.tanh(attn_h)
# Check output sizes
batch_, target_l_, dim_ = attn_h.size()
aeq(target_l, target_l_)
aeq(batch, batch_)
aeq(dim, dim_)
batch_, target_l_, source_l_ = align_vectors.size()
aeq(target_l, target_l_)
aeq(batch, batch_)
aeq(source_l, source_l_)
covrage_vector = None
if self._coverage and one_step:
covrage_vector = exp_score # B x 1 x slen
return attn_h, align_vectors, covrage_vector
