• 🍨 本文为🔗365天深度学习训练营 中的学习记录博客
• 🍦 参考文章：365天深度学习训练营-第P2周：彩色识别
• 🍖 原作者：K同学啊 | 接辅导、项目定制
• 🚀 文章来源：K同学的学习圈子

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上周使用Pytorch构建卷积神经网络，实现了MNIST手写数字的识别，这周的目标是CIFAR10中复杂的彩色图像分类。

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环境

• 系统：Linux
• 语言： Python 3.8.10
• 深度学习框架：PyTorch 2.0.0+cu118

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步骤

环境设置

包引用

import torch
import torch.nn as nn
import torch.optim as optim
import torch.nn.functional as F
from torch.utils.data import DataLoader
from torchvision import datasets, transforms

import numpy as np
import matplotlib.pyplot as plt
from torchinfo import summary # 方便像tensorflow一样打印模型

硬件设备

device = torch.device('cuda' if torch.cuda.is_available() else 'cpu')

数据准备

数据集下载与加载

train_dataset = datasets.CIFAR10(root='data', train=True, 
					download=True, transform=transforms.ToTensor()) # 不要忘记这个transform
test_dataset = datasets.CIFAR10(root='data', train=False, 
					download=True, transform=transforms.ToTensor())

数据集预览

image, label = train_dataset[0]
print(image.shape)
plt.figure(figsize=(20,4))
for i in range(20):
	image, label = train_dataset[i]
	plt.subplot(2, 10, i+1)
	plt.imshow(image.numpy().transpose(1,2,0)
	plt.axis('off')
	plt.title(label) # 加载的数据集没有对应的名称，暂时展示它们的id

数据集准备

batch_size = 32
train_loader = DataLoader(train_dataset, shuffle=True, batch_size=batch_size)
test_loader = DataLoader(test_dataset, batch_size=batch_size)

模型设计

class Model(nn.Module):
	def __init__(self, num_classes):
		super().__init__()
		# 3x3的卷积无padding每次宽高-2
		# 2x2的最大池化，每次宽高缩短为原来的一半
		# 32x32 -> conv1 -> 30x30 -> maxpool -> 15x15
		self.conv1 = nn.Conv2d(3, 64, kernel_size=3)
		# 15x15 -> conv2 -> 13x13 -> maxpool -> 6x6
		self.conv2 = nn.Conv2d(64, 64, kernel_size=3)
		# 6x6 -> conv3 -> 4x4 -> maxpool -> 2x2
		self.conv3 = nn.Conv2d(64, 128, kernel_size=3)
		self.maxpool = nn.MaxPool2d(2),
		self.flatten = nn.Flatten(),
		self.fc1 = nn.Linear(2*2*128, 256)
		self.fc2 = nn.Linear(256, num_classes)

	def forward(self, x):
		x = F.relu(self.conv1(x))
		x = self.maxpool(x)

		x = F.relu(self.conv2(x))
		x = self.maxpool(x)

		x = F.relu(self.conv3(x))
		x = self.maxpool(x)

		x = self.flatten(x)

		x = F.relu(self.fc1(x))
		x = self.fc2(x)
		return x

model = Model(10).to(device)
summary(model, input_size=(1, 3, 32, 32))

模型训练

超参数设置

learning_rate = 1e-2
epochs = 10
loss_fn = nn.CrossEntropyLoss()
optimizer = optim.SGD(model.parameters(), lr=learning_rate)

helper函数

def train(train_loader, model, loss_fn, optimizer):
	size = len(train_loader.dataset)
	num_batches = len(train_loader)

	train_loss, train_acc = 0, 0
	for x, y in train_loader:
		x, y = x.to(device), y.to(device)

		preds = model(x)
		loss = loss_fn(preds, y)

		optimizer.zero_grad()
		loss.backward()
		optimizer.step()

		train_loss += loss.item()
		train_acc += (preds.argmax(1) == y).type(torch.float).sum().item()

	train_loss /= num_batches
	train_acc /= size

	return train_loss, train_acc

def test(test_loader, model, loss_fn):
	size = len(test_loader.dataset)
	num_batches = len(test_loader)

	test_loss, test_acc = 0, 0
	with torch.no_grad():
		for x, y in test_loader:
			x, y = x.to(device), y.to(device)
			
			preds = model(x)
			loss = loss_fn(preds, y)
			
			test_loss += loss.item()
			test_acc += (preds.argmax(1) == y).type(torch.float).sum().item()

	test_loss /= num_batches
	test_acc /= size

	return test_loss, test_acc

def fit(train_loader, test_loader, model, loss_fn, optimizer, epochs):
	train_loss, train_acc = [], []
	test_loss, test_acc = [], []
	for epoch in range(epochs):
		model.train()
		epoch_train_loss, epoch_train_acc = train(train_loader, model, loss_fn, optimizer)
		model.eval()
		epoch_test_loss, epoch_test_acc = test(test_loader, model, loss_fn)

		train_loss.append(epoch_train_loss)
		train_acc.append(epoch_train_acc)
		test_loss.append(epoch_test_loss)
		test_acc.append(epoch_test_acc)
	return train_loss, train_acc, test_loss, test_acc

正式训练

train_loss, train_acc, test_loss, test_acc = 
				fit(train_loader, test_loader, model, loss_fn, optimizer, 20)

结果呈现

series = range(len(train_loss))
plt.figure(figsize=(12,4))
plt.subplot(1,2,1)
plt.plot(series, train_loss, label='train loss')
plt.plot(series, test_loss, label='validation loss')
plt.legend(loc='upper right')
plt.title('Loss')
plt.subplot(1,2,2)
plt.plot(series, train_acc, label='train accuracy')
plt.plot(series, test_acc, label='validation accuracy')
plt.legend(loc='lower right')
plt.title('Accuracy')

从结果图可以发现，模型应该还没收敛，将epoch设置为30，重新跑一遍模型。

可以看出20个epoch后，训练集上的正确率持续增长，在验证集上的正确率几乎就不再增长了，符合过拟合的特征。需要对模型进行改进才能提升正确率了。

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总结与心得体会

通过本周的学习，掌握了使用pytorch编写一个完整深度学习的过程，包括环境的配置、数据的准备、模型定义与训练、结果分析呈现等步骤，并且掌握了通过pytorch的API组建一个简单的卷积神经网络的过程。