深度学习笔记（5）——pytorch实现Att-BiLSTM

1 模型介绍

模型图：

LSTM层：


Attention层
$$\begin{gathered} M=tanh(H) \\ \alpha =softmax({\omega }^T\ast M) \\ r=H{\alpha }^T \\ {h}^{\ast }=tanh(r) \end{gathered}$$
其中
$H为LSTM输出的结果，对应于nn.lstm()输出的第一个结果$
$w^T为训练参数向量，T表示转置$
$\alpha 即为注意力打分函数$
$h^{\ast }为注意力层输出的结果，传递给全连接层$

2 代码实现

import torch
import torch.nn.functional as F
from torch import nn, Tensor


class BiLSTM_Attention(nn.Module):
    def __init__(self, vocab_size, embedding_dim, hidden_size, num_layers, num_classes, device):
        super(BiLSTM_Attention, self).__init__()
        self.hidden_size = hidden_size
        self.num_layers = num_layers
        self.device = device
        # 词嵌入层
        self.embed = nn.Embedding(num_embeddings=vocab_size, embedding_dim=embedding_dim)
        # LSTM
        self.lstm = nn.LSTM(input_size=embedding_dim, hidden_size=hidden_size, num_layers=num_layers, batch_first=True,
                            bidirectional=True)
        # Dropout层
        self.dropout = nn.Dropout(p=0.5)
        # 全连接层
        self.fc = nn.Linear(in_features=hidden_size * 2, out_features=num_classes)

    def attention(self, lstm_out, h_n):
        hidden = h_n.view(-1, self.hidden_size * 2, 1)  # [64, 600, 1] [batch, num_directions * hidden_size, 1]
        weights = torch.transpose(hidden, 1, 2)  # [64, 1, 600] [batch, 1, num_directions * hidden_size]
        H = torch.transpose(lstm_out, 1, 2)  # [64, 600, 200] [batch, num_directions * hidden_size, seq_len]
        M = torch.tanh(H)
        """
        [batch, 1, num_directions * hidden_size] bmm [batch, num_directions * hidden_size, seq_len] = [batch, 1, seq_len]
        torch.bmm([64, 1, 600], [64, 600, 200])->[64, 1, 200]
        """
        att_weights = torch.bmm(weights, M)  # [64, 1, 200] [batch, 1, seq_len]
        alpha = F.softmax(att_weights, dim=2)  # [64, 1, 200] [batch, 1, seq_len]
        r = torch.bmm(H, torch.transpose(alpha, 1, 2)).squeeze(2)  # [64, 600] [batch, num_directions * hidden_size]
        att_out = torch.tanh(r)  # [batch, num_direction * hidden_size]
        return att_out, Tensor.cpu(alpha)

    def forward(self, x):
        # x:[64, 200] [batch_size, seq_len]
        x = self.embed(x)  # [64, 200, 300] [batch, seq_len, hidden_size]
        h0 = torch.zeros(self.num_layers * 2, x.size(0), self.hidden_size).to(self.device)
        c0 = torch.zeros(self.num_layers * 2, x.size(0), self.hidden_size).to(self.device)
        """
        out: [64, 200, 600]  [batch, seq_len, num_directions * hidden_size]
        h_n: [2, 64, 300] [num_layers * num_directions, batch, hidden_size]
        c_n: [2, 64, 300] [num_layers * num_directions, batch, hidden_size]
        """
        out, (h_n, c_n) = self.lstm(x, (h0, c0))
        """
        att_out: [64, 600] [batch, num_directions * hidden_size]
        attention: [64, 1, 200] [batch, 1, seq_len]
        """
        att_out, attention = self.attention(out, h_n)
        logits = self.fc(att_out)  # [64, 10] [batch, num_classes]
        return logits

3 传播过程理解

传播过程中的维度变化
输入层：[batch, seq_len]
词嵌入层：[batch, seq_len, hidden_size]
LSTM层：
out: [batch, seq_len, num_directions * hidden_size]
h_n/c_n: [num_layers * num_directions, batch, hidden_size]
Attention层：
H: [batch, num_directions * hidden_size, seq_len]
M: [batch, num_directions * hidden_size, seq_len]
${\omega }^T$: [batch, 1, seq_len]
$\alpha$: [batch, 1, seq_len]
r: [batch, num_directions * hidden_size]
att_out: [batch, num_directions * hidden_size]
logits: [batch, num_classed]
推导（一个batch为例）

4 实验

以微博情感分析为例

具体代码写在前篇

4 参考文献

论文名称：Attention-Based Bidirectional Long Short-Term Memory Networks for
Relation Classification
论文链接：https://aclanthology.org/P16-2034.pdf
本文参考了：
CSDN：https://blog.csdn.net/qq_34523665/article/details/105654404
GITHUB：https://github.com/onehaitao/Att-BLSTM-relation-extraction