B站刘二大人-Softmx分类器及MNIST实现-Lecture 9

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系列文章：

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softmax分类器

损失函数：交叉熵

Numpty中实现交叉熵损失函数

Pytorch实现的交叉熵损失

MNIST实现

导包

import torch
from  torch.utils.data import  DataLoader
from torchvision import datasets,transforms
# 使用relu()
import torch.nn.functional as F
# 构造优化器
import  torch.optim as optim

1-准备数据

# 1-准备数据
batch_size = 64
# 将PIL图像抓换为Tensor
transforms = transforms.Compose([transforms.ToTensor(),
                                 transforms.Normalize((0.1307,),(0.3081,))])
train_dataset = datasets.MNIST(root='./datasets/mnist', train=True,
                               transform=transforms,
                               download=False)
test_dataset = datasets.MNIST(root='./datasets/mnist', train=False,
                              transform=transforms,
                              download=False)
train_loader = DataLoader(dataset=train_dataset, batch_size=batch_size,
                          shuffle=True)
test_loader = DataLoader(dataset=test_dataset, batch_size=batch_size,
                         shuffle=False)

2-设计网络模型

# 2-设计网络模型
class Net(torch.nn.Module):
    def __init__(self):
        super(Net, self).__init__()
        self.lay1 = torch.nn.Linear(784,512)
        self.lay2 = torch.nn.Linear(512,256)
        self.lay3 = torch.nn.Linear(256,128)
        self.lay4 = torch.nn.Linear(128,64)
        self.lay5 = torch.nn.Linear(64,10)
    def forward(self,x):

        x = x.view(-1,784)
        x = F.relu(self.lay1(x))
        x = F.relu(self.lay2(x))
        x = F.relu(self.lay3(x))
        x = F.relu(self.lay4(x))
        x = F.relu(self.lay5(x))
        return x

3-构造模型、损失函数、优化器

# 3-构造损失函数与优化器
model = Net()
criterion = torch.nn.CrossEntropyLoss()
optimizer =  torch.optim.SGD(model.parameters(), lr=0.005,momentum=0.5)

4-训练、测试

# 4-训练测试
def train(epoch):
    running_loss = 0.0
    # enumerate(train_loader, 0): batch_idx从0计数
    for batch_idx, data in enumerate(train_loader, 0):
        inputs, target = data
        optimizer.zero_grad()
# forward + backward + update
        outputs = model(inputs)
        loss = criterion(outputs, target)
        loss.backward()
        optimizer.step()
        running_loss += loss.item()
        if(batch_idx % 300 == 299):
            print('[%d, %5d] loss: %.3f'%(epoch + 1, batch_idx + 1, running_loss/300))
            running_loss = 0.0

def test():
    correct = 0
    total = 0
    # 测试不需要生成计算图，不需要梯度更新、反向传播
    with torch.no_grad():
         # data是len =2的list
        # input是data[0], target 是data[1]
        for data in test_loader:
            images, label = data
            outputs = model(images)
            # _ 是返回的最大值， predicted是最大值对应的下标
            _, predicted = torch.max(outputs.data, dim=1)
            total += label.size(0)
            correct += (predicted == label).sum().item()
        print('Accutacy on test set : %d %%'%(100*correct/total))

if __name__ == '__main__':
    for epoch in range(10):
        train(epoch)
        test()

关于：(predicted == label).sum()
会将predicted中的每个元素与对应位置的label进行对边，相同返回True，不同返回False。 .sum求的True的个数

inputs, target = data 说明赋值情况

完整代码

import torch
from  torch.utils.data import  DataLoader
from torchvision import datasets,transforms
# 使用relu()
import torch.nn.functional as F
# 构造优化器
import  torch.optim as optim

# 1-准备数据
batch_size = 64
# 将PIL图像抓换为Tensor
transforms = transforms.Compose([transforms.ToTensor(),
                                 transforms.Normalize((0.1307,),(0.3081,))])
train_dataset = datasets.MNIST(root='./datasets/mnist', train=True,
                               transform=transforms,
                               download=False)
test_dataset = datasets.MNIST(root='./datasets/mnist', train=False,
                              transform=transforms,
                              download=False)
train_loader = DataLoader(dataset=train_dataset, batch_size=batch_size,
                          shuffle=True)
test_loader = DataLoader(dataset=test_dataset, batch_size=batch_size,
                         shuffle=False)

# 2-设计网络模型
class Net(torch.nn.Module):
    def __init__(self):
        super(Net, self).__init__()
        self.lay1 = torch.nn.Linear(784,512)
        self.lay2 = torch.nn.Linear(512,256)
        self.lay3 = torch.nn.Linear(256,128)
        self.lay4 = torch.nn.Linear(128,64)
        self.lay5 = torch.nn.Linear(64,10)
    def forward(self,x):

        x = x.view(-1,784)
        x = F.relu(self.lay1(x))
        x = F.relu(self.lay2(x))
        x = F.relu(self.lay3(x))
        x = F.relu(self.lay4(x))
        x = F.relu(self.lay5(x))
        return x


# 3-构造损失函数与优化器
model = Net()
criterion = torch.nn.CrossEntropyLoss()
optimizer =  torch.optim.SGD(model.parameters(), lr=0.005,momentum=0.5)
# 4-训练测试
def train(epoch):
    running_loss = 0.0
    # enumerate(train_loader, 0): batch_idx从0计数
    for batch_idx, data in enumerate(train_loader, 0):
        inputs, target = data
        optimizer.zero_grad()
# forward + backward + update
        outputs = model(inputs)
        loss = criterion(outputs, target)
        loss.backward()
        optimizer.step()
        running_loss += loss.item()
        if(batch_idx % 300 == 299):
            print('[%d, %5d] loss: %.3f'%(epoch + 1, batch_idx + 1, running_loss/300))
            running_loss = 0.0

def test():
    correct = 0
    total = 0
    # 测试不需要生成计算图，不需要梯度更新、反向传播
    with torch.no_grad():
        for data in test_loader:
            images, label = data
            outputs = model(images)
            # _ 是返回的最大值， predicted是最大值对应的下标
            _, predicted = torch.max(outputs.data, dim=1)
            total += label.size(0)
            correct += (predicted == label).sum().item()
        print('Accutacy on test set : %d %%'%(100*correct/total))

if __name__ == '__main__':
    for epoch in range(10):
        train(epoch)
        test()