DAY 40

# DAY 40 简单 CNN

知识回顾:

1. 数据增强

2. 卷积神经网络定义的写法

3. batch 归一化：调整一个批次的分布，常用与图像数据

4. 特征图：只有卷积操作输出的才叫特征图

5. 调度器：直接修改基础学习率

卷积操作常见流程如下：

- 输入 → 卷积层 → Batch 归一化层（可选）→ 池化层 → 激活函数 → 下一层

- Flatten → Dense (with Dropout, 可选) → Dense (Output)

作业：尝试手动修改不同的调度器和 CNN 的结构，观察训练的差异。

import torch import torch.nn as nn import torch.optim as optim import matplotlib.pyplot as plt from torch.utils.data import DataLoader from torchvision import datasets, transforms # ---------------------- 1. 数据准备 ---------------------- # 数据预处理（CIFAR-10） transform = transforms.Compose([ transforms.ToTensor(), transforms.Normalize((0.4914, 0.4822, 0.4465), (0.2023, 0.1994, 0.2010)) # CIFAR-10官方均值/标准差 ]) # 加载数据集 train_dataset = datasets.CIFAR10(root='./data', train=True, download=True, transform=transform) test_dataset = datasets.CIFAR10(root='./data', train=False, download=True, transform=transform) train_loader = DataLoader(train_dataset, batch_size=64, shuffle=True) test_loader = DataLoader(test_dataset, batch_size=64, shuffle=False) # 设备选择 device = torch.device("cuda" if torch.cuda.is_available() else "cpu") epochs = 20 # 统一训练轮次，保证对比公平 # ---------------------- 2. 定义不同的CNN结构 ---------------------- # 原CNN（对照组） class CNN_Base(nn.Module): def __init__(self): super(CNN_Base, self).__init__() # 卷积块1 self.conv1 = nn.Conv2d(3, 32, 3, padding=1) self.bn1 = nn.BatchNorm2d(32) self.relu1 = nn.ReLU() self.pool1 = nn.MaxPool2d(2) # 卷积块2 self.conv2 = nn.Conv2d(32, 64, 3, padding=1) self.bn2 = nn.BatchNorm2d(64) self.relu2 = nn.ReLU() self.pool2 = nn.MaxPool2d(2) # 卷积块3 self.conv3 = nn.Conv2d(64, 128, 3, padding=1) self.bn3 = nn.BatchNorm2d(128) self.relu3 = nn.ReLU() self.pool3 = nn.MaxPool2d(2) # 全连接层 self.fc1 = nn.Linear(128 * 4 * 4, 512) self.dropout = nn.Dropout(0.5) self.fc2 = nn.Linear(512, 10) def forward(self, x): x = self.pool1(self.relu1(self.bn1(self.conv1(x)))) x = self.pool2(self.relu2(self.bn2(self.conv2(x)))) x = self.pool3(self.relu3(self.bn3(self.conv3(x)))) x = x.view(-1, 128 * 4 * 4) x = self.dropout(self.relu3(self.fc1(x))) x = self.fc2(x) return x # 变体1：轻量化CNN（减少通道数、简化结构） class CNN_Light(nn.Module): def __init__(self): super(CNN_Light, self).__init__() # 卷积块1（通道数减半） self.conv1 = nn.Conv2d(3, 16, 3, padding=1) self.bn1 = nn.BatchNorm2d(16) self.relu1 = nn.ReLU() self.pool1 = nn.MaxPool2d(2) # 卷积块2（减少1个卷积块） self.conv2 = nn.Conv2d(16, 32, 3, padding=1) self.bn2 = nn.BatchNorm2d(32) self.relu2 = nn.ReLU() self.pool2 = nn.MaxPool2d(2) # 全连接层（神经元数减半） self.fc1 = nn.Linear(32 * 8 * 8, 256) # 尺寸：32×8×8（因少了1次池化） self.dropout = nn.Dropout(0.3) # 降低Dropout率 self.fc2 = nn.Linear(256, 10) def forward(self, x): x = self.pool1(self.relu1(self.bn1(self.conv1(x)))) # 尺寸：16×16×16 x = self.pool2(self.relu2(self.bn2(self.conv2(x)))) # 尺寸：32×8×8 x = x.view(-1, 32 * 8 * 8) x = self.dropout(self.relu1(self.fc1(x))) x = self.fc2(x) return x # 变体2：加深CNN（增加卷积块、提升通道数） class CNN_Deep(nn.Module): def __init__(self): super(CNN_Deep, self).__init__() # 卷积块1 self.conv1 = nn.Conv2d(3, 32, 3, padding=1) self.bn1 = nn.BatchNorm2d(32) self.relu1 = nn.ReLU() self.pool1 = nn.MaxPool2d(2) # 卷积块2 self.conv2 = nn.Conv2d(32, 64, 3, padding=1) self.bn2 = nn.BatchNorm2d(64) self.relu2 = nn.ReLU() self.pool2 = nn.MaxPool2d(2) # 卷积块3 self.conv3 = nn.Conv2d(64, 128, 3, padding=1) self.bn3 = nn.BatchNorm2d(128) self.relu3 = nn.ReLU() self.pool3 = nn.MaxPool2d(2) # 新增卷积块4 self.conv4 = nn.Conv2d(128, 256, 3, padding=1) self.bn4 = nn.BatchNorm2d(256) self.relu4 = nn.ReLU() self.pool4 = nn.MaxPool2d(2) # 新增池化 # 全连接层（适配新尺寸） self.fc1 = nn.Linear(256 * 2 * 2, 512) # 尺寸：256×2×2（多1次池化） self.dropout = nn.Dropout(0.5) self.fc2 = nn.Linear(512, 10) def forward(self, x): x = self.pool1(self.relu1(self.bn1(self.conv1(x)))) x = self.pool2(self.relu2(self.bn2(self.conv2(x)))) x = self.pool3(self.relu3(self.bn3(self.conv3(x)))) x = self.pool4(self.relu4(self.bn4(self.conv4(x)))) # 新增卷积块处理 x = x.view(-1, 256 * 2 * 2) x = self.dropout(self.relu3(self.fc1(x))) x = self.fc2(x) return x # ---------------------- 3. 训练函数 ---------------------- def train(model, train_loader, test_loader, criterion, optimizer, scheduler, device, epochs): model.train() all_iter_losses = [] iter_indices = [] train_acc_history = [] test_acc_history = [] train_loss_history = [] test_loss_history = [] for epoch in range(epochs): running_loss = 0.0 correct = 0 total = 0 for batch_idx, (data, target) in enumerate(train_loader): data, target = data.to(device), target.to(device) optimizer.zero_grad() output = model(data) loss = criterion(output, target) loss.backward() optimizer.step() # 记录损失 iter_loss = loss.item() all_iter_losses.append(iter_loss) iter_indices.append(epoch * len(train_loader) + batch_idx + 1) # 统计训练指标 running_loss += iter_loss _, predicted = output.max(1) total += target.size(0) correct += predicted.eq(target).sum().item() if (batch_idx + 1) % 100 == 0: print(f'Epoch: {epoch+1}/{epochs} | Batch: {batch_idx+1}/{len(train_loader)} ' f'| 单Batch损失: {iter_loss:.4f} | 累计平均损失: {running_loss/(batch_idx+1):.4f}') # 训练指标统计 epoch_train_loss = running_loss / len(train_loader) epoch_train_acc = 100. * correct / total train_acc_history.append(epoch_train_acc) train_loss_history.append(epoch_train_loss) # 测试阶段 model.eval() test_loss = 0 correct_test = 0 total_test = 0 with torch.no_grad(): for data, target in test_loader: data, target = data.to(device), target.to(device) output = model(data) test_loss += criterion(output, target).item() _, predicted = output.max(1) total_test += target.size(0) correct_test += predicted.eq(target).sum().item() epoch_test_loss = test_loss / len(test_loader) epoch_test_acc = 100. * correct_test / total_test test_acc_history.append(epoch_test_acc) test_loss_history.append(epoch_test_loss) # 更新学习率（不同调度器的step方式一致） scheduler.step(epoch_test_loss) print(f'Epoch {epoch+1}/{epochs} 完成 | 训练准确率: {epoch_train_acc:.2f}% | 测试准确率: {epoch_test_acc:.2f}%') # 绘图 plot_iter_losses(all_iter_losses, iter_indices) plot_epoch_metrics(train_acc_history, test_acc_history, train_loss_history, test_loss_history) return epoch_test_acc # ---------------------- 4. 绘图函数 ---------------------- def plot_iter_losses(losses, indices): plt.figure(figsize=(10, 4)) plt.plot(indices, losses, 'b-', alpha=0.7, label='Iteration Loss') plt.xlabel('Iteration（Batch序号）') plt.ylabel('损失值') plt.title('每个 Iteration 的训练损失') plt.legend() plt.grid(True) plt.tight_layout() plt.show() def plot_epoch_metrics(train_acc, test_acc, train_loss, test_loss): epochs = range(1, len(train_acc) + 1) plt.figure(figsize=(12, 4)) # 准确率 plt.subplot(1, 2, 1) plt.plot(epochs, train_acc, 'b-', label='训练准确率') plt.plot(epochs, test_acc, 'r-', label='测试准确率') plt.xlabel('Epoch') plt.ylabel('准确率 (%)') plt.title('训练和测试准确率') plt.legend() plt.grid(True) # 损失 plt.subplot(1, 2, 2) plt.plot(epochs, train_loss, 'b-', label='训练损失') plt.plot(epochs, test_loss, 'r-', label='测试损失') plt.xlabel('Epoch') plt.ylabel('损失值') plt.title('训练和测试损失') plt.legend() plt.grid(True) plt.tight_layout() plt.show() # ---------------------- 5. 多个对比实验 ---------------------- criterion = nn.CrossEntropyLoss() # 统一损失函数 # 实验1：原CNN + ReduceLROnPlateau（对照组） print("\n===== 实验1：原CNN + ReduceLROnPlateau =====") model1 = CNN_Base().to(device) optimizer1 = optim.Adam(model1.parameters(), lr=0.001) scheduler1 = optim.lr_scheduler.ReduceLROnPlateau(optimizer1, mode='min', patience=3, factor=0.5) acc1 = train(model1, train_loader, test_loader, criterion, optimizer1, scheduler1, device, epochs) # 实验2：原CNN + StepLR（仅改调度器） print("\n===== 实验2：原CNN + StepLR =====") model2 = CNN_Base().to(device) optimizer2 = optim.Adam(model2.parameters(), lr=0.001) scheduler2 = optim.lr_scheduler.StepLR(optimizer2, step_size=5, gamma=0.5) # 每5个epoch降50% acc2 = train(model2, train_loader, test_loader, criterion, optimizer2, scheduler2, device, epochs) # 实验3：轻量化CNN + ReduceLROnPlateau（仅改结构） print("\n===== 实验3：轻量化CNN + ReduceLROnPlateau =====") model3 = CNN_Light().to(device) optimizer3 = optim.Adam(model3.parameters(), lr=0.001) scheduler3 = optim.lr_scheduler.ReduceLROnPlateau(optimizer3, mode='min', patience=3, factor=0.5) acc3 = train(model3, train_loader, test_loader, criterion, optimizer3, scheduler3, device, epochs) # 实验4：加深CNN + CosineAnnealingLR（改结构+调度器） print("\n===== 实验4：加深CNN + CosineAnnealingLR =====") model4 = CNN_Deep().to(device) optimizer4 = optim.Adam(model4.parameters(), lr=0.001) scheduler4 = optim.lr_scheduler.CosineAnnealingLR(optimizer4, T_max=10) # 周期10个epoch acc4 = train(model4, train_loader, test_loader, criterion, optimizer4, scheduler4, device, epochs) # 打印最终结果对比 print("\n===== 所有实验最终测试准确率 =====") print(f"实验1（原CNN+ReduceLROnPlateau）：{acc1:.2f}%") print(f"实验2（原CNN+StepLR）：{acc2:.2f}%") print(f"实验3（轻量化CNN+ReduceLROnPlateau）：{acc3:.2f}%") print(f"实验4（加深CNN+CosineAnnealingLR）：{acc4:.2f}%")

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