pytorch - 在 PyTorch 中实现 Luong Attention

Question

我正在尝试实现 Luong et al. 2015 中描述的注意力我自己在 PyTorch 中，但我无法让它工作。下面是我的代码，我现在只对“一般”注意情况感兴趣。我想知道我是否遗漏了任何明显的错误。它可以运行，但似乎没有学习。

class AttnDecoderRNN(nn.Module):
    def __init__(self, hidden_size, output_size, dropout_p=0.1):
        super(AttnDecoderRNN, self).__init__()
        self.hidden_size = hidden_size
        self.output_size = output_size
        self.dropout_p = dropout_p

        self.embedding = nn.Embedding(
            num_embeddings=self.output_size,
            embedding_dim=self.hidden_size
        )
        self.dropout = nn.Dropout(self.dropout_p)
        self.gru = nn.GRU(self.hidden_size, self.hidden_size)
        self.attn = nn.Linear(self.hidden_size, self.hidden_size)
        # hc: [hidden, context]
        self.Whc = nn.Linear(self.hidden_size * 2, self.hidden_size)
        # s: softmax
        self.Ws = nn.Linear(self.hidden_size, self.output_size)

    def forward(self, input, hidden, encoder_outputs):
        embedded = self.embedding(input).view(1, 1, -1)
        embedded = self.dropout(embedded)

        gru_out, hidden = self.gru(embedded, hidden)

        # [0] remove the dimension of directions x layers for now
        attn_prod = torch.mm(self.attn(hidden)[0], encoder_outputs.t())
        attn_weights = F.softmax(attn_prod, dim=1) # eq. 7/8
        context = torch.mm(attn_weights, encoder_outputs)

        # hc: [hidden: context]
        out_hc = F.tanh(self.Whc(torch.cat([hidden[0], context], dim=1)) # eq.5
        output = F.log_softmax(self.Ws(out_hc), dim=1) eq. 6

        return output, hidden, attn_weights

我研究了

中实现的注意力

https://pytorch.org/tutorials/intermediate/seq2seq_translation_tutorial.html

和

https://github.com/spro/practical-pytorch/blob/master/seq2seq-translation/seq2seq-translation.ipynb

• 第一个并不是我正在寻找的确切注意力机制。一个主要缺点是它的注意力取决于序列长度( self.attn = nn.Linear(self.hidden_size * 2, self.max_length) )，这对于长序列来说可能会很昂贵。
• 第二个与论文中描述的更相似，但仍然不一样，因为没有tanh 。此外，更新到最新版本的pytorch( ref )后，速度真的很慢。我也不知道为什么它需要最后一个上下文( ref )。

Answer 1

这个版本有效，并且严格遵循 Luong Attention(一般)的定义。与问题中的主要区别在于 embedding_size 和 hidden_​​size 的分离，这对于实验后的训练似乎很重要。之前，我将它们都设置为相同的大小(256)，这给学习带来了麻烦，并且看起来网络只能学习一半的序列。

class EncoderRNN(nn.Module):
    def __init__(self, input_size, embedding_size, hidden_size,
                 num_layers=1, bidirectional=False, batch_size=1):
        super(EncoderRNN, self).__init__()
        self.hidden_size = hidden_size
        self.num_layers = num_layers
        self.bidirectional = bidirectional
        self.batch_size = batch_size

        self.embedding = nn.Embedding(input_size, embedding_size)

        self.gru = nn.GRU(embedding_size, hidden_size, num_layers,
                          bidirectional=bidirectional)

    def forward(self, input, hidden):
        embedded = self.embedding(input).view(1, 1, -1)
        output, hidden = self.gru(embedded, hidden)
        return output, hidden

    def initHidden(self):
        directions = 2 if self.bidirectional else 1
        return torch.zeros(
            self.num_layers * directions,
            self.batch_size,
            self.hidden_size,
            device=DEVICE
        )


class AttnDecoderRNN(nn.Module):
    def __init__(self, embedding_size, hidden_size, output_size, dropout_p=0):
        super(AttnDecoderRNN, self).__init__()
        self.embedding_size = embedding_size
        self.hidden_size = hidden_size
        self.output_size = output_size
        self.dropout_p = dropout_p

        self.embedding = nn.Embedding(
            num_embeddings=output_size,
            embedding_dim=embedding_size
        )
        self.dropout = nn.Dropout(self.dropout_p)
        self.gru = nn.GRU(embedding_size, hidden_size)
        self.attn = nn.Linear(hidden_size, hidden_size)
        # hc: [hidden, context]
        self.Whc = nn.Linear(hidden_size * 2, hidden_size)
        # s: softmax
        self.Ws = nn.Linear(hidden_size, output_size)

    def forward(self, input, hidden, encoder_outputs):
        embedded = self.embedding(input).view(1, 1, -1)
        embedded = self.dropout(embedded)

        gru_out, hidden = self.gru(embedded, hidden)

        attn_prod = torch.mm(self.attn(hidden)[0], encoder_outputs.t())
        attn_weights = F.softmax(attn_prod, dim=1)
        context = torch.mm(attn_weights, encoder_outputs)

        # hc: [hidden: context]
        hc = torch.cat([hidden[0], context], dim=1)
        out_hc = F.tanh(self.Whc(hc))
        output = F.log_softmax(self.Ws(out_hc), dim=1)

        return output, hidden, attn_weights