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# Copyright (c) Facebook, Inc. and its affiliates.
#
# This source code is licensed under the MIT license found in the
# LICENSE file in the root directory of this source tree.
import torch.nn as nn
import torch
import torch.nn.functional as F
class LocationAttention(nn.Module):
"""
Attention-Based Models for Speech Recognition
https://arxiv.org/pdf/1506.07503.pdf
:param int encoder_dim: # projection-units of encoder
:param int decoder_dim: # units of decoder
:param int attn_dim: attention dimension
:param int conv_dim: # channels of attention convolution
:param int conv_kernel_size: filter size of attention convolution
"""
def __init__(self, attn_dim, encoder_dim, decoder_dim,
attn_state_kernel_size, conv_dim, conv_kernel_size,
scaling=2.0):
super(LocationAttention, self).__init__()
self.attn_dim = attn_dim
self.decoder_dim = decoder_dim
self.scaling = scaling
self.proj_enc = nn.Linear(encoder_dim, attn_dim)
self.proj_dec = nn.Linear(decoder_dim, attn_dim, bias=False)
self.proj_attn = nn.Linear(conv_dim, attn_dim, bias=False)
self.conv = nn.Conv1d(attn_state_kernel_size, conv_dim,
2 * conv_kernel_size + 1,
padding=conv_kernel_size, bias=False)
self.proj_out = nn.Sequential(nn.Tanh(), nn.Linear(attn_dim, 1))
self.proj_enc_out = None # cache
def clear_cache(self):
self.proj_enc_out = None
def forward(self, encoder_out, encoder_padding_mask, decoder_h, attn_state):
"""
:param torch.Tensor encoder_out: padded encoder hidden state B x T x D
:param torch.Tensor encoder_padding_mask: encoder padding mask
:param torch.Tensor decoder_h: decoder hidden state B x D
:param torch.Tensor attn_prev: previous attention weight B x K x T
:return: attention weighted encoder state (B, D)
:rtype: torch.Tensor
:return: previous attention weights (B x T)
:rtype: torch.Tensor
"""
bsz, seq_len, _ = encoder_out.size()
if self.proj_enc_out is None:
self.proj_enc_out = self.proj_enc(encoder_out)
# B x K x T -> B x C x T
attn = self.conv(attn_state)
# B x C x T -> B x T x C -> B x T x D
attn = self.proj_attn(attn.transpose(1, 2))
if decoder_h is None:
decoder_h = encoder_out.new_zeros(bsz, self.decoder_dim)
dec_h = self.proj_dec(decoder_h).view(bsz, 1, self.attn_dim)
out = self.proj_out(attn + self.proj_enc_out + dec_h).squeeze(2)
out.masked_fill_(encoder_padding_mask, -float("inf"))
w = F.softmax(self.scaling * out, dim=1)
c = torch.sum(encoder_out * w.view(bsz, seq_len, 1), dim=1)
return c, w
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