Use of pytorch: Convolutional Neural Network Module

1.读取数据

• 分别构建训练集和测试集（验证集）
• DataLoader来迭代取数据
• 使用transforms将数据转换为tensor格式

# 定义超参数 
input_size = 28  #图像的总尺寸28*28
num_classes = 10  #标签的种类数
num_epochs = 3  #训练的总循环周期
batch_size = 64  #一个撮（批次）的大小,64张图片

# 训练集
train_dataset = datasets.MNIST(root='./data',  
                            train=True,   
                            transform=transforms.ToTensor(),  
                            download=True) 

# 测试集
test_dataset = datasets.MNIST(root='./data', 
                           train=False, 
                           transform=transforms.ToTensor())

# 构建batch数据
train_loader = torch.utils.data.DataLoader(dataset=train_dataset, 
                                           batch_size=batch_size, 
                                           shuffle=True)
test_loader = torch.utils.data.DataLoader(dataset=test_dataset, 
                                           batch_size=batch_size, 
                                           shuffle=True)

 

1.Convolutional Neural Network Module

pytorch与tensorflow 2相比,pytorch更注重过程,pytochThe convolution module needs to specify the number of input channels and the number of output channels,The total number of parameters of the convolution kernel is 卷积核K x 卷积核K x 输入通道数 x 输出通道数,卷积模块padding也需要自己计算,如果希望卷积后大小跟原来一样,需要设置padding=(kernel_size-1)/2 if stride=1,pytochWhen calculating the feature size of the next layer,The principle of rounding down is used,另外pytorch特征维度为batch*channels*h*w,channels在第二维度.

class CNN(nn.Module):
    def __init__(self):
        super(CNN, self).__init__()
        self.conv1 = nn.Sequential(         # 输入大小 (1, 28, 28)
            nn.Conv2d(
                in_channels=1,              # 灰度图
                out_channels=16,            # 要得到几多少个特征图
                kernel_size=5,              # 卷积核大小
                stride=1,                   # 步长
                padding=2,                  # 如果希望卷积后大小跟原来一样,需要设置padding=(kernel_size-1)/2 if stride=1
            ),                              # 输出的特征图为 (16, 28, 28)
            nn.ReLU(),                      # relu层
            nn.MaxPool2d(kernel_size=2),    # 进行池化操作（2x2 区域）, 输出结果为： (16, 14, 14)
        )
        self.conv2 = nn.Sequential(         # 下一个套餐的输入 (16, 14, 14)
            nn.Conv2d(16, 32, 5, 1, 2),     # 输出 (32, 14, 14)
            nn.ReLU(),                      # relu层
            nn.Conv2d(32, 32, 5, 1, 2),
            nn.ReLU(),
            nn.MaxPool2d(2),                # 输出 (32, 7, 7)
        )
        
        self.conv3 = nn.Sequential(         # 下一个套餐的输入 (16, 14, 14)
            nn.Conv2d(32, 64, 5, 1, 2),     # 输出 (32, 14, 14)
            nn.ReLU(),             # 输出 (32, 7, 7)
        )
        
        self.out = nn.Linear(64 * 7 * 7, 10)   # 全连接层得到的结果

    def forward(self, x):
        x = self.conv1(x)
        x = self.conv2(x)
        x = self.conv3(x)
        x = x.view(x.size(0), -1)           # flatten操作,结果为：(batch_size, 32 * 7 * 7)
        output = self.out(x)
        return output

3.训练网络模型 

Define accuracy as a validation set evaluation metric 

def accuracy(predictions, labels):
    pred = torch.max(predictions.data, 1)[1] 
    rights = pred.eq(labels.data.view_as(pred)).sum() 
    return rights, len(labels) 

 

# 实例化
net = CNN() 
#损失函数
criterion = nn.CrossEntropyLoss() 
#优化器
optimizer = optim.Adam(net.parameters(), lr=0.001) #定义优化器,普通的随机梯度下降算法

#开始训练循环
for epoch in range(num_epochs):
    #当前epoch的结果保存下来
    train_rights = [] 
    
    for batch_idx, (data, target) in enumerate(train_loader):  #针对容器中的每一个批进行循环
        net.train()                             
        output = net(data) 
        loss = criterion(output, target) 
        optimizer.zero_grad() 
        loss.backward() 
        optimizer.step() 
        right = accuracy(output, target) 
        train_rights.append(right) 

    
        if batch_idx % 100 == 0: 
            
            net.eval() 
            val_rights = [] 
            
            for (data, target) in test_loader:
                output = net(data) 
                right = accuracy(output, target) 
                val_rights.append(right)
                
            #准确率计算
            train_r = (sum([tup[0] for tup in train_rights]), sum([tup[1] for tup in train_rights]))
            val_r = (sum([tup[0] for tup in val_rights]), sum([tup[1] for tup in val_rights]))

            print('当前epoch: {} [{}/{} ({:.0f}%)]\t损失: {:.6f}\t训练集准确率: {:.2f}%\t测试集正确率: {:.2f}%'.format(
                epoch, batch_idx * batch_size, len(train_loader.dataset),
                100. * batch_idx / len(train_loader), 
                loss.data, 
                100. * train_r[0].numpy() / train_r[1], 
                100. * val_r[0].numpy() / val_r[1]))

当前epoch: 0 [0/60000 (0%)]	损失: 2.300918	训练集准确率: 10.94%	测试集正确率: 10.10%
当前epoch: 0 [6400/60000 (11%)]	损失: 0.204191	训练集准确率: 78.06%	测试集正确率: 93.31%
当前epoch: 0 [12800/60000 (21%)]	损失: 0.039503	训练集准确率: 86.51%	测试集正确率: 96.69%
当前epoch: 0 [19200/60000 (32%)]	损失: 0.057866	训练集准确率: 89.93%	测试集正确率: 97.54%
当前epoch: 0 [25600/60000 (43%)]	损失: 0.069566	训练集准确率: 91.68%	测试集正确率: 97.68%
当前epoch: 0 [32000/60000 (53%)]	损失: 0.228793	训练集准确率: 92.85%	测试集正确率: 98.18%
当前epoch: 0 [38400/60000 (64%)]	损失: 0.111003	训练集准确率: 93.72%	测试集正确率: 98.16%
当前epoch: 0 [44800/60000 (75%)]	损失: 0.110226	训练集准确率: 94.28%	测试集正确率: 98.44%
当前epoch: 0 [51200/60000 (85%)]	损失: 0.014538	训练集准确率: 94.78%	测试集正确率: 98.60%
当前epoch: 0 [57600/60000 (96%)]	损失: 0.051019	训练集准确率: 95.14%	测试集正确率: 98.45%
当前epoch: 1 [0/60000 (0%)]	损失: 0.036383	训练集准确率: 98.44%	测试集正确率: 98.68%
当前epoch: 1 [6400/60000 (11%)]	损失: 0.088116	训练集准确率: 98.50%	测试集正确率: 98.37%
当前epoch: 1 [12800/60000 (21%)]	损失: 0.120306	训练集准确率: 98.59%	测试集正确率: 98.97%
当前epoch: 1 [19200/60000 (32%)]	损失: 0.030676	训练集准确率: 98.63%	测试集正确率: 98.83%
当前epoch: 1 [25600/60000 (43%)]	损失: 0.068475	训练集准确率: 98.59%	测试集正确率: 98.87%
当前epoch: 1 [32000/60000 (53%)]	损失: 0.033244	训练集准确率: 98.62%	测试集正确率: 99.03%
当前epoch: 1 [38400/60000 (64%)]	损失: 0.024162	训练集准确率: 98.67%	测试集正确率: 98.81%
当前epoch: 1 [44800/60000 (75%)]	损失: 0.006713	训练集准确率: 98.69%	测试集正确率: 98.17%
当前epoch: 1 [51200/60000 (85%)]	损失: 0.009284	训练集准确率: 98.69%	测试集正确率: 98.97%
当前epoch: 1 [57600/60000 (96%)]	损失: 0.036536	训练集准确率: 98.68%	测试集正确率: 98.97%
当前epoch: 2 [0/60000 (0%)]	损失: 0.125235	训练集准确率: 98.44%	测试集正确率: 98.73%
当前epoch: 2 [6400/60000 (11%)]	损失: 0.028075	训练集准确率: 99.13%	测试集正确率: 99.17%
当前epoch: 2 [12800/60000 (21%)]	损失: 0.029663	训练集准确率: 99.26%	测试集正确率: 98.39%
当前epoch: 2 [19200/60000 (32%)]	损失: 0.073855	训练集准确率: 99.20%	测试集正确率: 98.81%
当前epoch: 2 [25600/60000 (43%)]	损失: 0.018130	训练集准确率: 99.16%	测试集正确率: 99.09%
当前epoch: 2 [32000/60000 (53%)]	损失: 0.006968	训练集准确率: 99.15%	测试集正确率: 99.11%