main.py

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

# Define the encoder part of the VAE
class Encoder(nn.Module):
    def __init__(self, input_dim, hidden_dim, z_dim):
        super(Encoder, self).__init__()
        self.fc1 = nn.Linear(input_dim, hidden_dim)
        self.fc2_mu = nn.Linear(hidden_dim, z_dim)
        self.fc2_logvar = nn.Linear(hidden_dim, z_dim)

    def forward(self, x):
        h = torch.relu(self.fc1(x))
        mu = self.fc2_mu(h)
        logvar = self.fc2_logvar(h)
        return mu, logvar

# Define the decoder part of the VAE
class Decoder(nn.Module):
    def __init__(self, z_dim, hidden_dim, output_dim):
        super(Decoder, self).__init__()
        self.fc1 = nn.Linear(z_dim, hidden_dim)
        self.fc2 = nn.Linear(hidden_dim, output_dim)

    def forward(self, z):
        h = torch.relu(self.fc1(z))
        x_recon = torch.sigmoid(self.fc2(h))
        return x_recon

# Define the VAE model
class VAE(nn.Module):
    def __init__(self, input_dim, hidden_dim, z_dim):
        super(VAE, self).__init__()
        self.encoder = Encoder(input_dim, hidden_dim, z_dim)
        self.decoder = Decoder(z_dim, hidden_dim, input_dim)

    def reparameterize(self, mu, logvar):
        std = torch.exp(0.5 * logvar)
        eps = torch.randn_like(std)
        return mu + eps * std

    def forward(self, x):
        mu, logvar = self.encoder(x)
        z = self.reparameterize(mu, logvar)
        x_recon = self.decoder(z)
        return x_recon, mu, logvar

# Loss function
def loss_function(x_recon, x, mu, logvar):
    BCE = nn.functional.binary_cross_entropy(x_recon, x, reduction='sum')
    KLD = -0.5 * torch.sum(1 + logvar - mu.pow(2) - logvar.exp())
    return BCE + KLD

# Hyperparameters
input_dim = 28 * 28
hidden_dim = 400
z_dim = 20
batch_size = 128
learning_rate = 1e-3
num_epochs = 10

# Data loading
transform = transforms.ToTensor()
train_dataset = datasets.MNIST(root='./data', train=True, transform=transform, download=True)
train_loader = DataLoader(dataset=train_dataset, batch_size=batch_size, shuffle=True)

# Model, optimizer
model = VAE(input_dim, hidden_dim, z_dim)
optimizer = optim.Adam(model.parameters(), lr=learning_rate)

# Training loop
model.train()
for epoch in range(num_epochs):
    train_loss = 0
    for batch_idx, (data, _) in enumerate(train_loader):
        data = data.view(-1, 28 * 28)  # Flatten the input data
        optimizer.zero_grad()
        x_recon, mu, logvar = model(data)
        loss = loss_function(x_recon, data, mu, logvar)
        loss.backward()
        train_loss += loss.item()
        optimizer.step()

    print(f'Epoch {epoch + 1}, Loss: {train_loss / len(train_loader.dataset)}')

# Save the trained model
torch.save(model.state_dict(), 'vae.pth')