零基础学习人工智能—Python—Pytorch学习(九)

前言

本文主要介绍卷积神经网络的使用的下半部分。

另外,上篇文章增加了一点代码注释,主要是解释(w-f+2p)/s+1这个公式的使用。

所以,要是这篇文章的代码看不太懂,可以翻一下上篇文章。

代码实现

之前,我们已经学习了概念,在结合我们以前学习的知识,我们可以直接阅读下面代码了。

代码里使用了,dataset.CIFAR10数据集。

CIFAR-10 数据集由 60000 张 32x32 彩色图像组成,共分为 10 个不同的类别,分别是飞机、汽车、鸟、猫、鹿、狗、青蛙、马、船和卡车。

每个类别包含 6000 张图像,其中 50000 张用于训练,10000 张用于测试。

import torch
import torch.nn as nn
import torchvision
import torchvision.transforms as transforms
import matplotlib.pyplot as plt
import numpy as np
import torch.nn.functional as F #nn不好使时,在这里找激活函数
# device config
device = torch.device('cuda' if torch.cuda.is_available() else 'cpu')
# hyper parameters
input_size = 784  # 28x28
hidden_size = 100
num_classes = 10
batch_size = 100
learning_rate = 0.001
num_epochs = 2

 
transform = transforms.Compose(
    [transforms.ToTensor(), transforms.Normalize((0.5, 0.5, 0.5), (0.5, 0.5, 0.5))])

train_dataset = torchvision.datasets.CIFAR10(
    root='./data', train=True, download=True, transform=transform)

test_dataset = torchvision.datasets.CIFAR10(
    root='./data', train=False, download=True, transform=transform)
 
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=False)
print('每份100个,被分成多少份:', len(test_loader))


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


class ConvNet(nn.Module):
    def __init__(self):
        super(ConvNet,self).__init__()
        self.conv1 = nn.Conv2d(3, 6, 5)
        self.pool = nn.MaxPool2d(2, 2)
        self.conv2 = nn.Conv2d(6, 16, 5)
        self.fc1 = nn.Linear(16*5*5, 120) #这个在forward里解释
        self.fc2 = nn.Linear(120, 84)
        self.fc3 = nn.Linear(84, 10)

    def forward(self, x):
        x = self.pool(F.relu(self.conv1(x)))
        x = self.pool(F.relu(self.conv2(x))) #这里x已经变成 torch.Size([4, 16, 5, 5])
        # print("两次卷积两次池化后的x.shape:",x.shape)
        x = x.view(-1,16*5*5)#这里的16*5*5就是x的后面3个维度相乘
        x = F.relu(self.fc1(x)) #fc1定义时,inputx已经是6*5*5了
        x = F.relu(self.fc2(x))
        x= self.fc3(x)
        return x


model = ConvNet().to(device)
criterion = nn.CrossEntropyLoss()
optimizer = torch.optim.SGD(model.parameters(), lr=learning_rate)


n_total_steps = len(train_loader)

for epoch in range(num_epochs):
    for i, (images, labels) in enumerate(train_loader):
        # origin shape:[4,3,32,32]=4,3,1024
        # input layer: 3 input channels, 6 output channels, 5 kernel size
        images = images.to(device)
        labels = labels.to(device)
        # Forward pass
        outputs = model(images)
        loss = criterion(outputs, labels)

        # Backward and optimize
        optimizer.zero_grad()
        loss.backward()
        optimizer.step()
        if (i+1) % 2000 == 0:
            print(
                f'Epoch [{epoch+1}/{num_epochs}], Step [{i+1}/{n_total_steps}], Loss: {loss.item():.4f}')
print('Finished Training')


# test
with torch.no_grad():
    n_correct = 0
    n_samples = 0
    n_class_correct = [0 for i in range(10)] #生成 10 个 0 的列表
    n_class_samples = [0 for i in range(10)]
    for images, labels in test_loader:
        images = images.to(device)
        labels = labels.to(device)
        print('test-images.shape:', images.shape)
        outputs = model(images)
        # max returns(value ,index)
        _, predicted = torch.max(outputs, 1)
        n_samples += labels.size(0)
        n_correct += (predicted == labels).sum().item()
        for i in range(batch_size):
            label = labels[i]
            # print("label:",label) #这里存的是 0~9的数字 输出就是这样的 label: tensor(2) predicted[i]也是这样的数
            pred = predicted[i]
            if (label == pred):
                n_class_correct[label] += 1
            n_class_samples[label] += 1
    acc = 100.0*n_correct/n_samples  # 计算正确率
    print(f'accuracy ={acc}')
    
    for i in range(10):
        acc = 100.0*n_class_correct[i]/n_class_samples[i]
        print(f'Accuracy of {classes[i]}: {acc} %')

运行结果如下:

accuracy =10.26
Accuracy of plane: 0.0 %
Accuracy of car: 0.0 %
Accuracy of bird: 0.0 %
Accuracy of cat: 0.0 %
Accuracy of deer: 0.0 %
Accuracy of dog: 0.0 %
Accuracy of frog: 0.0 %
Accuracy of horse: 0.0 %
Accuracy of ship: 89.6 %
Accuracy of truck: 13.0 %

这是因为我设置的num_epochs=2,也就是循环的次数太低,所以结果的精确度就很低。

我们只要增加epochs的值,就能提高精确度了。


传送门:
零基础学习人工智能---Python---Pytorch学习---全集

这样我们卷积神经网络就学完了。


注:此文章为原创,任何形式的转载都请联系作者获得授权并注明出处!



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https://www.cnblogs.com/kiba/p/18381036