• 🍨 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

• 如果说最经典的神经网络，ResNet肯定是一个，这篇文章是本人学习ResNet的学习笔记，并且用pytorch复现了ResNet50，后面用它做了一个鸟类图像分类demo；
• 欢迎收藏 + 关注，本人将会持续更新

文章目录

• ResNet网络讲解
• • 什么是ResNet？
  • ResNet神经网络突出点
  • 为什么采用残差连接
  • • 模型退化、梯度消失、梯度爆炸
    • 解决方法
  • 残差网络
• ResNet-50复现
• • 1、导入数据
  • • 1、导入库
    • 2、查看数据信息和导入数据
    • 3、展示数据
    • 4、数据导入
    • 5、数据划分
    • 6、动态加载数据
  • 2、构建ResNet-50网络
  • 3、模型训练
  • • 1、构建训练集
    • 2、构建测试集
    • 3、设置超参数
  • 4、模型训练
  • 5、结果可视化
• 参考资料

ResNet网络讲解

什么是ResNet？

ResNet网络是CNN的经典网络架构，是有大神何凯明提出的，主要为了解决随着网络的加深而引起的“ 退化 ”问题，主要用于图像分类。

可以说在如今的CV领域里面，大部分网络结构都有参考ResNet网络思想，无论是在图像分类、目标检测、图像识别上，甚至在Transformer网络模型中，也融合了ResNet网络的思想。

ResNet神经网络突出点

• 网络结构超过1000层：
  • ❔ ❔ 超过1000层网络结构不是很容易么？ 小编在学习深度学习的时候，曾经遇到过这样一个问题，有时候加深网络结构，反而在准确率、损失率上更差，这种现象称为模型“ 退化 ”现象，而ResNet的残差连接可以保证下一层的输出不会比输入差，从而可以加深网络结构。
• 提出残差模块(residual)：这个是ResNet的核心；
• 采用大量的归一化在卷积层与激活函数之间.

为什么采用残差连接

模型退化、梯度消失、梯度爆炸

• 👉 模型退化：指随着网络层数的加深，其效果出现下降趋势，不如层数少的情况。如论文中图示，56层效果不如20层效果；

• 👉 梯度消失：这个是指随着网络层数的增加，反向传播，梯度更新的时候可能会造成前面几层的梯度很小、接近于0，这就会导致权重的更新会特别慢，效率低下。
• 👉 梯度爆炸：指随着网络层数的增加，在反向传播的时候，梯度变得非常大，从而在更新权重的时候，权重值发生大幅度变化，这可能导致网络不稳定，甚至是无法收敛。

解决方法

• 梯度消失、梯度爆炸：在数据预处理和网络层之间加入：BN层(Batch Normalization)，从而对数据进行归一化；
• 模型退化：采用残差连接，如论文图，随着网络层数的增加，损失率更低了。

残差网络

在讲述前，这里先讲述一下恒等映射的概念：

• 恒等映射核心是复制，就是复制网络层，什么也不干。

➿ 可以这么理解：假设在一种网络A的后面添加几层形成新的网络B，如果A的输出经过新的层级变成B的输出没有发送变化，那么就可以说网络A和网络B的错误率是相等的，这样就确保了加深的网络层不会比之前的网络层效果差。

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resent网络说明了，更深的网络结构可以有更好的效果，而解决这个的核心就是残差连接，网络结果如图所示：

上图就是何凯明提出的残差结构，这种结构实现了恒等映射，网络层的输出由两大模块组成：

• 其一：正常的卷积层；
• 其二：有一个分支输出到连接上，这个输出值就是输入的值；

最终结果就是：卷积层输出+分支输出，数学公式如下：

其中F(x)是卷积层的输出，x是分支的输入值。

极端情况：F(x)的网络层中，所有参数都为0，那么H(x)就是恒等映射。这样就确保了最后的错误率不会因为网络层的增加而导致变大。

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在ResNet中有两个不同的ResNet模块，如图所示：

左边：

• 有两层残差单元，输出通道都是3*3
• 使用情况：用于较浅的ResNet网络。

右边：

• 三层残差单元，称为blottlenck模块，作用是：现用1*1卷积进行降维，后用3*3卷积进行特征特权，最后用1*1卷积恢复原来的维度，这个可以很好的减少参数个数，用于较深的神经网络。

下图参考一个csdn大神笔记图：

CNN参数计算公式：卷积核尺寸 * 卷积核速度 * 卷积核组数 == 卷积核尺寸 * 输入特征矩阵深度 * 输出矩阵深度。

ResNet经典的网络结构有ResNet-50，ResNet-101等，本文将用pytorch复现ResNet-50，并用其做一个简单的实验–鸟类图片分类。

ResNet-50网络结果如下：

ResNet-50复现

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

['Bananaquit', 'Black Skimmer', 'Black Throated Bushtiti', 'Cockatoo']

3、展示数据

import matplotlib.pylab as plt  
from PIL import Image # 获取文件名称
data_path_name = "./data/bird_photos/Bananaquit/"
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/bird_photos", 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([0, 1, 0, 1, 2, 1, 1, 0, 2, 2, 1, 2, 1, 3, 1, 2, 2, 2, 2, 1, 2, 1, 2, 2,0, 3, 3, 3, 3, 2, 3, 3])

2、构建ResNet-50网络

import torch.nn.functional as F# 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):super(Identity_block, self).__init__()# 输出通道filter1, filter2, filter3 = filters# 卷积层一self.conv1 = nn.Conv2d(in_channels, filter1, kernel_size=1, stride=1)self.bn1 = nn.BatchNorm2d(filter1)# 卷积层2self.conv2 = nn.Conv2d(filter1, filter2, kernel_size=kernel_size, padding=1)   # 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3self.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, stride=2):super(ConvBlock, self).__init__()filter1, filter2, filter3= filters# 卷积层1self.conv1 = nn.Conv2d(in_channels, filter1, kernel_size=1, stride=stride)self.bn1 = nn.BatchNorm2d(filter1)# 卷积2self.conv2 = nn.Conv2d(filter1, filter2, kernel_size=kernel_size, padding=1) # 需要维持维度不变self.bn2 = nn.BatchNorm2d(filter2)# 卷积3self.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ResNet50
class ResNet50(nn.Module):def __init__(self, classes):   # 类别数量super().__init__()# 头顶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, [64, 64, 256], stride=1)self.part1_2 = Identity_block(256, 3, [64, 64, 256])self.part1_3 = Identity_block(256, 3, [64, 64, 256])# 第二部分self.part2_1 = ConvBlock(256, 3, [128, 128, 512])self.part2_2 = Identity_block(512, 3, [128, 128, 512])self.part2_3 = Identity_block(512, 3, [128, 128, 512])self.part2_4 = Identity_block(512, 3, [128, 128, 512])# 第三部分self.part3_1 = ConvBlock(512, 3, [256, 256, 1024])self.part3_2 = Identity_block(1024, 3, [256, 256, 1024])self.part3_3 = Identity_block(1024, 3, [256, 256, 1024])self.part3_4 = Identity_block(1024, 3, [256, 256, 1024])self.part3_5 = Identity_block(1024, 3, [256, 256, 1024])self.part3_6 = Identity_block(1024, 3, [256, 256, 1024])# 第四部分self.part4_1 = ConvBlock(1024, 3, [512, 512, 2048])self.part4_2 = Identity_block(2048, 3, [512, 512, 2048])self.part4_3 = Identity_block(2048, 3, [512, 512, 2048])# 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 = ResNet50(classes=len(classnames)).to(device)model

ResNet50((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, 64, kernel_size=(1, 1), stride=(1, 1))(bn1): BatchNorm2d(64, eps=1e-05, momentum=0.1, affine=True, track_running_stats=True)(conv2): Conv2d(64, 64, kernel_size=(3, 3), stride=(1, 1), padding=(1, 1))(bn2): BatchNorm2d(64, eps=1e-05, momentum=0.1, affine=True, track_running_stats=True)(conv3): Conv2d(64, 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, 64, kernel_size=(1, 1), stride=(1, 1))(bn1): BatchNorm2d(64, eps=1e-05, momentum=0.1, affine=True, track_running_stats=True)(conv2): Conv2d(64, 64, kernel_size=(3, 3), stride=(1, 1), padding=(1, 1))(bn2): BatchNorm2d(64, eps=1e-05, momentum=0.1, affine=True, track_running_stats=True)(conv3): Conv2d(64, 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, 64, kernel_size=(1, 1), stride=(1, 1))(bn1): BatchNorm2d(64, eps=1e-05, momentum=0.1, affine=True, track_running_stats=True)(conv2): Conv2d(64, 64, kernel_size=(3, 3), stride=(1, 1), padding=(1, 1))(bn2): BatchNorm2d(64, eps=1e-05, momentum=0.1, affine=True, track_running_stats=True)(conv3): Conv2d(64, 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, 128, kernel_size=(1, 1), stride=(2, 2))(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))(bn2): BatchNorm2d(128, eps=1e-05, momentum=0.1, affine=True, track_running_stats=True)(conv3): Conv2d(128, 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, 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))(bn2): BatchNorm2d(128, eps=1e-05, momentum=0.1, affine=True, track_running_stats=True)(conv3): Conv2d(128, 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, 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))(bn2): BatchNorm2d(128, eps=1e-05, momentum=0.1, affine=True, track_running_stats=True)(conv3): Conv2d(128, 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, 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))(bn2): BatchNorm2d(128, eps=1e-05, momentum=0.1, affine=True, track_running_stats=True)(conv3): Conv2d(128, 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, 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))(bn2): BatchNorm2d(256, eps=1e-05, momentum=0.1, affine=True, track_running_stats=True)(conv3): Conv2d(256, 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, 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))(bn2): BatchNorm2d(256, eps=1e-05, momentum=0.1, affine=True, track_running_stats=True)(conv3): Conv2d(256, 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, 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))(bn2): BatchNorm2d(256, eps=1e-05, momentum=0.1, affine=True, track_running_stats=True)(conv3): Conv2d(256, 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, 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))(bn2): BatchNorm2d(256, eps=1e-05, momentum=0.1, affine=True, track_running_stats=True)(conv3): Conv2d(256, 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, 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))(bn2): BatchNorm2d(256, eps=1e-05, momentum=0.1, affine=True, track_running_stats=True)(conv3): Conv2d(256, 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, 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))(bn2): BatchNorm2d(256, eps=1e-05, momentum=0.1, affine=True, track_running_stats=True)(conv3): Conv2d(256, 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, 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))(bn2): BatchNorm2d(512, eps=1e-05, momentum=0.1, affine=True, track_running_stats=True)(conv3): Conv2d(512, 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, 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))(bn2): BatchNorm2d(512, eps=1e-05, momentum=0.1, affine=True, track_running_stats=True)(conv3): Conv2d(512, 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, 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))(bn2): BatchNorm2d(512, eps=1e-05, momentum=0.1, affine=True, track_running_stats=True)(conv3): Conv2d(512, 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=4, bias=True)
)

model(torch.randn(32, 3, 224, 224).to(device)).shape

torch.Size([32, 4])

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

train_acc = []
train_loss = []
test_acc = []
test_loss = []epoches = 80for 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)train_acc.append(epoch_train_acc)train_loss.append(epoch_train_loss)test_acc.append(epoch_test_acc)test_loss.append(epoch_test_loss)# 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")

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()

​

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参考资料

【深度学习】ResNet网络讲解-CSDN博客

K同学啊，训练营文档