pytorch优化器

优化器optimizer加速神经网络的训练

SGD方法（Stochestic Gradient Descent）（随机梯度下降）每次使用批量数据训练，虽然不能反映整体情况，但是加速了训练速度，也不会丢失很多的准确度。

其他方法参考：Optimizer

import numpy as np
import torch
import torch.utils.data as Data
import torch.nn.functional as F
import matplotlib.pyplot as plt
from torch.autograd import Variable



#给一些超参数
LR = 0.01
BATCH_SIZE = 32
EPOCH = 12

x = torch.unsqueeze(torch.linspace(-1,1,1000),dim = 1)
y = x.pow(2) + 0.1*torch.normal(torch.zeros(*x.size()))

#plot dataset
plt.scatter(x.numpy(),y.numpy())
plt.show()

打印数据点看一下数据

import numpy as np
import torch
import torch.utils.data as Data
import torch.nn.functional as F
import matplotlib.pyplot as plt
from torch.autograd import Variable



#给一些超参数
LR = 0.01
BATCH_SIZE = 32
EPOCH = 12

x = torch.unsqueeze(torch.linspace(-1,1,1000),dim = 1)
y = x.pow(2) + 0.1*torch.normal(torch.zeros(*x.size()))

##plot dataset
#plt.scatter(x.numpy(),y.numpy())
#plt.show()

torch_dataset = Data.TensorDataset(x,y)
loader = Data.DataLoader(dataset = torch_dataset,batch_size = BATCH_SIZE,shuffle = True)


#构建神经网络
class Net(torch.nn.Module): #从Module模块继承
    #定义阶段
    def __init__(self,n_feature,n_hidden,n_output):
        super(Net,self).__init__() #继承Net到模块
        self.hidden = torch.nn.Linear(n_feature,n_hidden)#隐藏层
        self.predict = torch.nn.Linear(n_hidden,n_output)#输出层
    #搭建神经网络过程
    def forward(self,x):#神经网络前向传递的过程
        x = F.relu(self.hidden(x))
        x = self.predict(x) #在输出的时候不用激励函数，因为用激励还输会截断一部分值的数据
        return x

#用四个不同的优化器优化神经网络
net_SGD =      Net(1,20,1)
net_Momentum = Net(1,20,1)
net_RMSprop =  Net(1,20,1)
net_Adam =     Net(1,20,1)

nets = [net_SGD,net_Momentum,net_RMSprop,net_Adam]

opt_SGD = torch.optim.SGD(net_SGD.parameters(),lr = LR)
opt_Momentum = torch.optim.SGD(net_Momentum.parameters(),lr = LR,momentum = 0.8)
opt_RMSprop     = torch.optim.RMSprop(net_RMSprop.parameters(), lr=LR, alpha=0.9)
opt_Adam        = torch.optim.Adam(net_Adam.parameters(), lr=LR, betas=(0.9, 0.99))

optimizers = [opt_SGD, opt_Momentum, opt_RMSprop, opt_Adam]

loss_func = torch.nn.MSELoss()
losses_his = [[],[],[],[]] #记录每个优化器的误差变化

for epoch in range(EPOCH):
    print('Epoch: ', epoch)
    for step, (batch_x, batch_y) in enumerate(loader):
        b_x = Variable(batch_x) #这里的batch_x都是tensor的形式，要Variable一下才能变成Variable
        b_y = Variable(batch_y)
        
        # 对每个优化器, 优化属于他的神经网络
        for net, opt, l_his in zip(nets, optimizers, losses_his):
            output = net(b_x)              # get output for every net
            loss = loss_func(output, b_y)  # compute loss for every net
            opt.zero_grad()                # clear gradients for next train
            loss.backward()                # backpropagation, compute gradients
            opt.step()                     # apply gradients
            l_his.append(loss.data.numpy())     # loss recoder
            
            
labels = ['SGD','Momentum','RMSprop','Adam']

for i,l_his in enumerate(losses_his):
    plt.plot(l_his,label = labels[i])

plt.legend(loc = 'best')
plt.xlabel('Steps')
plt.ylabel('Loss')
plt.ylim((0,0.2))
plt.show()

Momentum比SGD更快一点