python如何利用Adversarial Loss训练神经网络
时间: 2023-12-19 19:06:42 浏览: 27
Adversarial Loss 是一种用于训练生成对抗网络(GAN)的损失函数。GAN 是一种由两个神经网络组成的模型,一个负责生成图像,另一个负责判别生成的图像是否与真实图像相似。GAN 的目标是让生成器生成的图像与真实图像无法被判别器区分,从而达到生成逼真图像的目的。
下面是一个简单的代码示例,演示了如何使用 Adversarial Loss 训练 GAN:
```python
import torch
import torch.nn as nn
import torch.optim as optim
from torchvision import datasets, transforms
from torch.autograd import Variable
# 定义生成器网络
class Generator(nn.Module):
def __init__(self):
super(Generator, self).__init__()
self.fc1 = nn.Linear(100, 128)
self.fc2 = nn.Linear(128, 784)
self.relu = nn.ReLU()
self.sigmoid = nn.Sigmoid()
def forward(self, x):
x = self.fc1(x)
x = self.relu(x)
x = self.fc2(x)
x = self.sigmoid(x)
return x
# 定义判别器网络
class Discriminator(nn.Module):
def __init__(self):
super(Discriminator, self).__init__()
self.fc1 = nn.Linear(784, 128)
self.fc2 = nn.Linear(128, 1)
self.relu = nn.ReLU()
self.sigmoid = nn.Sigmoid()
def forward(self, x):
x = self.fc1(x)
x = self.relu(x)
x = self.fc2(x)
x = self.sigmoid(x)
return x
# 定义损失函数和优化器
adversarial_loss = nn.BCELoss()
generator = Generator()
discriminator = Discriminator()
optimizer_G = optim.Adam(generator.parameters(), lr=0.0002)
optimizer_D = optim.Adam(discriminator.parameters(), lr=0.0002)
# 加载数据集
transform = transforms.Compose([
transforms.ToTensor(),
transforms.Normalize((0.5,), (0.5,))
])
train_dataset = datasets.MNIST(root='./data', train=True, transform=transform, download=True)
train_loader = torch.utils.data.DataLoader(train_dataset, batch_size=64, shuffle=True)
# 训练 GAN
for epoch in range(200):
for i, (images, _) in enumerate(train_loader):
# 训练判别器
discriminator.zero_grad()
real_images = Variable(images.view(-1, 28*28))
real_labels = Variable(torch.ones(images.size(0), 1))
fake_images = Variable(generator(Variable(torch.randn(images.size(0), 100))))
fake_labels = Variable(torch.zeros(images.size(0), 1))
d_loss_real = adversarial_loss(discriminator(real_images), real_labels)
d_loss_fake = adversarial_loss(discriminator(fake_images), fake_labels)
d_loss = d_loss_real + d_loss_fake
d_loss.backward()
optimizer_D.step()
# 训练生成器
generator.zero_grad()
fake_images = generator(Variable(torch.randn(images.size(0), 100)))
g_loss = adversarial_loss(discriminator(fake_images), real_labels)
g_loss.backward()
optimizer_G.step()
if i % 100 == 0:
print('Epoch [{}/{}], Step [{}/{}], d_loss: {:.4f}, g_loss: {:.4f}'
.format(epoch, 200, i, len(train_loader), d_loss.item(), g_loss.item()))
```
在这个示例中,我们使用了 MNIST 数据集训练 GAN,其中生成器网络接受一个随机噪声向量作为输入,生成一张 28x28 的图像。判别器网络接受一张图像作为输入,输出一个值表示该图像是否是真实的。在训练过程中,我们首先训练判别器,让它能够区分真实图像和生成的假图像。然后,我们训练生成器来欺骗判别器,生成尽可能逼真的图像。在这个过程中,我们使用 Adversarial Loss 作为损失函数,它会同时考虑判别器的输出和真实标签,从而鼓励生成器生成更真实的图像。