mnist.py

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

BATCH_SIZE=100 # 批次大小
EPOCHS=200 # 总共训练批次
DEVICE = torch.device("cuda" if torch.cuda.is_available() else "cpu") # 让torch判断是否使用GPU，建议使用GPU环境，因为会快很多

class ConvNet(nn.Module):
    def __init__(self):
        super().__init__()
        # 1,28x28
        self.conv1=nn.Conv2d(1 ,10,5) # 24x24
        self.pool = nn.MaxPool2d(2,2) # 12x12
        self.conv2=nn.Conv2d(10,20,3) # 10x10
        self.fc1 = nn.Linear(20*10*10,500)
        self.fc2 = nn.Linear(500,10)
    def forward(self,x):
        in_size = x.size(0)
        out = self.conv1(x) #24
        out = F.relu(out)
        out = self.pool(out)  #12
        out = self.conv2(out) #10
        out = F.relu(out)
        out = out.view(in_size,-1)
        out = self.fc1(out)
        out = F.relu(out)
        out = self.fc2(out)
        out = F.log_softmax(out,dim=1)
        return out

train_loader = torch.utils.data.DataLoader(
        datasets.MNIST('data', train=True, download=True,
                       transform=transforms.Compose([
                           transforms.ToTensor(),
                           transforms.Normalize((0.1307,), (0.3081,))
                       ])),
        batch_size=BATCH_SIZE, shuffle=True)


test_loader = torch.utils.data.DataLoader(
        datasets.MNIST('data', train=False, transform=transforms.Compose([
                           transforms.ToTensor(),
                           transforms.Normalize((0.1307,), (0.3081,))
                       ])),
        batch_size=BATCH_SIZE, shuffle=True)

model = ConvNet().to(DEVICE)
optimizer = optim.Adam(model.parameters())

def train(model, device, train_loader, optimizer, epoch):
    model.train()
    for batch_idx, (data, target) in enumerate(train_loader):
        data, target = data.to(device), target.to(device)
        optimizer.zero_grad()
        output = model(data)
        print(target.size())
#        print(output)
        loss = F.nll_loss(output, target)
        loss.backward()
        break

#        for name, parms in model.named_parameters():
#            if name == "fc2.weight":
#                print('-->name:', name, '-->grad_requirs:',parms.requires_grad, \
#		        ' -->grad_value:',parms.grad)
#            if name == "fc2.bias":
#                print('-->name:', name, '-->grad_requirs:',parms.requires_grad, \
#                 ' -->grad_value:',parms.grad)
        optimizer.step()
#        if(batch_idx+1)%30 == 0:
#            print('Train Epoch: {} [{}/{} ({:.0f}%)]\tLoss: {:.6f}'.format(
#                epoch, batch_idx * len(data), len(train_loader.dataset),
#                100. * batch_idx / len(train_loader), loss.item()))

def test(model, device, test_loader):
    model.eval()
    test_loss = 0
    correct = 0
    with torch.no_grad():
        for data, target in test_loader:
            data, target = data.to(device), target.to(device)
            output = model(data)
            test_loss += F.nll_loss(output, target, reduction='sum').item() # 将一批的损失相加
            pred = output.max(1, keepdim=True)[1] # 找到概率最大的下标
            correct += pred.eq(target.view_as(pred)).sum().item()

    test_loss /= len(test_loader.dataset)
    print('\nTest set: Average loss: {:.4f}, Accuracy: {}/{} ({:.2f}%)\n'.format(
        test_loss, correct, len(test_loader.dataset),
        100. * correct / len(test_loader.dataset)))


for epoch in range(1, EPOCHS + 1):
    train(model, DEVICE, train_loader, optimizer, epoch)
#    test(model, DEVICE, test_loader)
    break