深度学习基础--CNN经典网络之分组卷积与ResNext网络实验探究(pytorch复现)

• 🍨 本文为🔗365天深度学习训练营 中的学习记录博客
• 🍖 原作者：K同学啊

前言

• ResNext是分组卷积的开始之作，这里本文将学习ResNext网络；
• 本文复现了ResNext50神经网络，并用其进行了猴痘病分类实验；
• 没有最好的网络。只有最适合的网络，网络不是越复杂，越优秀越好，必须根据实际数据情况，目标要求决定，很多时候，简单的网络反而效果更好；
• 欢迎收藏 + 关注，本人将会持续更新

1、知识简介

1、分组卷积

分组卷积最早出现在AlexNet网络中，在这里将通道数分成两组，采用两个GPU并行提取特征，网络结构如下：

提取到的特征图如下：

作者发现第一组提取的主要是黑白特征，第二组提取的主要是彩色特征，这样分组特征可以更好的提取不同特征数据。

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普通卷积 VS 分组卷积

先看常规卷积，在常规卷积中，输入feature map尺寸为 n 个，输出feature map与卷积和数量相同也是n个，卷积核大小为：c * k * k，n个卷积核总大小为：n * c * k * k，最后输出的维度是：n * h1 * w1，如下图左边所示：

分组卷积，就是对输入的feature map进行分组，然后每组分别卷积。假设输入feature map的尺寸为 c * h * w，输出的feature map为 n，假设分为 g 组，则每组的输入的feature map数量为 c / g，每组输出的feature map为 n / g。但是注意：只是每个卷积核的输入通道数量变成了 c / g，卷积核大小是不变的，每一组卷积核运算后得到了 (n / g) * h1 * w1，最后将各组矩阵进行拼接就可以得出最后的结果，最后输出的维度依然是n * h1 * w1，与常规卷积一样。

参数了对比：

• 常规卷积：c * k * k * n，c通道数，k * k：卷积核矩阵大小，n卷积核数量；
• 分组卷积：(c / g) * k * k * (n / g) * g = k * k * c * n * (1 / g)，从参数了来看，分组卷积更小；

更详细的图如下：

2、split-transform-merge

“Split-Transform-Merge” 是一种常见的设计模式或处理流程，广泛应用于软件开发、数据处理和系统架构中。它的核心思想是将一个复杂的问题分解为更小的部分（Split），对每个部分进行独立的处理或转换（Transform），最后将处理后的结果重新组合（Merge）以完成整体任务。

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1. Split（拆分）

在这一阶段，输入数据或任务被分解成更小、更易于管理的部分。拆分的方式取决于具体问题和上下文。例如：

• 数据拆分：将大数据集分割成多个小块。
• 任务拆分：将一个复杂的任务分解为多个子任务。
• 并行化：通过拆分实现并行处理，提高效率。

示例：

• 分组卷积中，输入通道分组拆分，分组进行卷积。

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2. Transform（转换/处理）

在拆分后，每个部分被独立处理或转换。这是整个流程的核心阶段，通常涉及计算、分析或修改操作。转换的具体内容取决于任务需求：

• 数据清洗、格式转换。
• 算法计算或模型推理。
• 对子任务的独立执行。

示例：

• 分组卷积中 ，每一组分别进行卷积计算，互补干扰。

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3. Merge（合并）

在所有子任务完成后，将处理后的结果重新组合起来，形成最终的输出。合并的方式需要确保结果的完整性和一致性：

• 数据合并：将多个处理后的数据块拼接成完整的数据集。
• 结果整合：将多个子任务的结果汇总为最终答案。
• 冲突解决：如果子任务之间存在冲突或重复，需要在合并阶段解决。

示例：

• 分组卷积中，最后将每一组卷积的结果进行组合。

3、ResNext-50简介

ResNext网络被誉为，分组卷积的开山之作，是何凯明团队在2017年CVPR会与提出的，是ResNet网络的升级版。

在论文中，作者提到了一个普遍存在的现象，提高模型准确率，往往采用的是加深或加宽网络的方法，这种方法虽然有一定效果，但是网络设计的难度和计算了也随着增加，因为不代表网络越深就越好，有时候提升了精度，但是代价也大，就如VGG16提出来的时候，计算了庞大。

在论文中，作者提出了在不额外增加计算代价的情况下，提升网络精度，提出了cardinality概念(cardinality指的是分组卷积中的“组数”).

下图中，左边是(Resnet)右边数(Resnext)的模块差异，在ResNet中，输入具有256个通道特征经过1 * 1卷积压缩到4倍到64个通道特征，然后通过3 * 3卷积核进行特征提取，最后经过 3 * 3卷积核进行还原通道数量输出，并于原来特征进行残差连接。在ResNext中，将256个输入通道特征分成32个组，每个组首先进行64倍压缩到4个通道，然后用3 * 3卷积核大小进行特征提取，最后通过1 * 1卷积核进行通道还原，后会将每个分组的结构进行维度拼接并与原始特征进行残差连接。

cardinatity指的是一个block中所具有的相同分支的数目，即“组数”.

下面进行ResNext-50网络图的搭建(pytorch复现)

2、ResNext-50实验

1、导入数据

1、导入库

import torch  
import torch.nn as nn
import torchvision 
import numpy as np 
import os, PIL, pathlib # 设置设备
device = "cuda" if torch.cuda.is_available() else "cpu"device 

'cuda'

2、查看数据信息和导入数据

数据目录有两个文件：一个数据文件，一个权重。

data_dir = "./data/"data_dir = pathlib.Path(data_dir)# 类别数量
classnames = [str(path).split('/')[0] for path in os.listdir(data_dir)]classnames

['Monkeypox', 'Others']

3、展示数据

import matplotlib.pylab as plt  
from PIL import Image # 获取文件名称
data_path_name = "./data/Others"
data_path_list = [f for f in os.listdir(data_path_name) if f.endswith(('jpg', 'png'))]# 创建画板
fig, axes = plt.subplots(2, 8, figsize=(16, 6))for ax, img_file in zip(axes.flat, data_path_list):path_name = os.path.join(data_path_name, img_file)img = Image.open(path_name) # 打开# 显示ax.imshow(img)ax.axis('off')plt.show()

​

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4、数据导入

from torchvision import transforms, datasets # 数据统一格式
img_height = 224
img_width = 224 data_tranforms = transforms.Compose([transforms.Resize([img_height, img_width]),transforms.ToTensor(),transforms.Normalize(   # 归一化mean=[0.485, 0.456, 0.406],std=[0.229, 0.224, 0.225] )
])# 加载所有数据
total_data = datasets.ImageFolder(root=data_dir, transform=data_tranforms)

5、数据划分

# 大小 8 : 2
train_size = int(len(total_data) * 0.8)
test_size = len(total_data) - train_size train_data, test_data = torch.utils.data.random_split(total_data, [train_size, test_size])

6、动态加载数据

batch_size = 32 train_dl = torch.utils.data.DataLoader(train_data,batch_size=batch_size,shuffle=True
)test_dl = torch.utils.data.DataLoader(test_data,batch_size=batch_size,shuffle=False
)

# 查看数据维度
for data, labels in train_dl:print("data shape[N, C, H, W]: ", data.shape)print("labels: ", labels)break

data shape[N, C, H, W]:  torch.Size([32, 3, 224, 224])
labels:  tensor([1, 0, 0, 0, 1, 1, 0, 0, 0, 1, 0, 0, 1, 1, 1, 0, 1, 0, 1, 0, 1, 0, 1, 0,0, 1, 0, 0, 0, 1, 0, 0])

2、构建ResNext-50网络

ResNet-50网络结构图：

在复现ResNext50网络中，我查阅了不少资料，但是我好像都没怎么看懂那个代码，后面我发现这个就是在ResNet50上加了分组卷积，其他网络结构就是在每一层，第二层的数量是resnet的2倍，后面基于以前搭建的ResNet网络结果进行修改，代码如下所示。

在ResNext50中，有几个参数需要注意：

• 分组卷积：cardinality参数代表分组卷积数量，在Conv2d中groups参数就是分组卷积数量。
• 通道数计算：每组的输出通道数由 group_depth 决定,总输出通道数为 cardinality × group_depth。这里，下面本人搭建的ResNext50网络结构，每一层输入通道数，输出通道数，都是自己手动输入的，故这里group_depth隐藏在filters中(手动计算).

回忆：
Bottleneck 的基本概念

Bottleneck 结构通常由三个卷积层组成，他是ResNet以及其变体的基本网络层单元。

1. 第一个 1×1 卷积：降低输入特征图的通道数，减少后续计算量。
2. 中间的 3×3 卷积：核心特征提取过程。在 ResNeXt 中，这一层使用分组卷积来增强表达能力。
3. 最后一个 1×1 卷积：恢复通道数到原始或者更高的数量，以便与输入特征图进行残差连接。

注意：

• 在ResNext网络结构中，分组卷积只在Bottleneck只在第二层使用

import torch.nn.functional as F# Bottleneck: 分为残差模块一、残差模块二# 定义残差模块一，这个用于处理输入和输出通道一样的情况
'''  
卷积核大小：1       3       1
核心特点：尺寸不变：输入和输出的尺寸保持一致。 没有下采样：没有使用步长大于1的卷积操作，因此没有改变特征图的空间尺寸
'''
class Identity_block(nn.Module):def __init__(self, in_channels, kernel_size, filters, cardinality):super(Identity_block, self).__init__()# 输出通道filter1, filter2, filter3 = filters# 卷积层一, 降维self.conv1 = nn.Conv2d(in_channels, filter1, kernel_size=1, stride=1)self.bn1 = nn.BatchNorm2d(filter1)# 卷积层2, 分组卷积, 核心：特征提取self.conv2 = nn.Conv2d(filter1, filter2, kernel_size=kernel_size, padding=1,groups=cardinality)   # 通过卷积输入输出公式发现，padding=1，可以保证输入和输出尺寸相同self.bn2 = nn.BatchNorm2d(filter2)# 卷积层3， 升维self.conv3 = nn.Conv2d(filter2, filter3, kernel_size=1, stride=1)self.bn3 = nn.BatchNorm2d(filter3)def forward(self, x):# 记录原始值xx = xx = F.relu(self.bn1(self.conv1(x)))x = F.relu(self.bn2(self.conv2(x)))x = self.bn3(self.conv3(x))# 残差连接，输入、输出维度不变x += xxx = F.relu(x)return x # 定义卷积模块二：用于处理输入和输出不一样的情况
'''  
* 卷积核还是：1 3 1
* stride=2
* 这里的分支是采用一个Conv2D，和一个归一化BN层，也是为了处理数据维度吧, 这种维度的变化，可以用ai举例子核心特点：尺寸变化，stride=2降维
'''
class ConvBlock(nn.Module):def __init__(self, in_channels, kernel_size, filters, cardinality, stride=2):super(ConvBlock, self).__init__()filter1, filter2, filter3= filters# 卷积层1, 降维self.conv1 = nn.Conv2d(in_channels, filter1, kernel_size=1, stride=stride)self.bn1 = nn.BatchNorm2d(filter1)# 卷积2， 分组卷积，核心：特征提取self.conv2 = nn.Conv2d(filter1, filter2, kernel_size=kernel_size, padding=1,groups=cardinality) # 需要维持维度不变self.bn2 = nn.BatchNorm2d(filter2)# 卷积3， 降维self.conv3 = nn.Conv2d(filter2, filter3, kernel_size=1, stride=1)  # stride = 1，维持通道不变self.bn3 = nn.BatchNorm2d(filter3)# 用于匹配维度的shortcut卷积，这个就是上面Identity_block的x分支self.shortcut = nn.Conv2d(in_channels, filter3, kernel_size=1, stride=stride)self.shortcut_bn = nn.BatchNorm2d(filter3)def forward(self, x):xx = xx = F.relu(self.bn1(self.conv1(x)))x = F.relu(self.bn2(self.conv2(x)))x = self.bn3(self.conv3(x))temp = self.shortcut_bn(self.shortcut(xx))x += tempx = F.relu(x)return x # 定义ResNext50
class ResNext50(nn.Module):def __init__(self, classes):   # 类别数量super().__init__()# 头顶, resnet以及变体一般都是这个self.conv1 = nn.Conv2d(3, 64, kernel_size=7, stride=2, padding=3)self.bn1 = nn.BatchNorm2d(64)self.max_pool = nn.MaxPool2d(kernel_size=3, stride=2, padding=1)# 第一部分self.part1_1 = ConvBlock(64, 3, [128, 128, 256], cardinality=32, stride=1)self.part1_2 = Identity_block(256, 3, [128, 128, 256], cardinality=32)self.part1_3 = Identity_block(256, 3, [128, 128, 256], cardinality=32)# 第二部分self.part2_1 = ConvBlock(256, 3, [256, 256, 512], cardinality=32)self.part2_2 = Identity_block(512, 3, [256, 256, 512], cardinality=32)self.part2_3 = Identity_block(512, 3, [256, 256, 512], cardinality=32)self.part2_4 = Identity_block(512, 3, [256, 256, 512], cardinality=32)# 第三部分self.part3_1 = ConvBlock(512, 3, [512, 512, 1024], cardinality=32)self.part3_2 = Identity_block(1024, 3, [512, 512, 1024], cardinality=32)self.part3_3 = Identity_block(1024, 3, [512, 512, 1024], cardinality=32)self.part3_4 = Identity_block(1024, 3, [512, 512, 1024], cardinality=32)self.part3_5 = Identity_block(1024, 3, [512, 512, 1024], cardinality=32)self.part3_6 = Identity_block(1024, 3, [512, 512, 1024], cardinality=32)# 第四部分self.part4_1 = ConvBlock(1024, 3, [1024, 1024, 2048], cardinality=32)self.part4_2 = Identity_block(2048, 3, [1024, 1024, 2048], cardinality=32)self.part4_3 = Identity_block(2048, 3, [1024, 1024, 2048], cardinality=32)# 平均池化self.avg_pool = nn.AvgPool2d(kernel_size=7)# 全连接self.fn1 = nn.Linear(2048, classes)def forward(self, x):# 头部x = F.relu(self.bn1(self.conv1(x)))x = self.max_pool(x)x = self.part1_1(x)x = self.part1_2(x)x = self.part1_3(x)x = self.part2_1(x)x = self.part2_2(x)x = self.part2_3(x)x = self.part2_4(x)x = self.part3_1(x)x = self.part3_2(x)x = self.part3_3(x)x = self.part3_4(x)x = self.part3_5(x)x = self.part3_6(x)x = self.part4_1(x)x = self.part4_2(x)x = self.part4_3(x)x = self.avg_pool(x)x = x.view(x.size(0), -1)  # 扁平化x = self.fn1(x)return x model = ResNext50(classes=len(classnames)).to(device)model

ResNext50((conv1): Conv2d(3, 64, kernel_size=(7, 7), stride=(2, 2), padding=(3, 3))(bn1): BatchNorm2d(64, eps=1e-05, momentum=0.1, affine=True, track_running_stats=True)(max_pool): MaxPool2d(kernel_size=3, stride=2, padding=1, dilation=1, ceil_mode=False)(part1_1): ConvBlock((conv1): Conv2d(64, 128, kernel_size=(1, 1), stride=(1, 1))(bn1): BatchNorm2d(128, eps=1e-05, momentum=0.1, affine=True, track_running_stats=True)(conv2): Conv2d(128, 128, kernel_size=(3, 3), stride=(1, 1), padding=(1, 1), groups=32)(bn2): BatchNorm2d(128, eps=1e-05, momentum=0.1, affine=True, track_running_stats=True)(conv3): Conv2d(128, 256, kernel_size=(1, 1), stride=(1, 1))(bn3): BatchNorm2d(256, eps=1e-05, momentum=0.1, affine=True, track_running_stats=True)(shortcut): Conv2d(64, 256, kernel_size=(1, 1), stride=(1, 1))(shortcut_bn): BatchNorm2d(256, eps=1e-05, momentum=0.1, affine=True, track_running_stats=True))(part1_2): Identity_block((conv1): Conv2d(256, 128, kernel_size=(1, 1), stride=(1, 1))(bn1): BatchNorm2d(128, eps=1e-05, momentum=0.1, affine=True, track_running_stats=True)(conv2): Conv2d(128, 128, kernel_size=(3, 3), stride=(1, 1), padding=(1, 1), groups=32)(bn2): BatchNorm2d(128, eps=1e-05, momentum=0.1, affine=True, track_running_stats=True)(conv3): Conv2d(128, 256, kernel_size=(1, 1), stride=(1, 1))(bn3): BatchNorm2d(256, eps=1e-05, momentum=0.1, affine=True, track_running_stats=True))(part1_3): Identity_block((conv1): Conv2d(256, 128, kernel_size=(1, 1), stride=(1, 1))(bn1): BatchNorm2d(128, eps=1e-05, momentum=0.1, affine=True, track_running_stats=True)(conv2): Conv2d(128, 128, kernel_size=(3, 3), stride=(1, 1), padding=(1, 1), groups=32)(bn2): BatchNorm2d(128, eps=1e-05, momentum=0.1, affine=True, track_running_stats=True)(conv3): Conv2d(128, 256, kernel_size=(1, 1), stride=(1, 1))(bn3): BatchNorm2d(256, eps=1e-05, momentum=0.1, affine=True, track_running_stats=True))(part2_1): ConvBlock((conv1): Conv2d(256, 256, kernel_size=(1, 1), stride=(2, 2))(bn1): BatchNorm2d(256, eps=1e-05, momentum=0.1, affine=True, track_running_stats=True)(conv2): Conv2d(256, 256, kernel_size=(3, 3), stride=(1, 1), padding=(1, 1), groups=32)(bn2): BatchNorm2d(256, eps=1e-05, momentum=0.1, affine=True, track_running_stats=True)(conv3): Conv2d(256, 512, kernel_size=(1, 1), stride=(1, 1))(bn3): BatchNorm2d(512, eps=1e-05, momentum=0.1, affine=True, track_running_stats=True)(shortcut): Conv2d(256, 512, kernel_size=(1, 1), stride=(2, 2))(shortcut_bn): BatchNorm2d(512, eps=1e-05, momentum=0.1, affine=True, track_running_stats=True))(part2_2): Identity_block((conv1): Conv2d(512, 256, kernel_size=(1, 1), stride=(1, 1))(bn1): BatchNorm2d(256, eps=1e-05, momentum=0.1, affine=True, track_running_stats=True)(conv2): Conv2d(256, 256, kernel_size=(3, 3), stride=(1, 1), padding=(1, 1), groups=32)(bn2): BatchNorm2d(256, eps=1e-05, momentum=0.1, affine=True, track_running_stats=True)(conv3): Conv2d(256, 512, kernel_size=(1, 1), stride=(1, 1))(bn3): BatchNorm2d(512, eps=1e-05, momentum=0.1, affine=True, track_running_stats=True))(part2_3): Identity_block((conv1): Conv2d(512, 256, kernel_size=(1, 1), stride=(1, 1))(bn1): BatchNorm2d(256, eps=1e-05, momentum=0.1, affine=True, track_running_stats=True)(conv2): Conv2d(256, 256, kernel_size=(3, 3), stride=(1, 1), padding=(1, 1), groups=32)(bn2): BatchNorm2d(256, eps=1e-05, momentum=0.1, affine=True, track_running_stats=True)(conv3): Conv2d(256, 512, kernel_size=(1, 1), stride=(1, 1))(bn3): BatchNorm2d(512, eps=1e-05, momentum=0.1, affine=True, track_running_stats=True))(part2_4): Identity_block((conv1): Conv2d(512, 256, kernel_size=(1, 1), stride=(1, 1))(bn1): BatchNorm2d(256, eps=1e-05, momentum=0.1, affine=True, track_running_stats=True)(conv2): Conv2d(256, 256, kernel_size=(3, 3), stride=(1, 1), padding=(1, 1), groups=32)(bn2): BatchNorm2d(256, eps=1e-05, momentum=0.1, affine=True, track_running_stats=True)(conv3): Conv2d(256, 512, kernel_size=(1, 1), stride=(1, 1))(bn3): BatchNorm2d(512, eps=1e-05, momentum=0.1, affine=True, track_running_stats=True))(part3_1): ConvBlock((conv1): Conv2d(512, 512, kernel_size=(1, 1), stride=(2, 2))(bn1): BatchNorm2d(512, eps=1e-05, momentum=0.1, affine=True, track_running_stats=True)(conv2): Conv2d(512, 512, kernel_size=(3, 3), stride=(1, 1), padding=(1, 1), groups=32)(bn2): BatchNorm2d(512, eps=1e-05, momentum=0.1, affine=True, track_running_stats=True)(conv3): Conv2d(512, 1024, kernel_size=(1, 1), stride=(1, 1))(bn3): BatchNorm2d(1024, eps=1e-05, momentum=0.1, affine=True, track_running_stats=True)(shortcut): Conv2d(512, 1024, kernel_size=(1, 1), stride=(2, 2))(shortcut_bn): BatchNorm2d(1024, eps=1e-05, momentum=0.1, affine=True, track_running_stats=True))(part3_2): Identity_block((conv1): Conv2d(1024, 512, kernel_size=(1, 1), stride=(1, 1))(bn1): BatchNorm2d(512, eps=1e-05, momentum=0.1, affine=True, track_running_stats=True)(conv2): Conv2d(512, 512, kernel_size=(3, 3), stride=(1, 1), padding=(1, 1), groups=32)(bn2): BatchNorm2d(512, eps=1e-05, momentum=0.1, affine=True, track_running_stats=True)(conv3): Conv2d(512, 1024, kernel_size=(1, 1), stride=(1, 1))(bn3): BatchNorm2d(1024, eps=1e-05, momentum=0.1, affine=True, track_running_stats=True))(part3_3): Identity_block((conv1): Conv2d(1024, 512, kernel_size=(1, 1), stride=(1, 1))(bn1): BatchNorm2d(512, eps=1e-05, momentum=0.1, affine=True, track_running_stats=True)(conv2): Conv2d(512, 512, kernel_size=(3, 3), stride=(1, 1), padding=(1, 1), groups=32)(bn2): BatchNorm2d(512, eps=1e-05, momentum=0.1, affine=True, track_running_stats=True)(conv3): Conv2d(512, 1024, kernel_size=(1, 1), stride=(1, 1))(bn3): BatchNorm2d(1024, eps=1e-05, momentum=0.1, affine=True, track_running_stats=True))(part3_4): Identity_block((conv1): Conv2d(1024, 512, kernel_size=(1, 1), stride=(1, 1))(bn1): BatchNorm2d(512, eps=1e-05, momentum=0.1, affine=True, track_running_stats=True)(conv2): Conv2d(512, 512, kernel_size=(3, 3), stride=(1, 1), padding=(1, 1), groups=32)(bn2): BatchNorm2d(512, eps=1e-05, momentum=0.1, affine=True, track_running_stats=True)(conv3): Conv2d(512, 1024, kernel_size=(1, 1), stride=(1, 1))(bn3): BatchNorm2d(1024, eps=1e-05, momentum=0.1, affine=True, track_running_stats=True))(part3_5): Identity_block((conv1): Conv2d(1024, 512, kernel_size=(1, 1), stride=(1, 1))(bn1): BatchNorm2d(512, eps=1e-05, momentum=0.1, affine=True, track_running_stats=True)(conv2): Conv2d(512, 512, kernel_size=(3, 3), stride=(1, 1), padding=(1, 1), groups=32)(bn2): BatchNorm2d(512, eps=1e-05, momentum=0.1, affine=True, track_running_stats=True)(conv3): Conv2d(512, 1024, kernel_size=(1, 1), stride=(1, 1))(bn3): BatchNorm2d(1024, eps=1e-05, momentum=0.1, affine=True, track_running_stats=True))(part3_6): Identity_block((conv1): Conv2d(1024, 512, kernel_size=(1, 1), stride=(1, 1))(bn1): BatchNorm2d(512, eps=1e-05, momentum=0.1, affine=True, track_running_stats=True)(conv2): Conv2d(512, 512, kernel_size=(3, 3), stride=(1, 1), padding=(1, 1), groups=32)(bn2): BatchNorm2d(512, eps=1e-05, momentum=0.1, affine=True, track_running_stats=True)(conv3): Conv2d(512, 1024, kernel_size=(1, 1), stride=(1, 1))(bn3): BatchNorm2d(1024, eps=1e-05, momentum=0.1, affine=True, track_running_stats=True))(part4_1): ConvBlock((conv1): Conv2d(1024, 1024, kernel_size=(1, 1), stride=(2, 2))(bn1): BatchNorm2d(1024, eps=1e-05, momentum=0.1, affine=True, track_running_stats=True)(conv2): Conv2d(1024, 1024, kernel_size=(3, 3), stride=(1, 1), padding=(1, 1), groups=32)(bn2): BatchNorm2d(1024, eps=1e-05, momentum=0.1, affine=True, track_running_stats=True)(conv3): Conv2d(1024, 2048, kernel_size=(1, 1), stride=(1, 1))(bn3): BatchNorm2d(2048, eps=1e-05, momentum=0.1, affine=True, track_running_stats=True)(shortcut): Conv2d(1024, 2048, kernel_size=(1, 1), stride=(2, 2))(shortcut_bn): BatchNorm2d(2048, eps=1e-05, momentum=0.1, affine=True, track_running_stats=True))(part4_2): Identity_block((conv1): Conv2d(2048, 1024, kernel_size=(1, 1), stride=(1, 1))(bn1): BatchNorm2d(1024, eps=1e-05, momentum=0.1, affine=True, track_running_stats=True)(conv2): Conv2d(1024, 1024, kernel_size=(3, 3), stride=(1, 1), padding=(1, 1), groups=32)(bn2): BatchNorm2d(1024, eps=1e-05, momentum=0.1, affine=True, track_running_stats=True)(conv3): Conv2d(1024, 2048, kernel_size=(1, 1), stride=(1, 1))(bn3): BatchNorm2d(2048, eps=1e-05, momentum=0.1, affine=True, track_running_stats=True))(part4_3): Identity_block((conv1): Conv2d(2048, 1024, kernel_size=(1, 1), stride=(1, 1))(bn1): BatchNorm2d(1024, eps=1e-05, momentum=0.1, affine=True, track_running_stats=True)(conv2): Conv2d(1024, 1024, kernel_size=(3, 3), stride=(1, 1), padding=(1, 1), groups=32)(bn2): BatchNorm2d(1024, eps=1e-05, momentum=0.1, affine=True, track_running_stats=True)(conv3): Conv2d(1024, 2048, kernel_size=(1, 1), stride=(1, 1))(bn3): BatchNorm2d(2048, eps=1e-05, momentum=0.1, affine=True, track_running_stats=True))(avg_pool): AvgPool2d(kernel_size=7, stride=7, padding=0)(fn1): Linear(in_features=2048, out_features=2, bias=True)
)

3、模型训练

1、构建训练集

def train(dataloader, model, loss_fn, optimizer):size = len(dataloader.dataset)batch_size = len(dataloader)train_acc, train_loss = 0, 0 for X, y in dataloader:X, y = X.to(device), y.to(device)# 训练pred = model(X)loss = loss_fn(pred, y)# 梯度下降法optimizer.zero_grad()loss.backward()optimizer.step()# 记录train_loss += loss.item()train_acc += (pred.argmax(1) == y).type(torch.float).sum().item()train_acc /= sizetrain_loss /= batch_sizereturn train_acc, train_loss

2、构建测试集

def test(dataloader, model, loss_fn):size = len(dataloader.dataset)batch_size = len(dataloader)test_acc, test_loss = 0, 0 with torch.no_grad():for X, y in dataloader:X, y = X.to(device), y.to(device)pred = model(X)loss = loss_fn(pred, y)test_loss += loss.item()test_acc += (pred.argmax(1) == y).type(torch.float).sum().item()test_acc /= sizetest_loss /= batch_sizereturn test_acc, test_loss

3、设置超参数

loss_fn = nn.CrossEntropyLoss()  # 损失函数     
learn_lr = 1e-4            # 超参数
optimizer = torch.optim.Adam(model.parameters(), lr=learn_lr)   # 优化器

4、模型训练

import copy train_acc = []
train_loss = []
test_acc = []
test_loss = []epoches = 50best_acc = 0for i in range(epoches):model.train()epoch_train_acc, epoch_train_loss = train(train_dl, model, loss_fn, optimizer)model.eval()epoch_test_acc, epoch_test_loss = test(test_dl, model, loss_fn)# 保存最佳模型到 best_model     if epoch_test_acc > best_acc:         best_acc   = epoch_test_acc         best_model = copy.deepcopy(model)  # 拷贝最好模型train_acc.append(epoch_train_acc)train_loss.append(epoch_train_loss)test_acc.append(epoch_test_acc)test_loss.append(epoch_test_loss)# 获取当前的学习率     lr = optimizer.state_dict()['param_groups'][0]['lr']# 输出template = ('Epoch:{:2d}, Train_acc:{:.1f}%, Train_loss:{:.3f}, Test_acc:{:.1f}%, Test_loss:{:.3f}')print(template.format(i + 1, epoch_train_acc*100, epoch_train_loss, epoch_test_acc*100, epoch_test_loss))print("Done")PATH = './best_model.pth'  # 保存的参数文件名 
torch.save(best_model.state_dict(), PATH)

Epoch: 1, Train_acc:62.3%, Train_loss:0.696, Test_acc:66.4%, Test_loss:0.604
Epoch: 2, Train_acc:67.9%, Train_loss:0.620, Test_acc:69.9%, Test_loss:0.580
Epoch: 3, Train_acc:69.5%, Train_loss:0.580, Test_acc:68.3%, Test_loss:0.603
Epoch: 4, Train_acc:71.6%, Train_loss:0.547, Test_acc:73.9%, Test_loss:0.530
Epoch: 5, Train_acc:74.7%, Train_loss:0.519, Test_acc:75.1%, Test_loss:0.520
Epoch: 6, Train_acc:78.2%, Train_loss:0.464, Test_acc:67.8%, Test_loss:0.683
Epoch: 7, Train_acc:78.1%, Train_loss:0.459, Test_acc:69.0%, Test_loss:0.652
Epoch: 8, Train_acc:80.8%, Train_loss:0.411, Test_acc:72.7%, Test_loss:0.643
Epoch: 9, Train_acc:84.8%, Train_loss:0.362, Test_acc:74.8%, Test_loss:0.575
Epoch:10, Train_acc:87.4%, Train_loss:0.314, Test_acc:77.9%, Test_loss:0.536
Epoch:11, Train_acc:89.3%, Train_loss:0.266, Test_acc:79.0%, Test_loss:0.505
Epoch:12, Train_acc:89.4%, Train_loss:0.260, Test_acc:78.3%, Test_loss:0.601
Epoch:13, Train_acc:90.7%, Train_loss:0.226, Test_acc:81.4%, Test_loss:0.493
Epoch:14, Train_acc:93.9%, Train_loss:0.159, Test_acc:80.4%, Test_loss:0.616
Epoch:15, Train_acc:93.8%, Train_loss:0.152, Test_acc:80.4%, Test_loss:0.620
Epoch:16, Train_acc:92.2%, Train_loss:0.190, Test_acc:82.3%, Test_loss:0.621
Epoch:17, Train_acc:94.0%, Train_loss:0.142, Test_acc:82.3%, Test_loss:0.582
Epoch:18, Train_acc:95.8%, Train_loss:0.106, Test_acc:79.3%, Test_loss:0.625
Epoch:19, Train_acc:95.5%, Train_loss:0.127, Test_acc:81.1%, Test_loss:0.625
Epoch:20, Train_acc:95.4%, Train_loss:0.113, Test_acc:83.0%, Test_loss:0.482
Epoch:21, Train_acc:96.7%, Train_loss:0.087, Test_acc:83.0%, Test_loss:0.667
Epoch:22, Train_acc:97.3%, Train_loss:0.083, Test_acc:80.4%, Test_loss:0.695
Epoch:23, Train_acc:97.1%, Train_loss:0.077, Test_acc:83.7%, Test_loss:0.634
Epoch:24, Train_acc:96.6%, Train_loss:0.086, Test_acc:82.5%, Test_loss:0.732
Epoch:25, Train_acc:96.6%, Train_loss:0.098, Test_acc:83.9%, Test_loss:0.711
Epoch:26, Train_acc:96.0%, Train_loss:0.107, Test_acc:75.3%, Test_loss:0.821
Epoch:27, Train_acc:95.6%, Train_loss:0.105, Test_acc:81.6%, Test_loss:0.596
Epoch:28, Train_acc:96.7%, Train_loss:0.088, Test_acc:84.4%, Test_loss:0.606
Epoch:29, Train_acc:97.5%, Train_loss:0.071, Test_acc:86.5%, Test_loss:0.615
Epoch:30, Train_acc:98.2%, Train_loss:0.051, Test_acc:80.4%, Test_loss:0.772
Epoch:31, Train_acc:98.5%, Train_loss:0.041, Test_acc:83.7%, Test_loss:0.694
Epoch:32, Train_acc:98.5%, Train_loss:0.048, Test_acc:82.8%, Test_loss:0.671
Epoch:33, Train_acc:97.7%, Train_loss:0.064, Test_acc:84.1%, Test_loss:0.745
Epoch:34, Train_acc:98.4%, Train_loss:0.054, Test_acc:83.7%, Test_loss:0.661
Epoch:35, Train_acc:98.2%, Train_loss:0.068, Test_acc:83.0%, Test_loss:0.605
Epoch:36, Train_acc:96.8%, Train_loss:0.086, Test_acc:83.2%, Test_loss:0.551
Epoch:37, Train_acc:97.8%, Train_loss:0.063, Test_acc:82.3%, Test_loss:0.739
Epoch:38, Train_acc:97.6%, Train_loss:0.065, Test_acc:83.0%, Test_loss:0.583
Epoch:39, Train_acc:98.2%, Train_loss:0.045, Test_acc:83.4%, Test_loss:0.697
Epoch:40, Train_acc:98.1%, Train_loss:0.048, Test_acc:82.5%, Test_loss:0.710
Epoch:41, Train_acc:98.2%, Train_loss:0.054, Test_acc:83.2%, Test_loss:0.564
Epoch:42, Train_acc:98.4%, Train_loss:0.051, Test_acc:85.5%, Test_loss:0.514
Epoch:43, Train_acc:99.0%, Train_loss:0.025, Test_acc:83.9%, Test_loss:0.663
Epoch:44, Train_acc:99.1%, Train_loss:0.029, Test_acc:85.5%, Test_loss:0.594
Epoch:45, Train_acc:98.3%, Train_loss:0.036, Test_acc:84.6%, Test_loss:0.719
Epoch:46, Train_acc:98.7%, Train_loss:0.036, Test_acc:84.4%, Test_loss:0.631
Epoch:47, Train_acc:97.7%, Train_loss:0.055, Test_acc:81.4%, Test_loss:0.643
Epoch:48, Train_acc:98.7%, Train_loss:0.040, Test_acc:85.1%, Test_loss:0.607
Epoch:49, Train_acc:98.8%, Train_loss:0.037, Test_acc:80.2%, Test_loss:0.897
Epoch:50, Train_acc:98.6%, Train_loss:0.042, Test_acc:84.4%, Test_loss:0.601
Done

5、结果可视化

import matplotlib.pyplot as plt
#隐藏警告
import warnings
warnings.filterwarnings("ignore")               #忽略警告信息epochs_range = range(epoches)plt.figure(figsize=(12, 3))
plt.subplot(1, 2, 1)plt.plot(epochs_range, train_acc, label='Training Accuracy')
plt.plot(epochs_range, test_acc, label='Test Accuracy')
plt.legend(loc='lower right')
plt.title('Training Accuracy')plt.subplot(1, 2, 2)
plt.plot(epochs_range, train_loss, label='Training Loss')
plt.plot(epochs_range, test_loss, label='Test Loss')
plt.legend(loc='upper right')
plt.title('Training= Loss')
plt.show()

​

​

6、模型评估

# 加载最好模型
best_model.load_state_dict(torch.load(PATH, map_location=device)) 
# 模型测试
epoch_test_acc, epoch_test_loss = test(test_dl, best_model, loss_fn)print(epoch_test_acc, epoch_test_loss)

0.8648018648018648 0.6145411878824234

3、参考资料

• 深度学习——分类之ResNeXt - 知乎
• 通义 - 你的个人AI助手
• ResNeXt代码复现＋超详细注释（PyTorch）-CSDN博客