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98 lines
3.1 KiB
Python
98 lines
3.1 KiB
Python
# Copyright 2021 Xiaomi Corp. (authors: Fangjun Kuang)
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#
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# See ../../../../LICENSE for clarification regarding multiple authors
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#
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# Licensed under the Apache License, Version 2.0 (the "License");
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# you may not use this file except in compliance with the License.
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# You may obtain a copy of the License at
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#
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# http://www.apache.org/licenses/LICENSE-2.0
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#
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# Unless required by applicable law or agreed to in writing, software
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# distributed under the License is distributed on an "AS IS" BASIS,
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# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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# See the License for the specific language governing permissions and
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# limitations under the License.
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from typing import Optional, Tuple
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import torch
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import torch.nn as nn
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# TODO(fangjun): Support switching between LSTM and GRU
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class Decoder(nn.Module):
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def __init__(
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self,
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vocab_size: int,
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embedding_dim: int,
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blank_id: int,
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num_layers: int,
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hidden_dim: int,
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output_dim: int,
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embedding_dropout: float = 0.0,
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rnn_dropout: float = 0.0,
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):
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"""
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Args:
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vocab_size:
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Number of tokens of the modeling unit including blank.
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embedding_dim:
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Dimension of the input embedding.
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blank_id:
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The ID of the blank symbol.
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num_layers:
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Number of LSTM layers.
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hidden_dim:
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Hidden dimension of LSTM layers.
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output_dim:
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Output dimension of the decoder.
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embedding_dropout:
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Dropout rate for the embedding layer.
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rnn_dropout:
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Dropout for LSTM layers.
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"""
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super().__init__()
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self.embedding = nn.Embedding(
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num_embeddings=vocab_size,
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embedding_dim=embedding_dim,
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padding_idx=blank_id,
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)
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self.embedding_dropout = nn.Dropout(embedding_dropout)
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# TODO(fangjun): Use layer normalized LSTM
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self.rnn = nn.LSTM(
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input_size=embedding_dim,
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hidden_size=hidden_dim,
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num_layers=num_layers,
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batch_first=True,
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dropout=rnn_dropout,
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)
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self.blank_id = blank_id
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self.output_linear = nn.Linear(hidden_dim, output_dim)
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def forward(
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self,
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y: torch.Tensor,
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states: Optional[Tuple[torch.Tensor, torch.Tensor]] = None,
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) -> Tuple[torch.Tensor, Tuple[torch.Tensor, torch.Tensor]]:
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"""
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Args:
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y:
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A 2-D tensor of shape (N, U) with BOS prepended.
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states:
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A tuple of two tensors containing the states information of
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LSTM layers in this decoder.
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Returns:
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Return a tuple containing:
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- rnn_output, a tensor of shape (N, U, C)
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- (h, c), containing the state information for LSTM layers.
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Both are of shape (num_layers, N, C)
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"""
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embedding_out = self.embedding(y)
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embedding_out = self.embedding_dropout(embedding_out)
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rnn_out, (h, c) = self.rnn(embedding_out, states)
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out = self.output_linear(rnn_out)
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return out, (h, c)
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