import torch import torch.nn as nn import torch.optim as optim import torchvision # datasets and pretrained neural nets import torch.utils.data import torch.nn.functional as F import torchvision.transforms as transforms transform = transforms.Compose([transforms.ToTensor(), ]) trainset = torchvision.datasets.MNIST(root='.\mydata', train=True, download=True, transform=transform) #文件夹地址可自定义 testset = torchvision.datasets.MNIST(root='.\mydata', train=False, download=True, transform=transform) #文件夹地址可自定义 trainloader = torch.utils.data.DataLoader(trainset, batch_size =32, shuffle=True) testloader = torch.utils.data.DataLoader(testset, batch_size=32, shuffle=False)写一个构建网络定义损失函数，优化器训练 迭代次数为10次 模型评测尝试将数据集更改为FashionMNIST或者CIFIR10再训练模型，或对比卷积神经网络和全连接神经网络模型的预测准确度，或尝试数据增强方法的代码

好的，这里是一个简单的代码示例，包括构建网络、定义损失函数、优化器、训练和评估模型的步骤。同时，也包括了针对FashionMNIST数据集和CIFAR10数据集的代码，以及卷积神经网络和全连接神经网络模型的比较，以及数据增强方法的代码。

import torch
import torch.nn as nn
import torch.optim as optim
import torchvision
import torch.utils.data
import torch.nn.functional as F
import torchvision.transforms as transforms

# 数据集选项
dataset = 'MNIST'  # 可以选择'MNIST', 'FashionMNIST'或者'CIFAR10'
data_root = './data'  # 数据集存储的文件夹地址

# 构建网络
class Net(nn.Module):
    def __init__(self):
        super(Net, self).__init__()
        self.fc1 = nn.Linear(28 * 28, 128)
        self.fc2 = nn.Linear(128, 10)

    def forward(self, x):
        x = x.view(-1, 28 * 28)
        x = F.relu(self.fc1(x))
        x = self.fc2(x)
        return x

# 定义损失函数和优化器
net = Net()
criterion = nn.CrossEntropyLoss()
optimizer = optim.SGD(net.parameters(), lr=0.001, momentum=0.9)

# 加载数据集
if dataset == 'MNIST':
    trainset = torchvision.datasets.MNIST(root=data_root, train=True, download=True, transform=transforms.ToTensor())
    testset = torchvision.datasets.MNIST(root=data_root, train=False, download=True, transform=transforms.ToTensor())
elif dataset == 'FashionMNIST':
    trainset = torchvision.datasets.FashionMNIST(root=data_root, train=True, download=True, transform=transforms.ToTensor())
    testset = torchvision.datasets.FashionMNIST(root=data_root, train=False, download=True, transform=transforms.ToTensor())
elif dataset == 'CIFAR10':
    trainset = torchvision.datasets.CIFAR10(root=data_root, train=True, download=True, transform=transforms.ToTensor())
    testset = torchvision.datasets.CIFAR10(root=data_root, train=False, download=True, transform=transforms.ToTensor())
else:
    raise ValueError('Invalid dataset name')

trainloader = torch.utils.data.DataLoader(trainset, batch_size=32, shuffle=True)
testloader = torch.utils.data.DataLoader(testset, batch_size=32, shuffle=False)

# 训练模型
for epoch in range(10):
    running_loss = 0.0
    for i, data in enumerate(trainloader, 0):
        inputs, labels = data
        optimizer.zero_grad()
        outputs = net(inputs)
        loss = criterion(outputs, labels)
        loss.backward()
        optimizer.step()
        running_loss += loss.item()
        if i % 100 == 99:
            print('[%d, %5d] loss: %.3f' % (epoch + 1, i + 1, running_loss / 100))
            running_loss = 0.0

print('Finished Training')

# 评估模型
correct = 0
total = 0
with torch.no_grad():
    for data in testloader:
        images, labels = data
        outputs = net(images)
        _, predicted = torch.max(outputs.data, 1)
        total += labels.size(0)
        correct += (predicted == labels).sum().item()

print('Accuracy of the network on the 10000 test images: %d %%' % (100 * correct / total))

针对FashionMNIST数据集和CIFAR10数据集的代码仅需要改变数据集的名称和地址即可。卷积神经网络和全连接神经网络模型的比较可以使用以下代码：

# 定义卷积神经网络
class ConvNet(nn.Module):
    def __init__(self):
        super(ConvNet, self).__init__()
        self.conv1 = nn.Conv2d(1, 16, kernel_size=5, padding=2)
        self.conv2 = nn.Conv2d(16, 32, kernel_size=5, padding=2)
        self.fc1 = nn.Linear(32 * 7 * 7, 256)
        self.fc2 = nn.Linear(256, 10)

    def forward(self, x):
        x = F.relu(self.conv1(x))
        x = F.max_pool2d(x, 2)
        x = F.relu(self.conv2(x))
        x = F.max_pool2d(x, 2)
        x = x.view(-1, 32 * 7 * 7)
        x = F.relu(self.fc1(x))
        x = self.fc2(x)
        return x

# 定义全连接神经网络
class FCNet(nn.Module):
    def __init__(self):
        super(FCNet, self).__init__()
        self.fc1 = nn.Linear(28 * 28, 128)
        self.fc2 = nn.Linear(128, 10)

    def forward(self, x):
        x = x.view(-1, 28 * 28)
        x = F.relu(self.fc1(x))
        x = self.fc2(x)
        return x

if dataset == 'MNIST' or dataset == 'FashionMNIST':
    net = FCNet()
elif dataset == 'CIFAR10':
    net = ConvNet()
else:
    raise ValueError('Invalid dataset name')

# 训练和评估模型的代码和之前相同

最后，以下是数据增强的代码示例，可以在训练数据集上应用随机的图像变换，从而增加数据集的多样性和泛化性能。

# 数据增强
train_transform = transforms.Compose([
    transforms.RandomCrop(28, padding=4),
    transforms.RandomHorizontalFlip(),
    transforms.ToTensor(),
])

trainset = torchvision.datasets.MNIST(root=data_root, train=True, download=True, transform=train_transform)
trainloader = torch.utils.data.DataLoader(trainset, batch_size=32, shuffle=True)

# 训练模型的代码和之前相同

需要注意的是，在评估模型时，不应该使用数据增强，因为这会导致测试结果不准确。