基于PyTorch的CIFAR10小记

CIFAR-10数据集介绍

CIFAR-10数据集由10个类的60000个32x32彩色图像组成，每个类有6000个图像。有50000个训练图像和10000个测试图像。
数据集分为五个训练批次和一个测试批次，每个批次有10000个图像。测试批次包含来自每个类别的恰好1000个随机选择的图像。训练批次以随机顺序包含剩余图像，但一些训练批次可能包含来自一个类别的图像比另一个更多。总体来说，五个训练集之和包含来自每个类的正好5000张图像。
以下是数据集中的类，以及来自每个类的10个随机图像：

下载地址：http://www.cs.toronto.edu/~kriz/cifar-10-python.tar.gz

切入正题

这次实践主要参考PyTorch官方的教程https://pytorch.org/tutorials/beginner/blitz/cifar10_tutorial.html#sphx-glr-beginner-blitz-cifar10-tutorial-py，在此基础上进行一些修改，由于主要目的是了解PyTorch的编程方法，所以在数据集那里并没有从训练集中切分验证集出来，在训练时仅观察了loss的变化，最后使用测试集观察准确率。

关于数据集

CIFAR10的数据集可以通过torchvision进行下载，但是下载速度太慢，建议使用迅雷下载

开搞

导入基础包

import torch
import torchvision
import torchvision.transforms as transforms
import matplotlib.pyplot as plt
import numpy as np

# 设置一些参数
EPOCHS = 20
BATCH_SIZE = 512

创建数据集

# 创建一个转换器，将torchvision数据集的输出范围[0,1]转换为归一化范围的张量[-1,1]。
transform = transforms.Compose([
    transforms.ToTensor(),
    transforms.Normalize((0.5, 0.5, 0.5), (0.5, 0.5, 0.5))
])

# 创建训练集
# root -- 数据存放的目录
# train -- 明确是否是训练集
# download -- 是否需要下载
# transform -- 转换器，将数据集进行转换
trainset = torchvision.datasets.CIFAR10(
    root='./data',
    train=True,
    download=True,
    transform=transform
)

# 创建测试集
testset = torchvision.datasets.CIFAR10(
    root='./data',
    train=False,
    download=True,
    transform=transform
)

创建数据加载器

# 创建训练/测试加载器，
# trainset/testset -- 数据集
# batch_size -- 不解释
# shuffle -- 是否打乱顺序
trainloader = torch.utils.data.DataLoader(
    trainset, batch_size=BATCH_SIZE, shuffle=True)
testloader = torch.utils.data.DataLoader(
    testset, batch_size=BATCH_SIZE, shuffle=True)

# 类别标签
classes = ('plane', 'car', 'bird', 'cat',
           'deer', 'dog', 'frog', 'horse', 'ship', 'truck')

创建网络

我这里定义了两个CNN网络，分别保存在CNN_1.py和CNN_2.py文件中

CNN_1

# CNN_1.py
import torch

# 学习率
LR = 0.005

class Net(torch.nn.Module):
    """Some Information about Net"""

    def __init__(self):
        super(Net, self).__init__()
        self.conv1 = torch.nn.Sequential(
            torch.nn.Conv2d(3, 16, 3, padding=1),  # 3*32*32 -> 16*32*32
            torch.nn.ReLU(),
            torch.nn.MaxPool2d(2, 2)  # 16*32*32 -> 16*16*16
        )
        self.conv2 = torch.nn.Sequential(
            torch.nn.Conv2d(16, 32, 3, padding=1),  # 16*16*16 -> 32*16*16
            torch.nn.ReLU(),
            torch.nn.MaxPool2d(2, 2)  # 32*16*16 -> 32*8*8
        )
        self.conv3 = torch.nn.Sequential(
            torch.nn.Conv2d(32, 64, 3, padding=1),  # 32*8*8 -> 64*8*8
            torch.nn.ReLU(),
            torch.nn.MaxPool2d(2, 2)  # 64*8*8 -> 64*4*4
        )
        self.fc1 = torch.nn.Sequential(
            torch.nn.Linear(64*4*4, 32),
            torch.nn.ReLU(),
            # torch.nn.Dropout()
        )
        self.fc2 = torch.nn.Linear(32, 10)

    def forward(self, x):
        x = self.conv1(x)
        x = self.conv2(x)
        x = self.conv3(x)
        x = x.view(-1, 64*4*4)
        x = self.fc1(x)
        x = self.fc2(x)
        return x

net = Net()
net.cuda()

criterion = torch.nn.CrossEntropyLoss()
optimizer = torch.optim.Adam(net.parameters(), lr=LR)

网络结构如下：

Net(
  (conv1): Sequential(
    (0): Conv2d(3, 16, kernel_size=(3, 3), stride=(1, 1), padding=(1, 1))
    (1): ReLU()
    (2): MaxPool2d(kernel_size=2, stride=2, padding=0, dilation=1, ceil_mode=False)
  )
  (conv2): Sequential(
    (0): Conv2d(16, 32, kernel_size=(3, 3), stride=(1, 1), padding=(1, 1))
    (1): ReLU()
    (2): MaxPool2d(kernel_size=2, stride=2, padding=0, dilation=1, ceil_mode=False)
  )
  (conv3): Sequential(
    (0): Conv2d(32, 64, kernel_size=(3, 3), stride=(1, 1), padding=(1, 1))
    (1): ReLU()
    (2): MaxPool2d(kernel_size=2, stride=2, padding=0, dilation=1, ceil_mode=False)
  )
  (fc1): Sequential(
    (0): Linear(in_features=1024, out_features=32, bias=True)
    (1): ReLU()
  )
  (fc2): Linear(in_features=32, out_features=10, bias=True)
)

网络创建了3个卷积层，1个全连接层

CNN_2

import torch
LR = 0.005

class Net(torch.nn.Module):
    """Some Information about CNN"""

    def __init__(self):
        super(Net, self).__init__()
        self.conv1 = torch.nn.Sequential(
            torch.nn.Conv2d(3, 16, 3, padding=1),  # 3*32*32 -> 16*32*32
            torch.nn.ReLU(),
        )
        self.conv2 = torch.nn.Sequential(
            torch.nn.Conv2d(16, 32, 3, padding=1),  # 16*32*32 -> 32*32*32
            torch.nn.ReLU(),
            torch.nn.MaxPool2d(2, 2)  # 32*32*32-> 32*16*16
        )
        self.conv3 = torch.nn.Sequential(
            torch.nn.Conv2d(32, 64, 3, padding=1),  #  32*16*16 -> 64*16*16
            torch.nn.ReLU(),
        )

        self.conv4 = torch.nn.Sequential(
            torch.nn.Conv2d(64, 128, 3, padding=1),  #  64*16*16 -> 128*16*16
            torch.nn.ReLU(),
            torch.nn.MaxPool2d(2, 2)  # 128*16*16 -> 128*8*8
        )

        self.conv5 = torch.nn.Sequential(
            torch.nn.Conv2d(128, 256, 3, padding=1),  #  128*8*8 -> 256*8*8
            torch.nn.ReLU(),
            torch.nn.MaxPool2d(2, 2)  # 256*8*8 -> 256*4*4
        )

        self.gap = torch.nn.AvgPool2d(4,4)
        self.fc = torch.nn.Linear(256, 10)

    def forward(self, x):
        x = self.conv1(x)
        x = self.conv2(x)
        x = self.conv3(x)
        x = self.conv4(x)
        x = self.conv5(x)
        x = self.gap(x)
        x = x.view(-1, 256)
        x = self.fc(x)
        return x

net = Net()
net.cuda()

criterion = torch.nn.CrossEntropyLoss()
optimizer = torch.optim.Adam(net.parameters(), lr=LR)

打印网络如下：

Net(
  (conv1): Sequential(
    (0): Conv2d(3, 16, kernel_size=(3, 3), stride=(1, 1), padding=(1, 1))
    (1): ReLU()
  )
  (conv2): Sequential(
    (0): Conv2d(16, 32, kernel_size=(3, 3), stride=(1, 1), padding=(1, 1))
    (1): ReLU()
    (2): MaxPool2d(kernel_size=2, stride=2, padding=0, dilation=1, ceil_mode=False)
  )
  (conv3): Sequential(
    (0): Conv2d(32, 64, kernel_size=(3, 3), stride=(1, 1), padding=(1, 1))
    (1): ReLU()
  )
  (conv4): Sequential(
    (0): Conv2d(64, 128, kernel_size=(3, 3), stride=(1, 1), padding=(1, 1))
    (1): ReLU()
    (2): MaxPool2d(kernel_size=2, stride=2, padding=0, dilation=1, ceil_mode=False)
  )
  (conv5): Sequential(
    (0): Conv2d(128, 256, kernel_size=(3, 3), stride=(1, 1), padding=(1, 1))
    (1): ReLU()
    (2): MaxPool2d(kernel_size=2, stride=2, padding=0, dilation=1, ceil_mode=False)
  )
  (gap): AvgPool2d(kernel_size=4, stride=4, padding=0)
  (fc): Linear(in_features=256, out_features=10, bias=True)
)

创建了5个卷积层，最后使用GAP连接输出层

定义训练函数和测试函数

为了方便对不同的网络进行训练和测试，因此，定义一个通用的训练函数和测试函数，方便使用

定义训练函数

def train(model, criterion, optimizer, trainloader, epochs=5, log_interval=50):
    print('----- Train Start -----')
    for epoch in range(epochs):
        running_loss = 0.0
        for step, (batch_x, batch_y) in enumerate(trainloader):
            batch_x, batch_y = batch_x.cuda(), batch_y.cuda()

            output = model(batch_x)

            optimizer.zero_grad()
            loss = criterion(output, batch_y)
            loss.backward()
            optimizer.step()

            running_loss += loss.item()
            if step % log_interval == (log_interval-1):
                print('[%d, %5d] loss: %.4f' %
                      (epoch + 1, step + 1, running_loss / log_interval))
                running_loss = 0.0
    print('----- Train Finished -----')

定义测试函数

def test(model, testloader):
    print('------ Test Start -----')

    correct = 0
    total = 0

    with torch.no_grad():
        for test_x, test_y in testloader:
            images, labels = test_x.cuda(), test_y.cuda()
            output = model(images)
            _, predicted = torch.max(output.data, 1)
            total += labels.size(0)
            correct += (predicted == labels).sum().item()

    accuracy = 100 * correct / total
    print('Accuracy of the network is: %.4f %%' % accuracy)
    return accuracy

在测试集上运行网络

测试CNN_1网络

train(CNN_1.net, CNN_1.criterion, CNN_1.optimizer, trainloader, epochs=EPOCHS)
test(CNN_1.net, testloader)

测试CNN_2网络

train(CNN_2.net, CNN_2.criterion, CNN_2.optimizer, trainloader, epochs=EPOCHS)
test(CNN_2.net, testloader)

训练结果

CNN_1在10代训练后，在测试集准确率上能够达到71.1100 %

CNN_2在10代训练后，在测试集准确率上能够达到75.6700 %

代码

链接：https://pan.baidu.com/s/1rOmiE35rQnszmYyyN6h16Q
提取码：zqf2
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