Pytorch学习笔记9——AutoEncoder

Pytorch学习笔记9——AutoEncoder

非监督学习的作用：
1.降维
2.预处理
3.可视化
4.利用无监督标签
5.压缩，超分辨率，降噪

对抗自编码器：

中间变量变成一个分布：

KL divergence:
直观理解：





此时autoencoder获得的中间hidden vector不是一个具体的vector，而是一个分布，我们需要再sample一个vector x出来

怎么backpropogation？取出分布（sample）过程不可微分：

把对z的sample过程转变为计算过程：
z=μ+σe

加入KL divergence的regularization效果：
Loss+βKL(q,p)
如果没有regularization，网络就可以通过学习一个很narrow的distribution来骗过test（数据集中，loss低），有的话，得到的分布越接近正态分布总loss越低，迫使学习到的分布趋近于均值为0的正态分布。


VAE: variational auto encoder:用分布代替确定的序列数值。



KL divergence,当p为正态分布时：

AE与VAE实战代码：
AE:

import torch
from torch import nn

class AE(nn.Module):

    def __init__(self):
        super(AE,self).__init__()
        #[b,784]
        self.encoder=nn.Sequential(
            nn.Linear(784,256),
            nn.ReLU(),
            nn.Linear(256,64),
            nn.ReLU(),
            nn.Linear(64,20),
            nn.ReLU()
        )
        #[b,20]=>[b,784]
        self.decoder=nn.Sequential(
            nn.Linear(20,64),
            nn.ReLU(),
            nn.Linear(64,256),
            nn.ReLU(),
            nn.Linear(256,784),
            nn.Sigmoid()
        )

    def forward(self,x):
        '''

        :param x: [b,1,28,28]
        :return:
        '''
        batchsz=x.size(0)
        #flatten
        x=x.view(batchsz,784)
        x=self.encoder(x)
        x=self.decoder(x)
        #RESHAPE
        x=x.view(batchsz,1,28,28)
        return x

MAIN:

import torch
from torch.utils.data import DataLoader
from torchvision import transforms,datasets
from torch import nn,optim
from pytorch2.AE import AE
import visdom
if __name__=='__main__':
    mnist_train=datasets.MNIST('mnist',True,transform=transforms.Compose([
        transforms.ToTensor()]),download=True)
    mnist_train=DataLoader(mnist_train,batch_size=32,shuffle=True)

    mnist_test=datasets.MNIST('mnist',False,transform=transforms.Compose([
        transforms.ToTensor()]),download=True)
    mnist_train=DataLoader(mnist_test,batch_size=32,shuffle=True)

    x=iter(mnist_train).next()
    print('x:',x.shape)

    device=torch.device('cuda')
    model=AE().to(device)
    criteon=nn.MSELoss()
    optimizer=optim.Adam(model.parameters(),lr=1e-3)
    print(model)
    viz=visdom.Visdom()
    for epoch in range(1000):
        for batchidx,(x,_) in enumerate(mnist_train):
           #[b,1,28,28]
            x=x.to(device)
            x_hat=model(x)
            loss=criteon(x_hat,x)#x是输入图像，x_hat是得到的输出图像
        #backpropogation
            optimizer.zero_grad()
            loss.backward()
            optimizer.step()

        print(epoch,'loss:',loss.item)
        x,_=iter(mnist_test).next()
        x=x.to(device)
        with torch.no_grad():
            x_hat=model(x)
        viz.images(x,nrow=8,win='x',opts=dict(title='x'))
        viz.images(x_hat,nrow=8,win='x_hat',opts=dict(title='x_hat'))

VAE:

import numpy as np
import torch
from torch import nn

class VAE(nn.Module):

    def __init__(self):
        super(VAE,self).__init__()
        #[b,784]
        #u:[b,10]
        #sigma:[b,10]
        self.encoder=nn.Sequential(
            nn.Linear(784,256),
            nn.ReLU(),
            nn.Linear(256,64),
            nn.ReLU(),
            nn.Linear(64,20),
            nn.ReLU()
        )
        #[b,20]=>[b,784]
        self.decoder=nn.Sequential(
            nn.Linear(10,64),
            nn.ReLU(),

MAIN2：

import torch
from torch.utils.data import DataLoader
from torchvision import transforms,datasets
from torch import nn,optim
from pytorch2.AE import AE
import visdom
if __name__=='__main__':
    mnist_train=datasets.MNIST('mnist',True,transform=transforms.Compose([
        transforms.ToTensor()]),download=True)
    mnist_train=DataLoader(mnist_train,batch_size=32,shuffle=True)

    mnist_test=datasets.MNIST('mnist',False,transform=transforms.Compose([
        transforms.ToTensor()]),download=True)
    mnist_train=DataLoader(mnist_test,batch_size=32,shuffle=True)

    x=iter(mnist_train).next()
    print('x:',x.shape)

    device=torch.device('cuda')
    model=AE().to(device)
    criteon=nn.MSELoss()
    optimizer=optim.Adam(model.parameters(),lr=1e-3)
    print(model)
    viz=visdom.Visdom()
    for epoch in range(1000):
        for batchidx,(x,_) in enumerate(mnist_train):
           #[b,1,28,28]
            x=x.to(device)
            x_hat,kld=model(x)
            loss=criteon(x_hat,x)#x是输入图像，x_hat是得到的输出图像

            if kld is not None:
               elbo=-loss-1.0*kld
               loss=-elbo
            # backpropogation
            optimizer.zero_grad()
            loss.backward()
            optimizer.step()

        print(epoch,'loss:',loss.item,'kld:',kld)
        x,_=iter(mnist_test).next()
        x=x.to(device)
        with torch.no_grad():
            x_hat=model(x)
        viz.images(x,nrow=8,win='x',opts=dict(title='x'))
        viz.images(x_hat,nrow=8,win='x_hat',opts=dict(title='x_hat'))