（超详细）5-YOLOV5改进-添加A2Attention注意力机制

1、在yolov5/models下面新建一个A2Attention.py文件，在里面放入下面的代码

代码如下：

import numpy as np
import torch
from torch import nn
from torch.nn import init
from torch.nn import functional as F



class DoubleAttention(nn.Module):

    def __init__(self, in_channels,c_m=128,c_n=128,reconstruct = True):
        super().__init__()
        self.in_channels=in_channels
        self.reconstruct = reconstruct
        self.c_m=c_m
        self.c_n=c_n
        self.convA=nn.Conv2d(in_channels,c_m,1)
        self.convB=nn.Conv2d(in_channels,c_n,1)
        self.convV=nn.Conv2d(in_channels,c_n,1)
        if self.reconstruct:
            self.conv_reconstruct = nn.Conv2d(c_m, in_channels, kernel_size = 1)
        self.init_weights()


    def init_weights(self):
        for m in self.modules():
            if isinstance(m, nn.Conv2d):
                init.kaiming_normal_(m.weight, mode='fan_out')
                if m.bias is not None:
                    init.constant_(m.bias, 0)
            elif isinstance(m, nn.BatchNorm2d):
                init.constant_(m.weight, 1)
                init.constant_(m.bias, 0)
            elif isinstance(m, nn.Linear):
                init.normal_(m.weight, std=0.001)
                if m.bias is not None:
                    init.constant_(m.bias, 0)

    def forward(self, x):
        b, c, h,w=x.shape
        assert c==self.in_channels
        A=self.convA(x) #b,c_m,h,w
        B=self.convB(x) #b,c_n,h,w
        V=self.convV(x) #b,c_n,h,w
        tmpA=A.view(b,self.c_m,-1)
        attention_maps=F.softmax(B.view(b,self.c_n,-1))
        attention_vectors=F.softmax(V.view(b,self.c_n,-1))
        # step 1: feature gating
        global_descriptors=torch.bmm(tmpA,attention_maps.permute(0,2,1)) #b.c_m,c_n
        # step 2: feature distribution
        tmpZ = global_descriptors.matmul(attention_vectors) #b,c_m,h*w
        tmpZ=tmpZ.view(b,self.c_m,h,w) #b,c_m,h,w
        if self.reconstruct:
            tmpZ=self.conv_reconstruct(tmpZ)

        return tmpZ 

2、找到yolo.py文件，进行更改内容
在29行加一个from models.A2Attention. import DoubleAttention, 保存即可

3、找到自己想要更改的yaml文件，我选择的yolov5s.yaml文件(你可以根据自己需求进行选择），将刚刚写好的模块DoubleAttention加入到yolov5s.yaml里面，并更改一些内容。更改如下

4、在yolo.py里面加入两行代码（335-337）
保存即可！

运行一下