machine-learning - 变分自动编码器的采样问题

Question

我的 vae 课程如下所示：

class Encoder(nn.Module):
def __init__(self):
    super(Encoder, self).__init__()
    c = capacity
    self.conv1 = nn.Conv2d(in_channels=1, out_channels=c, kernel_size=4, stride=2, padding=1) # out: c x 14 x 14
    self.conv2 = nn.Conv2d(in_channels=c, out_channels=c*2, kernel_size=4, stride=2, padding=1) # out: c x 7 x 7
    self.fc_mu = nn.Linear(in_features=c*2*7*7, out_features=latent_dims)
    self.fc_logvar = nn.Linear(in_features=c*2*7*7, out_features=latent_dims)
        
def forward(self, x):
    x = F.relu(self.conv1(x))
    x = F.relu(self.conv2(x))
    x = x.view(x.size(0), -1) # flatten batch of multi-channel feature maps to a batch of feature vectors
    x_mu = self.fc_mu(x)
    x_logvar = self.fc_logvar(x)
    return x_mu, x_logvar

class Decoder(nn.Module):
def __init__(self):
    super(Decoder, self).__init__()
    c = capacity
    self.fc = nn.Linear(in_features=latent_dims, out_features=c*2*7*7)
    self.conv2 = nn.ConvTranspose2d(in_channels=c*2, out_channels=c, kernel_size=4, stride=2, padding=1)
    self.conv1 = nn.ConvTranspose2d(in_channels=c, out_channels=1, kernel_size=4, stride=2, padding=1)
        
def forward(self, x):
    x = self.fc(x)
    x = x.view(x.size(0), capacity*2, 7, 7) # unflatten batch of feature vectors to a batch of multi-channel feature maps
    x = F.relu(self.conv2(x))
    x = torch.sigmoid(self.conv1(x)) # last layer before output is sigmoid, since we are using BCE as reconstruction loss
    return x

class VariationalAutoencoder(nn.Module):
def __init__(self):
    super(VariationalAutoencoder, self).__init__()
    self.encoder = Encoder()
    self.decoder = Decoder()

def forward(self, x):
    latent_mu, latent_logvar = self.encoder(x)
    latent = self.latent_sample(latent_mu, latent_logvar)
    x_recon = self.decoder(latent)
    return x_recon, latent_mu, latent_logvar

def latent_sample(self, mu, logvar):
    if self.training:
        # the reparameterization trick
        std = logvar.mul(0.5).exp_()
        eps = torch.empty_like(std).normal_()
        return eps.mul(std).add_(mu)
    else:
        return mu

def vae_loss(recon_x, x, mu, logvar):
# recon_x is the probability of a multivariate Bernoulli distribution p.
# -log(p(x)) is then the pixel-wise binary cross-entropy.
# Averaging or not averaging the binary cross-entropy over all pixels here
# is a subtle detail with big effect on training, since it changes the weight
# we need to pick for the other loss term by several orders of magnitude.
# Not averaging is the direct implementation of the negative log likelihood,
# but averaging makes the weight of the other loss term independent of the image resolution.
recon_loss = F.binary_cross_entropy(recon_x.view(-1, 784), x.view(-1, 784), reduction='sum')

kldivergence = -0.5 * torch.sum(1 + logvar - mu.pow(2) - logvar.exp())

return recon_loss + variational_beta * kldivergence

我在 MNIST 数据集上训练它。我想对其进行采样，或生成一个数组并将其提供给解码器并查看输出将是什么。

问题是我不太明白，我的 z 数组应该是什么样子以及它应该需要什么形状。

这是采样的代码：

z = ...
input = torch.FloatTensor(z).to(device)  
vae.eval()
output = vae.decoder(input)
plot_gallery(output.data.cpu().numpy(), 24, 24, n_row=5, n_col=5)

标签： machine-learningpytorchautoencoder