利用神经网络完成对手写数字进行识别

我不是女神ヾ 2022-12-21 04:55 146阅读 0赞

# 利用神经网络完成对手写数字进行识别 #

*  网络结构
    
    ![12078205661bebb59b5e118599fe16e9.png][]

> 两个隐藏层  
> 每层激活函数为Relu  
> 数据集：mnist

### 1. 准备数据 ###

import os
    import numpy as np
    import matplotlib.pyplot as plt
    import torch
    # 导入 pytorch 内置的 mnist 数据
    from torchvision.datasets import mnist
    # 导入预处理模块
    import torchvision.transforms as transforms
    from torch.utils.data import DataLoader
    # 导入nn及优化器
    import torch.nn.functional as F
    import torch.optim as optim
    from torch import nn

### 2. 定义一些超参数 ###

# 定义一些超参数
    train_batch_size = 64
    test_batch_size = 128
    learning_rate = 0.01
    num_epoches = 20
    lr = 0.01
    momentum = 0.5

### 3. 下载数据并对数据进行预处理 ###

# 定义预处理函数，这些预处理依次放在Compose函数中。
    transform = transforms.Compose(
        [transforms.ToTensor(), transforms.Normalize([0.5], [0.5])])
    
    # 判断是否需要从网络下载数据集
    is_downloda = True
    if os.path.exists('./data/MNIST'):
        is_downloda = False
    # 下载数据，并对数据进行预处理
    train_dataset = mnist.MNIST(
        './data', train=True, transform=transform, download=is_downloda)
    test_dataset = mnist.MNIST('./data', train=False, transform=transform)
    
    # dataloader是一个可迭代对象，可以使用迭代器一样使用。
    train_loader = DataLoader(
        train_dataset, batch_size=train_batch_size, shuffle=True)
    test_loader = DataLoader(
        test_dataset, batch_size=test_batch_size, shuffle=False)

*  Normalize(\[0.5\], \[0.5\])对张量进行归一化，这里两个0.5分别表示对张量进行归一化的全局平均值和方差。因图像是灰色的只有一个通道，如果有多个通道，需要有多个数字，如三个通道，应该是Normalize(\[m1,m2,m3\], \[n1,n2,n3\])
 *  用DataLoader得到生成器，可节省内存。

### 4. 可视化源数据 ###

examples = enumerate(test_loader)
    # enumerate() 函数用于将一个可遍历的数据对象(如列表、元组或字符串)组合为一个索引序列，同时列出数据和数据下标。
    batch_idx, (example_data, example_targets) = next(examples)
    # next() 返回迭代器的下一个项目。
    
    fig = plt.figure()
    for i in range(6):
        plt.subplot(2, 3, i+1)
        plt.tight_layout()
        plt.imshow(example_data[i][0], cmap='gray', interpolation='none')
        plt.title("Ground Truth: {}".format(example_targets[i]))
        # 关闭x,y轴显示
        plt.xticks([])
        plt.yticks([])

![png][]

### 5. 构建模型 ###

#### 5.1 构建网络 ####

class Net(nn.Module):
        """ 使用sequential构建网络，Sequential()函数的功能是将网络的层组合到一起 """
    
        def __init__(self, in_dim, n_hidden_1, n_hidden_2, out_dim):
            super(Net, self).__init__()
            self.layer1 = nn.Sequential(
                nn.Linear(in_dim, n_hidden_1), nn.BatchNorm1d(n_hidden_1))
            self.layer2 = nn.Sequential(
                nn.Linear(n_hidden_1, n_hidden_2), nn.BatchNorm1d(n_hidden_2))
            self.layer3 = nn.Sequential(nn.Linear(n_hidden_2, out_dim))
    
        def forward(self, x):
            x = F.relu(self.layer1(x))
            x = F.relu(self.layer2(x))
            x = self.layer3(x)
            return x

#### 5.2 实例化网络 ####

# 检测是否有可用的GPU，有则使用，否则使用CPU
    print("GPU是否可用", torch.cuda.is_available())
    device = torch.device("cuda:0" if torch.cuda.is_available() else "cpu")
    # 实例化网络
    model = Net(28 * 28, 300, 100, 10)
    # 输出10维（10个数字）
    model.to(device)
    
    # 定义损失函数和优化器
    criterion = nn.CrossEntropyLoss()
    optimizer = optim.SGD(model.parameters(), lr=lr, momentum=momentum)

GPU是否可用 False

### 6. 训练模型 ###

#### 6.1 训练模型 ####

# 开始训练
    losses = []
    acces = []
    eval_losses = []
    eval_acces = []
    
    
    for epoch in range(num_epoches):
        train_loss = 0
        train_acc = 0
        model.train()
        # 动态修改参数学习率
        if epoch % 5 == 0:
            optimizer.param_groups[0]['lr'] *= 0.1
        for img, label in train_loader:
            img = img.to(device)
            label = label.to(device)
            img = img.view(img.size(0), -1)  # 展成1维
            # 前向传播
            out = model(img)  # 传入参数，自动执行forward函数
            loss = criterion(out, label)
    
            optimizer.zero_grad()  # 梯度清零
            # 反向传播
            # 缺省情况下，梯度是累加的，在梯度反向传播之前，需要梯度清零
            loss.backward()
            optimizer.step()  # 基于当前梯度，更新参数
            # 记录误差
            train_loss += loss.item()
            # 计算分类的准确率
            _, pred = out.max(1)  # 找出张量out最大值对应索引作为预测值
            num_correct = (pred == label).sum().item()
            acc = num_correct / img.shape[0]
            train_acc += acc
    
        losses.append(train_loss / len(train_loader))
        acces.append(train_acc / len(train_loader))
    
        # 在测试集上检验效果
        eval_loss = 0
        eval_acc = 0
        # 将模型改为预测模式
        model.eval()
        for img, label in test_loader:
            img = img.to(device)
            label = label.to(device)
            img = img.view(img.size(0), -1)
            # 前向传播
            out = model(img)
            loss = criterion(out, label)
            # 记录误差
            eval_loss += loss.item()
            # 记录准确率
            _, pred = out.max(1)
            num_correct = (pred == label).sum().item()
            acc = num_correct / img.shape[0]
            eval_acc += acc
    
        eval_losses.append(eval_loss / len(test_loader))
        eval_acces.append(eval_acc / len(test_loader))
    
        print('epoch: {}, Train Loss: {:.4f}, Train Acc: {:.4f}, Test Loss: {:.4f}, Test Acc: {:.4f}'
              .format(epoch, train_loss / len(train_loader), train_acc / len(train_loader),
                      eval_loss / len(test_loader), eval_acc / len(test_loader)))

epoch: 0, Train Loss: 1.0274, Train Acc: 0.7921, Test Loss: 0.5553, Test Acc: 0.9008
    epoch: 1, Train Loss: 0.4833, Train Acc: 0.8995, Test Loss: 0.3530, Test Acc: 0.9259
    epoch: 2, Train Loss: 0.3504, Train Acc: 0.9187, Test Loss: 0.2769, Test Acc: 0.9384
    epoch: 3, Train Loss: 0.2838, Train Acc: 0.9328, Test Loss: 0.2301, Test Acc: 0.9483
    epoch: 4, Train Loss: 0.2431, Train Acc: 0.9408, Test Loss: 0.1980, Test Acc: 0.9530
    epoch: 5, Train Loss: 0.2202, Train Acc: 0.9463, Test Loss: 0.1964, Test Acc: 0.9534
    epoch: 6, Train Loss: 0.2188, Train Acc: 0.9464, Test Loss: 0.1913, Test Acc: 0.9537
    epoch: 7, Train Loss: 0.2159, Train Acc: 0.9471, Test Loss: 0.1882, Test Acc: 0.9551
    epoch: 8, Train Loss: 0.2131, Train Acc: 0.9487, Test Loss: 0.1869, Test Acc: 0.9540
    epoch: 9, Train Loss: 0.2107, Train Acc: 0.9490, Test Loss: 0.1835, Test Acc: 0.9559
    epoch: 10, Train Loss: 0.2081, Train Acc: 0.9500, Test Loss: 0.1846, Test Acc: 0.9552
    epoch: 11, Train Loss: 0.2090, Train Acc: 0.9492, Test Loss: 0.1855, Test Acc: 0.9558
    epoch: 12, Train Loss: 0.2091, Train Acc: 0.9483, Test Loss: 0.1841, Test Acc: 0.9558
    epoch: 13, Train Loss: 0.2076, Train Acc: 0.9493, Test Loss: 0.1871, Test Acc: 0.9544
    epoch: 14, Train Loss: 0.2066, Train Acc: 0.9491, Test Loss: 0.1833, Test Acc: 0.9562
    epoch: 15, Train Loss: 0.2086, Train Acc: 0.9491, Test Loss: 0.1837, Test Acc: 0.9560
    epoch: 16, Train Loss: 0.2074, Train Acc: 0.9496, Test Loss: 0.1827, Test Acc: 0.9559
    epoch: 17, Train Loss: 0.2076, Train Acc: 0.9488, Test Loss: 0.1835, Test Acc: 0.9559
    epoch: 18, Train Loss: 0.2076, Train Acc: 0.9494, Test Loss: 0.1845, Test Acc: 0.9558
    epoch: 19, Train Loss: 0.2074, Train Acc: 0.9497, Test Loss: 0.1844, Test Acc: 0.9551

#### 6.2 可视化训练及测试损失值 ####

plt.title('train loss')
    plt.subplot(1,2,1)
    plt.plot(np.arange(len(losses)), losses)
    plt.legend(['Train Loss'], loc='upper right')
    
    plt.subplot(1,2,2)
    plt.title('train acces')
    plt.plot(np.arange(len(acces)),acces,color='red', label='acces')
    plt.legend(['Train acces'], loc='upper right')

<matplotlib.legend.Legend at 0x7fb0dd687ac0>

![png][png 1]

[12078205661bebb59b5e118599fe16e9.png]: /images/20221120/24c83f31b0e448c3af13e50fe625767e.png
[png]: /images/20221120/6d01f88dca3e433c926954747bfd6d19.png
[png 1]: /images/20221120/cbe674e47ef34eba92828588dd8486da.png