复现transformer
时间: 2023-09-29 16:09:20 浏览: 71
Transformer模型的复现需要涉及到大量的细节和代码实现。以下是一个简单的Transformer模型的复现示例:
首先,我们需要引入必要的库和模块:
```python
import torch
import torch.nn as nn
import torch.nn.functional as F
```
然后,定义Transformer模型的核心组件:多头注意力机制(MultiheadAttention),前馈神经网络(FeedForward),以及编码器层(EncoderLayer)和解码器层(DecoderLayer)。
```python
class MultiheadAttention(nn.Module):
def __init__(self, d_model, n_heads):
super(MultiheadAttention, self).__init__()
self.d_model = d_model
self.n_heads = n_heads
self.head_dim = d_model // n_heads
self.query = nn.Linear(d_model, d_model)
self.key = nn.Linear(d_model, d_model)
self.value = nn.Linear(d_model, d_model)
self.fc = nn.Linear(d_model, d_model)
def forward(self, x, mask=None):
batch_size = x.size(0)
# 计算query、key、value
Q = self.query(x).view(batch_size, -1, self.n_heads, self.head_dim).transpose(1, 2)
K = self.key(x).view(batch_size, -1, self.n_heads, self.head_dim).transpose(1, 2)
V = self.value(x).view(batch_size, -1, self.n_heads, self.head_dim).transpose(1, 2)
# 计算attention得分
scores = torch.matmul(Q, K.transpose(-2, -1)) / torch.sqrt(torch.tensor(self.head_dim, dtype=torch.float))
if mask is not None:
scores = scores.masked_fill(mask == 0, float("-inf"))
# 计算注意力权重
attn_weights = F.softmax(scores, dim=-1)
# 计算注意力值
attention = torch.matmul(attn_weights, V)
# 将多头注意力结果拼接并线性变换
attention = attention.transpose(1, 2).contiguous().view(batch_size, -1, self.n_heads * self.head_dim)
out = self.fc(attention)
return out, attn_weights
class FeedForward(nn.Module):
def __init__(self, d_model, d_ff):
super(FeedForward, self).__init__()
self.fc1 = nn.Linear(d_model, d_ff)
self.fc2 = nn.Linear(d_ff, d_model)
def forward(self, x):
x = self.fc1(x)
x = F.relu(x)
x = self.fc2(x)
return x
class EncoderLayer(nn.Module):
def __init__(self, d_model, n_heads, d_ff):
super(EncoderLayer, self).__init__()
self.multihead_attention = MultiheadAttention(d_model, n_heads)
self.feedforward = FeedForward(d_model, d_ff)
def forward(self, x, mask=None):
attn_out, _ = self.multihead_attention(x, mask=mask)
x = x + attn_out
x = x + self.feedforward(x)
return x
class DecoderLayer(nn.Module):
def __init__(self, d_model, n_heads, d_ff):
super(DecoderLayer, self).__init__()
self.masked_multihead_attention = MultiheadAttention(d_model, n_heads)
self.multihead_attention = MultiheadAttention(d_model, n_heads)
self.feedforward = FeedForward(d_model, d_ff)
def forward(self, x, enc_out, src_mask=None, tgt_mask=None):
attn_out, _ = self.masked_multihead_attention(x, mask=tgt_mask)
x = x + attn_out
attn_out, _ = self.multihead_attention(x, mask=src_mask)
x = x + attn_out
x = x + self.feedforward(x)
return x
```
接下来,定义完整的Transformer模型:
```python
class Transformer(nn.Module):
def __init__(self, vocab_size, d_model, n_heads, d_ff, n_layers):
super(Transformer, self).__init__()
self.embedding = nn.Embedding(vocab_size, d_model)
self.encoder_layers = nn.ModuleList([EncoderLayer(d_model, n_heads, d_ff) for _ in range(n_layers)])
self.decoder_layers = nn.ModuleList([DecoderLayer(d_model, n_heads, d_ff) for _ in range(n_layers)])
self.fc = nn.Linear(d_model, vocab_size)
def forward(self, src, tgt, src_mask=None, tgt_mask=None):
src_embedded = self.embedding(src)
tgt_embedded = self.embedding(tgt)
for encoder_layer in self.encoder_layers:
src_embedded = encoder_layer(src_embedded, mask=src_mask)
for decoder_layer in self.decoder_layers:
tgt_embedded = decoder_layer(tgt_embedded, src_embedded, src_mask=src_mask, tgt_mask=tgt_mask)
output = self.fc(tgt_embedded)
return output
```
这只是一个简单的Transformer模型的复现示例,你可以根据自己的需求进行修改和扩展。注意,这只是一个基本的框架,具体的实现还需要根据实际情况进行调整和完善。