深度学习本科课程 实验4 卷积神经网络

二维卷积实验

1.1 任务内容

1. 手写二维卷积的实现，并在至少一个数据集上进行实验，从训练时间、预测精 度、Loss变化等角度分析实验结果（最好使用图表展示）（只用循环几轮即可）
2. 使用torch.nn实现二维卷积，并在至少一个数据集上进行实验，从训练时间、 预测精度、Loss变化等角度分析实验结果（最好使用图表展示）
3. 不同超参数的对比分析（包括卷积层数、卷积核大小、batchsize、lr等）选其 中至少1-2个进行分析

1.2 任务思路及代码

# 读取数据
import os
import numpy as np
import torch
import PIL
from PIL import Image
import cv2
from torch import nn
device = torch.device("cuda" if torch.cuda.is_available() else "cpu")
print(f'当前使用的device为{device}')

data_dir = "./resizedImages"
bus_dir = data_dir + os.sep +'bus'
car_dir = data_dir + os.sep +'car'
truck_dir = data_dir + os.sep +'truck'

if not os.path.exists(data_dir):
    os.mkdir(data_dir)
if not os.path.exists(car_dir):
    os.mkdir(car_dir)
if not os.path.exists(bus_dir):
    os.mkdir(bus_dir)
if not os.path.exists(truck_dir):
    os.mkdir(truck_dir)

width = 200
height = width
path = "./车辆分类数据集/bus"
busData =  os.listdir(path)
for img_item in busData:
    if img_item != "desktop.ini":
        img = Image.open(path + os.sep + img_item)
        img = img.resize((width, height), Image.LANCZOS)
        img.save(bus_dir + os.sep + img_item)

path = "./车辆分类数据集/car"
carData =  os.listdir(path)
for img_item in carData:
    if img_item == "desktop.ini":
        continue
    img = Image.open(path + os.sep + img_item)
    img = img.resize((width, height), Image.LANCZOS)
    img.save(car_dir + os.sep + img_item)
    
path = "./车辆分类数据集/truck"
truckData =  os.listdir(path)
for img_item in truckData:
    if img_item == "desktop.ini":
        continue
    img = Image.open(path + os.sep + img_item)
    img = img.resize((width, height), Image.LANCZOS)
    img.save(truck_dir + os.sep + img_item)
# 已缩放处理过，存储在根目录下resizedImages文件夹中各分类下

# 超参数设定
epochs = 10
lr = 0.001
batch_size = 32

# 划分数据集
import random
import shutil
import torchvision
import torchvision.transforms as transforms
from torch.utils.data import DataLoader
from torchvision.datasets import ImageFolder

train_dir = './Classfication-train_data'
test_dir = './Classfication-test_data'

if not os.path.exists(train_dir) or not os.path.exists(test_dir):
    os.mkdir(train_dir)
    os.mkdir(test_dir)
vehicles = os.listdir(data_dir)

bus_dir = train_dir + os.sep +'bus'
car_dir = train_dir + os.sep +'car'
truck_dir = train_dir + os.sep +'truck'
if not os.path.exists(car_dir):
    os.mkdir(car_dir)
if not os.path.exists(bus_dir):
    os.mkdir(bus_dir)
if not os.path.exists(truck_dir):
    os.mkdir(truck_dir)

bus_dir = test_dir + os.sep +'bus'
car_dir = test_dir + os.sep +'car'
truck_dir = test_dir + os.sep +'truck'
if not os.path.exists(car_dir):
    os.mkdir(car_dir)
if not os.path.exists(bus_dir):
    os.mkdir(bus_dir)
if not os.path.exists(truck_dir):
    os.mkdir(truck_dir)
# 项目结构：
# ./（根目录）
#     resizedImages/
#         bus/
#         car/
#         truck/
#     Classfication-train_data/
#         bus/
#         car/
#         truck/
#     Classfication-test_data/
#         bus/
#         car/
#         truck/

split_rate = 0.8
# 训练集：测试集=8：2
# 开始拷贝

for folder in vehicles: # car, bus, truck
    print(folder)
    file_names = np.array(os.listdir(os.path.join(data_dir,folder)))
    train_number = int(len(file_names) * split_rate)
    total_number = list(range(len(file_names)))
    print(f"训练集数量: {train_number}, 测试集数量{len(file_names) - train_number}")
    if len(os.listdir(train_dir + os.sep + folder)) != 0:
           continue
    random.shuffle(total_number)  # 打乱下标
    # 获得打乱下标后的训练集和测试集的数据
    train_files = file_names[total_number[0: train_number]]
    test_files = file_names[total_number[train_number:]]
    
    for file in train_files:
        if file == "desktop.ini":
            continue
        path_train = os.path.join(data_dir, folder) + os.sep + file
        path_train_copy = train_dir + os.sep + folder + os.sep + file
        shutil.copy(path_train, path_train_copy) # 将文件复制到训练集文件夹
        
    for file in test_files:
        if file == "desktop.ini":
            continue
        path_test = os.path.join(data_dir, folder) + os.sep + file
        path_test_copy = test_dir + os.sep + folder + os.sep + file
        shutil.copy(path_test, path_test_copy)  # 讲文件复制到测试集文件夹


transform = transforms.Compose(
    [transforms.ToTensor(),
     transforms.Normalize((0.5,0.5,0.5), (0.5,0.5,0.5))])
    # 归一化
# 相关参数
train_data = ImageFolder(root=train_dir, transform=transform)
train_loader = DataLoader(dataset=train_data, shuffle=True, batch_size=batch_size)
test_data = ImageFolder(root=test_dir, transform=transform)
test_loader = DataLoader(dataset=test_data, shuffle=True, batch_size=batch_size)

print()
print(f"训练集数量 :{len(train_data)}")
print(f"测试集数量 :{len(test_data)}")

from torch import nn
# 定义卷积
def corr2d(X, K, kernel_size):
    '''
    X, shape(batch_size,H,W)
    kernel_size, shape(k_h, k_w)
    '''
    batch_size, H,W = X.shape
    k_h, k_w = kernel_size
    Y = torch.zeros((batch_size, H-k_h+1, W-k_w+1)).to(device)
    for i in range(Y.shape[0]):
        for j in range(Y.shape[1]):
            Y[:, i, j] = (X[:,i: i+k_h, j:j+k_w]*K).sum(dim=2).sum(dim=1)
    return Y

# 多通道输入
# 卷积核通道数 = 输入通道数
def corr2d_multi_in(X, K, kernel_size):
    res = corr2d(X[:, 0, :, :], K[0, :, :],kernel_size)
    for i in range(1, X.shape[1]):
        res += corr2d(X[:,i,:,:], K[i,:,:], kernel_size)
    return res
    
# 多通道输出
# 输出通道数 = 卷积核个数
def corr2d_multi_in_out(X, K, kernel_size):
    return torch.stack([corr2d_multi_in(X, k, kernel_size) for k in K])

# 将卷积运算封装成卷积层
class myConv2d(nn.Module):
    def __init__(self, in_channels, out_channels, kernel_size):
        super(myConv2d, self).__init__()
        if isinstance(kernel_size, int):  
            self.kernel_size = (kernel_size, kernel_size)
            self.weight = nn.Parameter(torch.randn((out_channels, in_channels) + self.kernel_size)).to(device)
            self.bias = nn.Parameter(torch.randn(out_channels, 1,1))
    def forward(self, x):
        return corr2d_multi_in_out(x, self.weight, self.kernel_size) + self.bias

# 手动实现二维 CNN
import torch.nn.functional as F

class myCNN(torch.nn.Module):
    def __init__(self, num_classes):
        super(myCNN, self).__init__()
        self.conv = nn.Sequential(
            myConv2d(in_channels=3, out_channels=32, kernel_size=3),
            torch.nn.BatchNorm2d(32),
            torch.nn.ReLU(inplace=True) 
        )
        self.fc = torch.nn.Linear(32, num_classes)
    def forward(self, X):
        # 根据实验要求，图片经过一层卷积，输出（batch_size, C_out, H, W)
        out = self.conv(X)
        # 使用平均池化层将图片大小变为1*1
        out = F.avg_pool2d(out, 198) # 图片大小为200*200，卷积后为198
        out = out.squeeze()
        # 输入到全连接层
        out = self.fc(out)
        return out

# nn实现二维卷积
class nnCNN(nn.Module):
    def __init__(self, num_classes):
        super(nnCNN,self).__init__()
        # 三层卷积
        self.conv = nn.Sequential(
            # 这里设置了填充，因为图片大小为 200*200，运算过程出现了小数，这里是考虑不周到的地方
            nn.Conv2d(in_channels=3,out_channels=32,kernel_size=3,stride=1,padding=1),
            nn.BatchNorm2d(32),
            nn.ReLU(inplace=True),
            nn.Conv2d(in_channels=32,out_channels=64,kernel_size=3,stride=1,padding=1),
            nn.BatchNorm2d(64),
            nn.ReLU(inplace=True),
            nn.Conv2d(in_channels=64,out_channels=128,kernel_size=3,stride=1,padding=1),
            nn.BatchNorm2d(128),
            nn.ReLU(inplace=True)
        )
        self.fc = nn.Linear(128,num_classes)
    def forward(self,X):
        out= self.conv(X)
        out = F.avg_pool2d(out, kernel_size=out.size()[2:])
        out = out.view(out.size(0), -1)
        out = self.fc(out)
        return out

# 定义训练函数
import time
from torch.nn import CrossEntropyLoss
from torch.optim import SGD
criterion = CrossEntropyLoss()
criterion = criterion.to(device)
# 测试加训练
def train_with_test(net, train_loader, test_loader,batch_size=32, epochs=10, lr=0.001, optimizer=None, disp=True, skip=False):
    if disp:
        print(net)
    if optimizer == None:
        optimizer = SGD(net.parameters(), lr=lr) 
    train_batch_num = len(train_loader)
    train_loss_list = []
    train_acc= []
    train_loss_in_batch, train_acc_in_batch = [], []
    test_loss_list =[]
    test_acc=[]
    begin_time = time.time()
    for epoch in range(epochs):
        train_loss, acc = 0, 0
        train_sample_num = 0
        # acc_num = 0
        jmp = 25
        for batch_idx, (data, target) in enumerate(train_loader):
            # batch_size = 32
            if len(data) != batch_size:
                continue
            # if batch_idx == 2:
            #     break
            if skip and batch_idx < jmp:
                continue
            if skip and batch_idx % 2 == 0:
                continue # 加快训练，卷积训练太慢，主要看手动卷积的效果
            tb1 = time.time()
            data, target = data.to(device), target.to(device)
            prediction = net(data)
            loss = criterion(prediction, target)
            optimizer.zero_grad()
            loss.backward()
            optimizer.step()
            # 循环内损失率
            train_loss_in_batch.append(loss.to('cpu')/len(prediction))
            # 循环损失率
            train_loss += loss.item()
            
            # 循环内正确率
            train_batch_acc_num = (prediction.argmax(dim=1)==target).sum()
            train_acc_in_batch.append(train_batch_acc_num.to('cpu')/len(prediction))
            # 循环正确率
            acc += train_batch_acc_num
            
            train_sample_num += len(prediction)

            tb2=time.time()
            if skip or batch_idx % 4 == 0:
                print(f"\t|Train-in-batch:{batch_idx+1}/{len(train_loader)}, loss:{train_loss/train_sample_num}, acc:{acc/train_sample_num}, 耗时:{tb2-tb1}s")
            
        train_acc.append(acc.to('cpu')/train_sample_num)
        train_loss_list.append(train_loss/train_sample_num)
        # 测试
        test_batch_num = len(test_loader)
        total_loss = 0
        sample_num2=0
        acc2 = 0
        with torch.no_grad():
            for batch_idx, (data, target) in enumerate (test_loader):
                if len(data) != batch_size:
                    continue
                # if batch_idx == 2:
                #     break

                data, target = data.to(device), target.to(device)
                prediction = net(data)
                loss = criterion(prediction, target)
                # 循环总损失
                total_loss += loss.item()
                sample_num2 += len(prediction)
                # 循环总正确
                acc_num2 = (prediction.argmax(dim=1)==target).sum()
                acc2 += acc_num2

            test_loss_list.append(total_loss/sample_num2)
            test_acc.append(acc2.to('cpu')/sample_num2)
        print('***epoch: %d***train loss: %.5f***train acc:%5f***test loss:%.5f***test acc:%5f' % 
              (epoch + 1, train_loss_list[epoch], train_acc[epoch],test_loss_list[epoch],test_acc[epoch]))
        print()
        
    end_time = time.time()
    print('%d轮总用时: %.2fs'%(epochs, end_time-begin_time))
    # 返回全部损失，准确率
    return train_loss_in_batch, train_acc_in_batch, train_loss_list, train_acc, test_loss_list, test_acc

# 测试函数（单独）
def test_epoch(net, data_loader, disp=False):
    # net.eval()
    if disp:
        print(net)
    test_batch_num = len(data_loader)
    total_loss = 0
    acc = 0
    sample_num = 0
    with torch.no_grad():
        for batch_idx, (data, target) in enumerate (data_loader):
            if len(data) != 32:
                continue
            # if batch_idx == 2:
            #     break
            tb1 = time.time()
            data, target = data.to(device), target.to(device)
            prediction = net(data)
            loss = criterion(prediction, target)
            total_loss += loss.item()
            sample_num += len(prediction)
            acc_num = (prediction.argmax(dim=1)==target).sum()
            acc += acc_num
            tb2 = time.time()
            print(f"\t|Test-in-batch:{batch_idx+1}/{len(data_loader)}, loss:{total_loss/sample_num}, acc:{acc/sample_num}, 耗时:{tb2-tb1}s")
    loss = total_loss/test_batch_num
    test_acc = acc/sample_num
    return loss, test_acc

# 小批量数据，减少GPU压力
train_loader16 = DataLoader(dataset=train_data, shuffle=True, batch_size=16)
test_loader16 = DataLoader(dataset=test_data, shuffle=True, batch_size=16)

# 定义画图函数
import matplotlib.pyplot as plt
def plot_batching(train_loss, train_acc):
    plt.figure(1)
    plt.xlabel('batch')
    plt.ylabel('loss')
    plt.title('Loss-Rate')
    # plt.plot([i for i in range(len(train_loss))], train_loss[i], 'b-', label=u'train_loss')
    mylist = []
    for i in range(len(train_loss)):
        mylist.append(train_loss[i].detach().numpy())
    plt.plot([i for i in range(len(train_loss))], mylist, 'b-', label=u'train_loss')
    plt.legend() 
    
    plt.figure(2)
    plt.xlabel("batch")  
    plt.ylabel("Acc")  
    plt.title("Accuracy")  
    plt.plot([i for i in range(len(train_acc))], train_acc, 'r-', label=u'train_acc')
    plt.legend() 

def plot_learning(train_loss, train_acc, test_loss, test_acc):
    plt.figure(1)
    plt.xlabel('epoch')
    plt.ylabel('loss')
    plt.title('Loss-Rate')
    plt.plot([i for i in range(len(train_loss))], train_loss, 'b-', label=u'train_loss')
    plt.legend() 
    plt.plot([i for i in range(len(test_loss))], test_loss, 'r-', label=u'test_loss')
    plt.legend() 
    
    plt.figure(2)
    plt.xlabel("epoch")  
    plt.ylabel("Acc")  
    plt.title("Accuracy")  
    plt.plot([i for i in range(len(train_acc))], train_acc, 'b-', label=u'train_acc')
    plt.legend() 
    plt.plot([i for i in range(len(test_acc))], test_acc, 'r-', label=u'test_acc')
    plt.legend()  

    plt.show()

# 手动实现
torch.cuda.empty_cache()
net11 = myCNN(3).to(device)
train_l_111, train_acc_111, train_l_112, train_acc_112, test_l11, test_acc11 = train_with_test(
    net11, train_loader, test_loader, batch_size=32, epochs=1, lr=0.01, optimizer=None, disp=True, skip=True)

手动实现卷积的结果

# 图表展示以batch为单位的训练结果
plot_batching(train_l_111, train_acc_111)

# nn实现卷积
torch.cuda.empty_cache()
net12 = nnCNN(3).to(device)
train_l_121, train_acc_121, train_l_122, train_acc_122, test_l12, test_acc12 = train_with_test(
    net12, train_loader, test_loader, epochs=10, lr=0.001)

nn实现卷积的结果

plot_learning(train_l_122, train_acc_122, test_l12, test_acc12)

探究超参数对CNN的影响

# 修改卷积层数
# 只用一层卷积
class nnCNNof1(nn.Module):
    def __init__(self, num_classes):
        super(nnCNNof1,self).__init__()
        # 三层卷积
        self.conv = nn.Sequential(
            # 这里设置了填充，因为图片大小为 200*200，运算过程出现了小数，这里是考虑不周到的地方
            nn.Conv2d(in_channels=3,out_channels=32,kernel_size=3,stride=1,padding=1),
            nn.BatchNorm2d(32),
            nn.ReLU(inplace=True),
        )
        self.fc = nn.Linear(32,num_classes)
    def forward(self,X):
        out= self.conv(X)
        out = F.avg_pool2d(out, kernel_size=out.size()[2:])
        out = out.view(out.size(0), -1)
        out = self.fc(out)
        return out
        
torch.cuda.empty_cache()
net13 = nnCNNof1(3).to(device)
train_l_131, train_acc_131, train_l_132, train_acc_132, test_l13, test_acc13 = train_with_test(
    net13, train_loader, test_loader, epochs=10, lr=lr)

# 作图对比
plot_learning(train_l_122, train_acc_122, test_l12, test_acc12)
plot_learning(train_l_132, train_acc_132, test_l13, test_acc13)

# 修改学习率
lr12 = 0.01
# lr = 0.001
torch.cuda.empty_cache()
net14 = nnCNN(3).to(device)
train_l_141, train_acc_141, train_l_142, train_acc_142, test_l14, test_acc14 = train_with_test(
    net14, train_loader, test_loader, epochs=10, lr=lr12)

# 作图对比
plot_learning(train_l_122, train_acc_122, test_l12, test_acc12)
plot_learning(train_l_142, train_acc_142, test_l14, test_acc14)

小结

1. 实验一中我将一层卷积与三层卷积进行了对比，前者loss下降的很慢，且预测正确率明显低于三层卷积，说明增加模型层数可以有助于获取更多、更高级别的特征表示 ，从而提高模型的预测能力；深度不够的模型，参数更新很慢 ，性能也不尽人意；模型深度提升三倍，训练时间也提升到接近三倍，似乎说明在本问题中模型深度与训练时间成正比。
2. 我将三层卷积模型的学习率由0.001提升至0.01，损失率得到更大幅度的下降 且仍呈圆弧状变化，说明该学习率是可被接纳的优秀学习率，初始0.001的学习率有些保守了；但从正确率来看，lr=0.01的曲线趋于平缓，似乎很难再单从学习率调整以达到更好的模型表现

二、空洞卷积实验

2.1 任务内容

1. 用torch.nn实现空洞卷积，要求dilation满足HDC条件（如1,2,5）且要 堆叠多层并在至少一个数据集上进行实验，从训练时间、预测精度、Loss
   变化等角度分析实验结果（最好使用图表展示）
2. 将空洞卷积模型的实验结果与卷积模型的结果进行分析比对，训练时间、 预测精度、Loss变化等角度分析
3. 不同超参数的对比分析（包括卷积层数、卷积核大小、不同dilation的选择， batchsize、lr等）选其中至少1-2个进行分析（选做）
   ）

2.2 任务思路及代码

# nn实现空洞卷积  
class nnDCNN(nn.Module):  
    def __init__(self,num_classes):  
        super(nnDCNN,self).__init__()  
        # 三层卷积
        self.conv=nn.Sequential(  
                # 添加padding，否则出现小数，下次一定要把图片缩放成2的幂
	            nn.Conv2d(in_channels=3,out_channels=32,kernel_size=3,stride=1,padding=1,dilation=1),  
	            nn.BatchNorm2d(32),  
	            nn.ReLU(inplace=True),  
	            nn.Conv2d(in_channels=32, out_channels=64, kernel_size=3, stride=1, padding=2,dilation=2),  
	            nn.BatchNorm2d(64),  
	            nn.ReLU(inplace=True),  
	            nn.Conv2d(in_channels=64, out_channels=128, kernel_size=3, stride=1, padding=4,dilation=5),  
	            nn.BatchNorm2d(128),  
	            nn.ReLU(inplace=True),  
	        )
        #输出层,将通道数变为分类数量  
        self.fc = nn.Linear(128,num_classes)  
    def forward(self,x):  
        out = self.conv(x)  
        out = F.avg_pool2d(out, kernel_size=out.size()[2:])  
        out = out.squeeze()  
        out = self.fc(out)  
        return out 

torch.cuda.empty_cache()
net21 = nnDCNN(num_classes=3).to(device)
train_l_211, train_acc_211, train_l_212, train_acc_212, test_l21, test_acc21 = train_with_test(
    net21, train_loader, test_loader, epochs=10, lr=0.001)

与CNN进行比对

plot_learning(train_l_212, train_acc_212, test_l21, test_acc21)
plot_learning(train_l_122, train_acc_122, test_l12, test_acc12)

探究超参数

# 修改层数
class nnDCNNof6(nn.Module):  
    def __init__(self, num_classes):  
        super(nnDCNNof6, self).__init__()  
        # 六层卷积
        self.conv = nn.Sequential(  
            nn.Conv2d(in_channels=3, out_channels=32, kernel_size=3, stride=1, padding=1, dilation=1),  
            nn.BatchNorm2d(32),  
            nn.ReLU(inplace=True),  
            nn.Conv2d(in_channels=32, out_channels=64, kernel_size=3, stride=1, padding=2, dilation=2),  
            nn.BatchNorm2d(64),  
            nn.ReLU(inplace=True),  
            nn.Conv2d(in_channels=64, out_channels=128, kernel_size=3, stride=1, padding=4, dilation=5),  
            nn.BatchNorm2d(128),  
            nn.ReLU(inplace=True),
            nn.Conv2d(in_channels=128, out_channels=256, kernel_size=3, stride=1, padding=8, dilation=10),  
            nn.BatchNorm2d(256),  
            nn.ReLU(inplace=True),
            nn.Conv2d(in_channels=256, out_channels=512, kernel_size=3, stride=1, padding=16, dilation=15),  
            nn.BatchNorm2d(512),  
            nn.ReLU(inplace=True),
            nn.Conv2d(in_channels=512, out_channels=1024, kernel_size=3, stride=1, padding=32, dilation=20),  
            nn.BatchNorm2d(1024),  
            nn.ReLU(inplace=True),
            nn.Conv2d(in_channels=1024, out_channels=2048, kernel_size=3, stride=1, padding=64, dilation=25),  
            nn.BatchNorm2d(2048),  
            nn.ReLU(inplace=True),
        )
        # 输出层，将通道数变为分类数量  
        self.fc = nn.Linear(2048, num_classes)  
        
    def forward(self, x):  
        out = self.conv(x)  
        out = F.avg_pool2d(out, kernel_size=out.size()[2:])  
        out = out.squeeze()  
        out = self.fc(out)  
        return out
        
torch.cuda.empty_cache()
net22 = nnDCNNof6(num_classes=3).to(device)
train_l_221, train_acc_221, train_l_222, train_acc_222, test_l22, test_acc22 = train_with_test(
    net22, train_loader, test_loader, epochs=10, lr=0.001)

# 作图比对
plot_learning(train_l_212, train_acc_212, test_l21, test_acc21)
plot_learning(train_l_222, train_acc_222, test_l22, test_acc22)

# 修改batch_size
torch.cuda.empty_cache()
net23 = nnDCNN(num_classes=3).to(device)
train_l_231, train_acc_231, train_l_232, train_acc_232, test_l23, test_acc23 = train_with_test(
    net23, train_loader16, test_loader16,batch_size=16, epochs=10, lr=0.001)

# 作图比对
plot_learning(train_l_212, train_acc_212, test_l21, test_acc21)
plot_learning(train_l_232, train_acc_232, test_l23, test_acc23)

小结

1. 空洞卷积和普通卷积的基本操作相同，都是通过卷积核与输入进行卷积操作。但它具有的扩展感受野、共享参数等性质，使得网络能更好地捕捉样本中的信息 ，因此获得了更好的正确率；空洞卷积的稀疏性也使得它比普通卷积的训练更快。
2. 在超参数实验中，我大胆尝试了将空洞卷积的模型深度翻倍：这造成了严重后果，我的电脑的GPU（显存16GB）根本无法负担这样的训练任务，说明模型深度的增加不仅会加大时间开销，更会造成GPU空间的更大占用，并增大算力负担；模型深度每增大k倍，造成的时间空间开销会增大p倍，p大于等于k。
3. 结果上来看，小批量的训练（74.87s）要慢于 大批量的训练（66.99s），但小批量的性能略微更优，因为它可以更频繁地更新模型参数，提供更多的随机性，对模型的泛化性能更有益。

三、残差网络实验

3.1 任务内容

实现给定结构的残差网络，在 至少一个数据集上进行实验， 从训练时间、预测精度、Loss 变化等角度分析实验结果（最

好使用图表展示）

3.2 任务思路及代码

class ResBlock(nn.Module):
    def __init__(self, in_channels, out_channels, stride=[1, 1], padding=1):
        super(ResBlock, self).__init__()
        self.layer = nn.Sequential(
            nn.Conv2d(in_channels, out_channels, kernel_size=3, stride=stride[0], padding=padding, bias=False),
            nn.BatchNorm2d(out_channels),
            nn.ReLU(inplace=True),
            nn.Conv2d(out_channels, out_channels, kernel_size=3, stride=stride[1], padding=padding, bias=False),
            nn.BatchNorm2d(out_channels)
        )

        self.shortcut = nn.Sequential()
        if stride[0] != 1 or in_channels != out_channels:
            self.shortcut = nn.Sequential(
                nn.Conv2d(in_channels, out_channels, kernel_size=1, stride=stride[0], bias=False),
                nn.BatchNorm2d(out_channels)
            )

    def forward(self, x):
        out = self.layer(x)
        shortcut = self.shortcut(x)
        if shortcut.size(1) != out.size(1):
            shortcut = F.pad(shortcut, (0, 0, 0, 0, 0, out.size(1) - shortcut.size(1)))
        out += shortcut
        out = F.relu(out)
        return out

class nnResNet(nn.Module):
    def __init__(self, num_classes=3) -> None:
        super(nnResNet, self).__init__()
        self.in_channels = 64

        self.conv1 = nn.Sequential(
            nn.Conv2d(3, 64, kernel_size=3, stride=1, padding=1, bias=False),
            nn.BatchNorm2d(64)
        )

        self.conv2 = self.set_layer(64, [[1, 1], [1, 1]])
        self.conv3 = self.set_layer(128, [[2, 1], [1, 1]])  
        self.conv4 = self.set_layer(256, [[2, 1], [1, 1]])  
        self.conv5 = self.set_layer(512, [[2, 1], [1, 1]])  
        self.avgpool = nn.AdaptiveAvgPool2d((1, 1))
        self.fc = nn.Sequential(
            nn.Linear(512, 256),
            nn.Linear(256, 128),
            nn.Linear(128, num_classes)
        )

    def set_layer(self, out_channels, strides):
        layers = []
        for stride in strides:
            layers.append(BasicBlock(self.in_channels, out_channels, stride))
            self.in_channels = out_channels
        return nn.Sequential(*layers)

    # 图片的大小为 200*200
    def forward(self, x):
        out = self.conv1(x)  # [32, 64, 200, 200]
        out = self.conv2(out)  # [32, 64, 200, 200]
        out = self.conv3(out)  # [32, 128, 100, 100]
        out = self.conv4(out)  # [32, 256, 50, 50]
        out = self.conv5(out)  # [32, 512, 25, 25]
        out = F.avg_pool2d(out, 25)  # [32, 512, 1, 1]
        out = out.squeeze()  # [32, 512]
        out = self.fc(out)
        return out

torch.cuda.empty_cache()
net31=nnResNet(num_classes=3).to(device)
train_l_311, train_acc_311, train_l_312, train_acc_312, test_l31, test_acc31 = train_with_test(
    net31, train_loader16, test_loader16, batch_size=16, epochs=10, lr=0.001, disp=True, skip=True)

# 绘制训练过程
plot_learning(train_l_312, train_acc_312, test_l31, test_acc31)

小结

1. 从训练结果来看，首先，由loss曲线，知本次训练的学习率过低，应使它接近于一个凹函数。
2. 其次，从正确率来看，残差模型达到了本次实验的最高正确度（>0.8）。
3. 从训练时间来看，残差网络的效率也很高，并没有比卷积和空洞卷积慢出很多；而残差网络的深度远远高于卷积网络，说明它具有更强的学习能力，能够学习更复杂的特征。
4. test_acc与train_acc平齐甚至更高，说明模型没有过拟合，残差网络具有更优异的优化和收敛性质。

实验总结

首先，本次实验学习了卷积、空洞卷积和残差网络三种模型，掌握了手动实现它们的训练过程，了解了它们的性质和优势。

其次，实验中有很多模型训练的地方值得优化，例如处理数据集图像时索性取最大值，将每张图片都缩放至200*200，这一点造成了维数降低时出现了小数，通过引入padding解决了这一问题。更加妥善的做法是采用2的幂，而不是随便一个数字。

最后，使用超参数的能力有所提升，包括对batch、学习率和模型深度的理解，增加了对机器学习实践的经验。