class Self_Attn(nn.Module): """ Self attention Layer""" def __init__(self, in_dim, activation=None): super(Self_Attn, self).__init__() # self.chanel_in = in_dim # self.activation = activation self.query_conv = nn.Conv2d(in_channels=in_dim, out_channels=in_dim // 8, kernel_size=1) self.key_conv = nn.Conv2d(in_channels=in_dim, out_channels=in_dim // 8, kernel_size=1) self.value_conv = nn.Conv2d(in_channels=in_dim, out_channels=in_dim, kernel_size=1) self.gamma = nn.Parameter(torch.zeros(1)) self.softmax = nn.Softmax(dim=-1) # def forward(self, x): """ inputs : x : input feature maps( B X C X W X H) returns : out : self attention value + input feature attention: B X N X N (N is Width*Height) """ # batch,通道数，宽，高 m_batchsize, C, width, height = x.size() # [1, 16, 32, 32] # 步骤1, 通过conv 得出q,k q = self.query_conv(x).view(m_batchsize, -1, width * height).permute(0, 2, 1) # B X CX(N) torch.Size([1, 1024, 2]) k = self.key_conv(x).view(m_batchsize, -1, width * height) # B X C x (*W*H) torch.Size([1, 2, 1024]) # 步骤1, 计算得出v v = self.value_conv(x).view(m_batchsize, -1, width * height) # B X C X N torch.Size([1, 16, 1024]) # 步骤2, 矩阵的乘法 ,q,k进行相乘,得出特征图 # [batch_size,1024,2]*[batch_size,2,1024] energy = torch.bmm(q, k) # transpose check [1, 1024, 1024] # 特征图attention map，通过softmax attention = self.softmax(energy) # BX (N) X (N) torch.Size([1, 1024, 1024]) # 步骤3,v * 特征图= 注意力 # [1,16,1024] * [1,1024,1024]= torch.Size([1, 16, 1024]) out = torch.bmm(v, attention.permute(0, 2, 1)) # torch.Size([1, 16, 1024]) # 重新resize out = out.view(m_batchsize, C, width, height) # torch.Size([1, 16, 32, 32]) # 加上残差 out = self.gamma * out + x return out

这段代码实现了一个Self Attention Layer，其中包含三个卷积层，分别是query_conv、key_conv和value_conv，用于计算注意力的query、key和value。在前向传播中，首先通过query_conv和key_conv计算出query和key，然后计算出注意力矩阵，最后通过value_conv将注意力矩阵与输入特征图相乘得到注意力值，并加上残差。它可以用于图像、文本等任务中，用于提取输入中的重要信息。

相关问题

Transformer and Self-Attention Pytorch代码

以下是使用PyTorch实现Transformer和Self-Attention的示例代码：

## Self-Attention

import torch
import torch.nn as nn

class SelfAttention(nn.Module):
    def __init__(self, embed_size, heads):
        super(SelfAttention, self).__init__()
        self.embed_size = embed_size
        self.heads = heads
        self.head_dim = embed_size // heads
        
        assert (self.head_dim * heads == embed_size), "Embed size needs to be divisible by heads"
        
        self.values = nn.Linear(self.head_dim, self.head_dim, bias=False)
        self.keys = nn.Linear(self.head_dim, self.head_dim, bias=False)
        self.queries = nn.Linear(self.head_dim, self.head_dim, bias=False)
        self.fc_out = nn.Linear(heads * self.head_dim, embed_size)
        
    def forward(self, values, keys, queries, mask):
        # Get number of training examples
        N = queries.shape[0]
        
        value_len, key_len, query_len = values.shape[1], keys.shape[1], queries.shape[1]
        
        # Split embedding into self.heads pieces
        values = values.reshape(N, value_len, self.heads, self.head_dim)
        keys = keys.reshape(N, key_len, self.heads, self.head_dim)
        queries = queries.reshape(N, query_len, self.heads, self.head_dim)
        
        # Transpose to get dimensions batch_size * self.heads * seq_len * self.head_dim
        values = values.permute(0, 2, 1, 3)
        keys = keys.permute(0, 2, 1, 3)
        queries = queries.permute(0, 2, 1, 3)
        
        # Calculate energy
        energy = torch.matmul(queries, keys.permute(0, 1, 3, 2))
        
        if mask is not None:
            energy = energy.masked_fill(mask == 0, float("-1e20"))
        
        # Apply softmax to get attention scores
        attention = torch.softmax(energy / (self.embed_size ** (1/2)), dim=-1)
        
        # Multiply attention scores with values
        out = torch.matmul(attention, values)
        
        # Concatenate and linearly transform output
        out = out.permute(0, 2, 1, 3).reshape(N, query_len, self.heads * self.head_dim)
        out = self.fc_out(out)
        
        return out

## Transformer

import torch
import torch.nn as nn
from torch.nn.modules.activation import MultiheadAttention

class TransformerBlock(nn.Module):
    def __init__(self, embed_size, heads, dropout, forward_expansion):
        super(TransformerBlock, self).__init__()
        self.attention = MultiheadAttention(embed_dim=embed_size, num_heads=heads)
        self.norm1 = nn.LayerNorm(embed_size)
        self.norm2 = nn.LayerNorm(embed_size)
        
        self.feed_forward = nn.Sequential(
            nn.Linear(embed_size, forward_expansion * embed_size),
            nn.ReLU(),
            nn.Linear(forward_expansion * embed_size, embed_size)
        )
        
        self.dropout = nn.Dropout(dropout)
        
    def forward(self, value, key, query, mask):
        attention_output, _ = self.attention(query, key, value, attn_mask=mask)
        
        x = self.dropout(self.norm1(attention_output + query))
        
        forward_output = self.feed_forward(x)
        out = self.dropout(self.norm2(forward_output + x))
        
        return out
        

class Encoder(nn.Module):
    def __init__(self, src_vocab_size, embed_size, num_layers, heads, device, forward_expansion, dropout, max_length):
        super(Encoder, self).__init__()
        self.embed_size = embed_size
        self.device = device
        self.word_embedding = nn.Embedding(src_vocab_size, embed_size)
        self.position_embedding = nn.Embedding(max_length, embed_size)
        
        self.layers = nn.ModuleList([
            TransformerBlock(embed_size, heads, dropout, forward_expansion) for _ in range(num_layers)
        ])
        
        self.dropout = nn.Dropout(dropout)
        
    def forward(self, x, mask):
        N, seq_length = x.shape
        positions = torch.arange(0, seq_length).expand(N, seq_length).to(self.device)
        
        out = self.dropout(self.word_embedding(x) + self.position_embedding(positions))
        
        for layer in self.layers:
            out = layer(out, out, out, mask)
            
        return out
    
    
class DecoderBlock(nn.Module):
    def __init__(self, embed_size, heads, forward_expansion, dropout, device):
        super(DecoderBlock, self).__init__()
        self.norm = nn.LayerNorm(embed_size)
        self.attention = MultiheadAttention(embed_size, heads)
        self.transformer_block = TransformerBlock(embed_size, heads, dropout, forward_expansion)
        self.dropout = nn.Dropout(dropout)
        
    def forward(self, x, value, key, src_mask, trg_mask):
        attention_output, _ = self.attention(x, x, x, attn_mask=trg_mask)
        query = self.dropout(self.norm(attention_output + x))
        out = self.transformer_block(value, key, query, src_mask)
        
        return out
    
    
class Decoder(nn.Module):
    def __init__(self, trg_vocab_size, embed_size, num_layers, heads, forward_expansion, dropout, device, max_length):
        super(Decoder, self).__init__()
        self.embed_size = embed_size
        self.device = device
        self.word_embedding = nn.Embedding(trg_vocab_size, embed_size)
        self.position_embedding = nn.Embedding(max_length, embed_size)
        
        self.layers = nn.ModuleList([
            DecoderBlock(embed_size, heads, forward_expansion, dropout, device) for _ in range(num_layers)
        ])
        
        self.fc_out = nn.Linear(embed_size, trg_vocab_size)
        self.dropout = nn.Dropout(dropout)
        
    def forward(self, x, enc_out, src_mask, trg_mask):
        N, seq_length = x.shape
        positions = torch.arange(0, seq_length).expand(N, seq_length).to(self.device)
        
        x = self.dropout(self.word_embedding(x) + self.position_embedding(positions))
        
        for layer in self.layers:
            x = layer(x, enc_out, enc_out, src_mask, trg_mask)
            
        out = self.fc_out(x)
        
        return out

这些代码可以用于实现Transformer和Self-Attention模型。但这只是示例，你需要根据你的数据和任务来调整这些代码中的各种超参数和结构。

可以设置一个注意力机制（attention mechansim）来学习对应的权重向量Wc，该机制是从一个具有三个全连接层的DNN中获得的吗，python怎么实现

注意力机制（Attention Mechanism）是一种深度学习中的重要技术，用于处理序列数据，比如自然语言处理任务。它允许模型在处理输入时动态地赋予每个元素不同的权重，而不是简单地平均所有信息。这种机制通常不是直接从一个具有三个全连接层的DNN（密集连接神经网络）内生成的，而是作为单独的一个模块插入到DNN架构中。

在Python中，如使用TensorFlow或PyTorch等库，你可以这样实现：

1. TensorFlow:

import tensorflow as tf

class AttentionLayer(tf.keras.layers.Layer):
    def __init__(self, units, **kwargs):
        super(AttentionLayer, self).__init__(**kwargs)
        self.Wc = tf.Variable(tf.random.truncated_normal(shape=(units, 1)), name='weight_vector') # 初始化权重矩阵
        self.dense_1 = tf.keras.layers.Dense(units, activation='relu')
        self.dense_2 = tf.keras.layers.Dense(units)

    def call(self, inputs, previous_attention_weights=None):  
        # 这里假设inputs是经过前几层处理后的张量
        context_vector = self.dense_1(inputs)
        attention_scores = tf.reduce_sum(context_vector * self.Wc, axis=1)  # 计算得分
        if previous_attention_weights is not None:
            attention_scores += previous_attention_weights
        attention_weights = tf.nn.softmax(attention_scores, axis=1)  # 归一化
        context_vector = tf.expand_dims(attention_weights, -1) * inputs  # 加权求和
        return context_vector, attention_weights

2. PyTorch:

import torch
from torch import nn

class AttentionLayer(nn.Module):
    def __init__(self, units):
        super().__init__()
        self.fc1 = nn.Linear(units, units)
        self.fc2 = nn.Linear(units, 1)
        self.Wc = nn.Parameter(torch.randn(1, units))

    def forward(self, x, prev_attn_weights=None):
        context = torch.relu(self.fc1(x))
        scores = torch.matmul(context, self.Wc.t())  # 计算得分
        if prev_attn_weights is not None:
            scores += prev_attn_weights.unsqueeze(1)
        attn_weights = F.softmax(scores, dim=1)
        weighted_input = torch.bmm(attn_weights.unsqueeze(1), x.unsqueeze(2)).squeeze(1)  # 加权求和
        return weighted_input, attn_weights

在这两个例子中，我们创建了一个自定义的注意力层，包含全连接层和一个权重向量。在`forward`函数中，我们计算注意力分数并应用softmax归一化。