神经网络VGGNet训练CIFAR10数据集

VGG网络结构

       

基本的单元（vgg_block）是几个卷积再加上一个池化，这个单元结构反复出现，用一个函数封装(vgg_stack).

import numpy as np
import torch
from torch import nn
from torch.autograd import Variable
from torchvision.datasets import CIFAR10
from torchvision import transforms
import torch.nn.functional as F
from utils import train


def vgg_block(num_convs, in_channels, out_channels):
    net = [nn.Conv2d(in_channels, out_channels, kernel_size=3, padding=1),
           nn.ReLU(True)]  # 定义第一层卷积层

    for i in range(num_convs-1):  # 定义后面的num_convs-1层卷积层
        net.append(nn.Conv2d(out_channels, out_channels, kernel_size=3, padding=1))
        net.append(nn.ReLU(True))

    net.append(nn.MaxPool2d(2, 2))  # 定义池化层
    return nn.Sequential(*net)


# 每个vgg_block的卷积层层数是num_convs,输入、输出通道数保存在channels中
def vgg_stack(num_convs, channels):
    net = []
    for n, c in zip(num_convs, channels):
        in_c = c[0]
        out_c = c[1]
        net.append(vgg_block(n, in_c, out_c))
    return nn.Sequential(*net)
# 定义一个vgg结构，其中有五个卷积层，每个vgg_block的卷积层分别是1,1,2,2,2
# 每个模块的输入、输出通道数如下
vgg_net = vgg_stack((1, 1, 2, 2, 2), ((3, 64), (64, 128), (128, 256), (256, 512), (512, 512)))
# print(vgg_net)


class vgg(nn.Module):
    def __init__(self):
        super(vgg, self).__init__()
        self.feature = vgg_net
        self.fc = nn.Sequential(
            nn.Linear(512, 100),
            nn.ReLU(True),
            nn.Linear(100, 10)
        )

    def forward(self, x):
        x = self.feature(x)
        x = x.view(x.shape[0], -1)
        x = self.fc(x)
        return x


def data_tf(x):
    x = np.array(x, dtype='float32') / 255
    x = (x-0.5)/0.5  # 标准化
    x = x.transpose((2, 0, 1))  # 将channel放到第一维，只是pytorch要求的输入方式
    x = torch.from_numpy(x)
    return x


train_set = CIFAR10('./data', train=True, transform=data_tf, download=False)
train_data = torch.utils.data.DataLoader(train_set, batch_size=128, shuffle=True)
test_set = CIFAR10('./data', train=False, transform=data_tf, download=False)
test_data = torch.utils.data.DataLoader(test_set, batch_size=128, shuffle=False)

net = vgg().cuda()
optimizer = torch.optim.SGD(net.parameters(), lr=1e-2)
criterion = nn.CrossEntropyLoss()


train(net, train_data, test_data, 20, optimizer, criterion)

utils.py

from datetime import datetime

import torch
import torch.nn.functional as F
from torch import nn
from torch.autograd import Variable


def get_acc(output, label):
    total = output.shape[0]
    _, pred_label = output.max(1)
    num_correct = (pred_label == label).sum().data[0]
    return num_correct / total


def train(net, train_data, valid_data, num_epochs, optimizer, criterion):
    if torch.cuda.is_available():
        net = net.cuda()
    prev_time = datetime.now()
    for epoch in range(num_epochs):
        train_loss = 0
        train_acc = 0
        net = net.train()
        for im, label in train_data:
            if torch.cuda.is_available():
                im = Variable(im.cuda())  # (bs, 3, h, w)
                label = Variable(label.cuda())  # (bs, h, w)
            else:
                im = Variable(im)
                label = Variable(label)
            # forward
            output = net(im)
            loss = criterion(output, label)
            # backward
            optimizer.zero_grad()
            loss.backward()
            optimizer.step()

            train_loss += loss.data[0]
            train_acc += get_acc(output, label)

        cur_time = datetime.now()
        h, remainder = divmod((cur_time - prev_time).seconds, 3600)
        m, s = divmod(remainder, 60)
        time_str = "Time %02d:%02d:%02d" % (h, m, s)
        if valid_data is not None:
            valid_loss = 0
            valid_acc = 0
            net = net.eval()
            for im, label in valid_data:
                if torch.cuda.is_available():
                    im = Variable(im.cuda(), volatile=True)
                    label = Variable(label.cuda(), volatile=True)
                else:
                    im = Variable(im, volatile=True)
                    label = Variable(label, volatile=True)
                output = net(im)
                loss = criterion(output, label)
                valid_loss += loss.data[0]
                valid_acc += get_acc(output, label)
            epoch_str = (
                "Epoch %d. Train Loss: %f, Train Acc: %f, Valid Loss: %f, Valid Acc: %f, "
                % (epoch, train_loss / len(train_data),
                   train_acc / len(train_data), valid_loss / len(valid_data),
                   valid_acc / len(valid_data)))
        else:
            epoch_str = ("Epoch %d. Train Loss: %f, Train Acc: %f, " %
                         (epoch, train_loss / len(train_data),
                          train_acc / len(train_data)))
        prev_time = cur_time
        print(epoch_str + time_str)

 上述代码用的batch_size是128，训练一次数据集大概需要三分钟多，如果改成64，大概需要五分钟多。

训练结果：

训练到第八次的时候，训练集的准确率就达到了99.1%,测试集达到了98.9%