pytorch-构建卷积神经网络

构建卷积神经网络

  • 卷积网络中的输入和层与传统神经网络有些区别,需重新设计,训练模块基本一致
    import torch
    import torch.nn as nn
    import torch.optim as optim
    import torch.nn.functional as F
    from torchvision import datasets,transforms 
    import matplotlib.pyplot as plt
    import numpy as np
    %matplotlib inline

    首先读取数据

  • 分别构建训练集和测试集(验证集)
  • DataLoader来迭代取数据
    # 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)

    卷积网络模块构建

  • 一般卷积层,relu层,池化层可以写成一个套餐
  • 注意卷积最后结果还是一个特征图,需要把图转换成向量才能做分类或者回归任务
    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

    准确率作为评估标准

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

    训练网络模型

    # 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%
    

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