ML-GCN（二）模型结构更改

超、凢脫俗 2022-02-15 17:43 262阅读 0赞

背景：我们需要更改相应的模型。

（另，训练测试的时候，训练集上的mAP居然比验证集上的差，比如epoch =1的时候差了 30个百分点，可能程序编写有误，这点我们需要搞懂,查清代码原因。）

**目录**

一、模型定义

1.1 定义位置

1.2 输入参数

1.3 初始化的网络

1.4 结构关系

二、heads网络

2.1 输入参数

2.2 初始化网络结构

2.3 前馈结构

Global max pooling

两层fc

通过fc分组

GALayer1

group内提取特征

所有组及组内合并

三、GAT层替换为fc

3.1 GALayer1

GALayer的输入输出

FC\_layer的参数设置

等价后的fc\_1

四、本地实验汇总

4.1 exp1

4.2 exp2

--------------------

# 一、模型定义 #

## 1.1 定义位置 ##

in general\_train.py

# fixme=============begin=========
        if Config.MODEL == 'hgat_fc':
            import mymodels.hgat_fc as hgat_fc
            model = hgat_fc.HGAT_FC(Config.BACKBONE, groups=Config.GROUPS, nclasses=Config.NCLASSES,
                                    nclasses_per_group=Config.NCLASSES_PER_GROUP,
                                    group_channels=Config.GROUP_CHANNELS, class_channels=Config.CLASS_CHANNELS)

in hgat\_fc.py

class BGATLayer

class BGATLayer(nn.Module):
        """
        Batch GATLayer, modified from:
        Simple GAT layer, similar to https://arxiv.org/abs/1710.10903
        """
    
        def __init__(self, in_features, out_features, dropout, alpha):
            super(BGATLayer, self).__init__()
    
    。。。
    
    class HGAT_FC(nn.Module):
        def __init__(self, backbone, groups, nclasses, nclasses_per_group, group_channels, class_channels):

## 1.2 输入参数 ##

class HGAT_FC(nn.Module):
        def __init__(self, backbone, groups, nclasses, nclasses_per_group, group_channels, class_channels):
            super(HGAT_FC, self).__init__()

**super()** 函数是用于调用父类(超类)的一个方法。

[http://www.runoob.com/python/python-func-super.html][http_www.runoob.com_python_python-func-super.html]

self.groups = groups  组数
    self.nclasses = nclasses  类别数
    self.nclasses_per_group = nclasses_per_group  每组的类别数
    self.group_channels = group_channels  组的channel
    self.class_channels = class_channels   通道的channel
    backbone 根据backbone确定model=resnet101或者resnet50

model = HGAT_FC(backbone='resnet101', groups=12, nclasses=80,
                     nclasses_per_group=[1, 8, 5, 10, 5, 10, 7, 10, 6, 6, 5, 7], group_channels=512, class_channels=256)

## 1.3 初始化的网络 ##

初始化了三个网络，一个model，一个features，一个heads

model

if backbone == 'resnet101':
                model = models.resnet101(pretrained=True)
            elif backbone == 'resnet50':
                model = models.resnet50(pretrained=True)
            else:
                raise Exception()

features (前馈网络)，resnet101,或者resnet50，提取特征用

self.features = nn.Sequential(
                model.conv1,
                model.bn1,
                model.relu,
                model.maxpool,
                model.layer1,
                model.layer2,
                model.layer3,
                model.layer4, )

heads（带GAT的网络，很重要，我们在二中讲

self.heads = Head(self.groups, self.nclasses, 
                    self.nclasses_per_group, group_channels=self.group_channels,
                              class_channels=self.class_channels)

## 1.4 结构关系 ##

先通过

def forward(self, x, inp):
            x = self.features(x)  # [B,2048,H,W]
            x = self.heads(x)
            return x

先通过features，再通过heads

先通过features获得feature-map，纬度\[ B , 2048 , H , W \]，batchSize，2048纬度的特征向量，高，宽

然后将输出通过heads

# 二、heads网络 #

## 2.1 输入参数 ##

class Head(nn.Module):
        def __init__(self, groups, nclasses, nclasses_per_group, group_channels, class_channels):

## 2.2 初始化网络结构 ##

给定一个网络定义了尺寸

#global pooling层
    self.gmp = nn.AdaptiveMaxPool2d(1)
    
    #fc层
    self.reduce_fc = nn.Sequential(utils.BasicLinear(in_channels=2048, out_channels=1024),
                                   utils.BasicLinear(in_channels=1024, out_channels=group_channels), )
    
    #分组fc
    self.group_fcs = nn.ModuleList(
        [utils.ResidualLinearBlock(in_channels=group_channels, reduction=2, out_channels=group_channels)
         for _ in range(groups)])
    
    #类别fc
    self.class_fcs = nn.ModuleList(
        [utils.BasicLinear(in_channels=group_channels, out_channels=class_channels) for _ in range(nclasses)])
    
    #gat1,Graph attention层
    self.gat1 = BGATLayer(in_features=group_channels, out_features=group_channels, dropout=0, alpha=0.2)
    
    self.gat2s = nn.ModuleList(
        [BGATLayer(in_features=class_channels, out_features=class_channels, dropout=0, alpha=0.2) for _ in

## 2.3 前馈结构 ##

先将上一步的进行global max pooling，

### Global max pooling ###

输入纬度\[ B , 2048 , H , W \]

作用Global max pooling

输出纬度\[ B , 2048 \]

x = self.gmp(x).view(x.size(0), x.size(1))  # [B,2048]

### 两层fc ###

输入纬度\[ B , 2048 \]

输出纬度\[B, Group channels\]

经过fc，得到，纬度\[B,  Group\_channels\]，B为batchsize，通过前面提取出来的2048纬度的向量，到1024神经元的隐层，再输出到group channels个输出。

C为group channels，定义为512.

self.reduce_fc = nn.Sequential(utils.BasicLinear(in_channels=2048, out_channels=1024),
                                           utils.BasicLinear(in_channels=1024, out_channels=group_channels), )

x = self.reduce_fc(x)  # [ B , group channels]

### 通过fc分组 ###

输入 \[B ,C\]

C为group channels，512，然后经过 groups=12个fc层，输出到\[ B,  groups ,  group\_channels \]

x = torch.stack([self.group_fcs[i](x) for i in range(self.groups)], dim=1)  
    # [ B,  groups ,  group_channels ]

定义在下面，groups数为12，

self.group_fcs = nn.ModuleList(
                [utils.ResidualLinearBlock(in_channels=group_channels, reduction=2, out_channels=group_channels)
                 for _ in range(groups)])

## GALayer1 ##

x = self.gat1(x)  # [B,groups,group_channels]

输入为\[ B,  groups ,  group\_channels \]， 经过注意力网络，输出为\[ B,  groups ,  group\_channels \]纬度不变，但是每个groups有关联

self.gat1 = BGATLayer(in_features=group_channels, out_features=group_channels, dropout=0, alpha=0.2)

## group内提取特征 ##

for i in range(self.groups):
        inside = []
        for j in range(self.nclasses_per_group[i]):
            inside.append(self.class_fcs[count](x[:, i, :]))  # [B,Group_channels]
            count += 1
        inside = torch.stack(inside, dim=1)  # [B, nclasses_per_group ,Group_channels]
        inside = self.gat2s[i](inside)  # [B, nclasses_per_group, Group_channels]
        outside.append(inside)

遍历group，每个group内针对组内的每个类进行一次卷积，每类输入 \[ B , Group\_channels \]

通过nclasses\_per\_group 个fc输出  \[B, nclasses\_per\_group ,Group\_channels\]

所有组内的类之间通过GAT，输出 \[B, nclasses\_per\_group ,Group\_channels\]

## 所有组及组内合并 ##

x = torch.cat(outside, dim=1)  # [B,nclasses, Group_channels]

前面遍历了组，现在把所有组内的类拼接在一起。

对所有组内做卷积

x = torch.cat([self.fcs[i](x[:, i, :]) for i in range(self.nclasses)], dim=1)  # [B,nclasses]

self.fcs = nn.ModuleList(
                [nn.Sequential(
                    utils.ResidualLinearBlock(in_channels=class_channels, reduction=2, out_channels=class_channels),
                    nn.Linear(in_features=class_channels, out_features=1)
                ) for _ in range(nclasses)])

# 三、GAT层替换为fc #

## 3.1 GALayer1 ##

### GALayer的输入输出 ###

我们现在希望将GATLayer替换为fc

第一个GALayer

输入输出尺寸均为 \[B,groups,group\_channels\]，所以这个GALayer将groups当做节点，此节点可变

self.gat1 = BGATLayer(in_features=group_channels, out_features=group_channels, dropout=0, alpha=0.2)

替换后，需要FC\_layer也是输入输出均为 \[B,groups,group\_channels\]

### FC\_layer的参数设置 ###

输入\[ B ,2048\] ，输出 \[ B, group\_channels\]可见可以将B忽略。

self.reduce_fc = nn.Sequential(utils.BasicLinear(in_channels=2048, out_channels=1024),
                                   utils.BasicLinear(in_channels=1024, out_channels=group_channels), )

等价于GALayer，为输入 \[ B, groups \* group\_channels \] ,输出同样的groups \* group\_channels

### 等价后的fc\_1 ###

定义：

self.fc_replace_GALayer1=utils.BasicLinear(in_channels=groups*group_channels,out_channels=groups*group_channels)

前馈运算:

batch_size = x.size(2)
    group_channels = x.size(0)
    x=x.reshape([batch_size, self.groups*group_channels ])
    
    x=fc_replace_GALayer1(x)
    
    x=x.reshape([batch_size, self.groups , group_channels])

按照要求，

输入输出均为 \[B,groups,group\_channels\]

先做尺寸转换，转换成 \[ B, groups \* group\_channels \]再输入网络，然后再转换回来

\[B,groups,group\_channels\]

# 四、本地实验汇总 #

运行前需要更改general\_train.py之中的，

EXP_NAME，表示实验编号
    RESUME，之前训练的结果，可以继续训练

## 4.1 exp1 ##

代码中，用的正常的gat layer，没有变化

模型存储的位置

checkpoint/coco/exp\_1/  
checkpoint.pth.tar          model\_best\_65.4549.pth.tar  model\_best\_81.2804.pth.tar  model\_best.pth.tar

## 4.2 exp2 ##