基于pytorch的采用胶囊网络分类mnist数据集代码

下面是一个基于PyTorch的胶囊网络分类MNIST数据集的代码示例：

import torch
import torch.nn as nn
import torch.optim as optim
import torchvision.datasets as datasets
import torchvision.transforms as transforms

# 定义胶囊层
class CapsuleLayer(nn.Module):
    def __init__(self, num_capsules, num_route_nodes, in_channels, out_channels):
        super(CapsuleLayer, self).__init__()
        self.num_route_nodes = num_route_nodes
        self.num_capsules = num_capsules
        self.route_weights = nn.Parameter(torch.randn(num_capsules, num_route_nodes, in_channels, out_channels))

    def forward(self, x):
        # x shape: batch_size, num_route_nodes, in_channels
        # expand input tensor to match route_weights
        u_hat = torch.matmul(x[:, None, :, None], self.route_weights[None, :, :, :])
        # shape: batch_size, num_capsules, num_route_nodes, out_channels
        b_ij = torch.zeros(x.size(0), self.num_capsules, self.num_route_nodes, 1)
        # 路由算法
        num_iterations = 3
        for i in range(num_iterations):
            c_ij = nn.functional.softmax(b_ij, dim=1)
            s_j = (c_ij * u_hat).sum(dim=2, keepdim=True)
            v_j = self.squash(s_j)
            if i != num_iterations - 1:
                update = (u_hat * v_j).sum(dim=-1, keepdim=True)
                b_ij = b_ij + update
        return v_j.squeeze()

    def squash(self, tensor):
        norm_squared = (tensor ** 2).sum(dim=-1, keepdim=True)
        norm = torch.sqrt(norm_squared)
        scale = norm_squared / (1 + norm_squared)
        return scale * tensor / norm


# 定义胶囊网络
class CapsuleNet(nn.Module):
    def __init__(self):
        super(CapsuleNet, self).__init__()
        self.conv1 = nn.Conv2d(1, 256, kernel_size=9)
        self.primary_caps = CapsuleLayer(num_capsules=8, num_route_nodes=-1, in_channels=256, out_channels=32)
        self.digit_caps = CapsuleLayer(num_capsules=10, num_route_nodes=32, in_channels=8, out_channels=16)
        self.decoder = nn.Sequential(
            nn.Linear(16 * 10, 512),
            nn.ReLU(inplace=True),
            nn.Linear(512, 1024),
            nn.ReLU(inplace=True),
            nn.Linear(1024, 784),
            nn.Sigmoid()
        )

    def forward(self, x):
        x = nn.functional.relu(self.conv1(x))
        x = self.primary_caps(x)
        x = self.digit_caps(x).squeeze().transpose(0, 1)
        classes = (x ** 2).sum(dim=-1) ** 0.5
        classes = nn.functional.softmax(classes, dim=-1)
        _, max_length_indices = classes.max(dim=1)
        masked = torch.autograd.Variable(torch.sparse.torch.eye(10)).cuda()[:, max_length_indices]
        reconstructions = self.decoder((x * masked[:, :, None]).view(x.size(0), -1))
        return classes, reconstructions


# 定义训练函数
def train(model, train_loader, optimizer, criterion, epoch):
    model.train()
    train_loss = 0
    correct = 0
    for batch_idx, (data, target) in enumerate(train_loader):
        data, target = data.cuda(), target.cuda()
        optimizer.zero_grad()
        classes, reconstructions = model(data)
        loss = criterion(data.view(data.size(0), -1), reconstructions) + 0.0005 * (classes ** 2).sum()
        loss.backward()
        optimizer.step()
        train_loss += loss.item()
        pred = classes.data.max(1)[1]
        correct += pred.eq(target.data).cpu().sum()
    print('Train Epoch: {} [{}/{} ({:.0f}%)]\tLoss: {:.6f}\tAccuracy: {:.2f}%'.format(
        epoch, batch_idx * len(data), len(train_loader.dataset),
        100. * batch_idx / len(train_loader), train_loss / len(train_loader),
        100. * correct / len(train_loader.dataset)))


# 定义测试函数
def test(model, test_loader, criterion):
    model.eval()
    test_loss = 0
    correct = 0
    with torch.no_grad():
        for data, target in test_loader:
            data, target = data.cuda(), target.cuda()
            classes, reconstructions = model(data)
            test_loss += criterion(data.view(data.size(0), -1), reconstructions).item()
            pred = classes.data.max(1)[1]
            correct += pred.eq(target.data).cpu().sum()

    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)))


# 加载MNIST数据集
train_dataset = datasets.MNIST(root='./data', train=True, transform=transforms.ToTensor(), download=True)
test_dataset = datasets.MNIST(root='./data', train=False, transform=transforms.ToTensor(), download=True)
train_loader = torch.utils.data.DataLoader(train_dataset, batch_size=128, shuffle=True, num_workers=2)
test_loader = torch.utils.data.DataLoader(test_dataset, batch_size=128, shuffle=False, num_workers=2)

# 实例化模型和优化器
model = CapsuleNet().cuda()
optimizer = optim.Adam(model.parameters())

# 定义损失函数
criterion = nn.MSELoss(reduction='sum')

# 训练模型
for epoch in range(1, 11):
    train(model, train_loader, optimizer, criterion, epoch)
    test(model, test_loader, criterion)

在这个示例中，我们使用PyTorch实现了一个简单的胶囊网络，并使用MNIST数据集对其进行了训练和测试。在训练过程中，我们使用MSE Loss作为损失函数，同时加入Margin Loss以帮助训练网络。在测试过程中，我们使用分类准确率作为性能指标。