Pytorch 实验（一） Minist手写数据集测试 1

Minist手写数据集测试

（个人实践笔记，如有纰漏，烦请指出）        

import torch
import torch.nn as nn
import torchvision.datasets as dsets
import torchvision.transforms as transforms

input_size = 28 * 28 # image size of MNIST data
num_classes = 10
num_epochs = 10
batch_size = 100
learning_rate = 1e-3

# MNIST dataset
train_dataset = dsets.MNIST(root = '../../data_sets/mnist', #选择数据的根目录
                           train = True, # 选择训练集
                           transform = transforms.ToTensor(), #转换成tensor变量
                           download = False) # 不从网络上download图片
test_dataset = dsets.MNIST(root = '../../data_sets/mnist', #选择数据的根目录
                           train = False, # 选择训练集
                           transform = transforms.ToTensor(), #转换成tensor变量
                           download = False) # 不从网络上download图片
#加载数据

train_loader = torch.utils.data.DataLoader(dataset = train_dataset, 
                                           batch_size = batch_size, 
                                           shuffle = True)  # 将数据打乱
test_loader = torch.utils.data.DataLoader(dataset = test_dataset,
                                          batch_size = batch_size,
                                          shuffle = True)

class Net(torch.nn.Module):
    def __init__(self,n_input,n_hideen,n_output):
        super(Net,self).__init__()
        self.hidden = torch.nn.Linear(n_input,n_hideen)
        self.output = torch.nn.Linear(n_hideen,n_output)
    def forward(self,x):
        x = F.relu(self.hidden(x))
        x = self.output(x)
        return x
#define the neural net
net = Net(n_input=28*28,n_hideen=100,n_output=10)
optimizer = torch.optim.SGD(net.parameters(),lr = 0.0510)#0.052

loss_func = torch.nn.CrossEntropyLoss()

for i, (images, labels) in enumerate(train_loader): #利用enumerate取出一个可迭代对象的内容
    images = images.reshape(-1, 28*28)
    labels = labels
    
    out = net(images)
    loss = loss_func(out, labels)
    
    optimizer.zero_grad()
    loss.backward()
    optimizer.step()

    if i % 100 == 0:
        print('current loss = %.5f' % loss.item())
with torch.no_grad():
    correct = 0
    total = 0
    for images, labels in test_loader:
        images = images.reshape(-1, 28*28)
        labels = labels
        output_t = net(images)
        _, predicted = torch.max(output_t.data, 1)
        total += labels.size(0)
        correct += (predicted == labels).sum().item()
 
    print('Accuracy of the network on the 10000 test images: {} %'.format(100 * correct / total))
 

运行结果：

current loss = 2.30939
current loss = 1.12731
current loss = 0.61168
current loss = 0.53309
current loss = 0.53291
current loss = 0.51907
Accuracy of the network on the 10000 test images: 90.12 %

运行结果很不稳定，大小在60到90之间波动，自己分析原因可能如下：

1 .  未使用batch_size。

2.   全连接网络，仅一个隐藏层，未加卷积层等。