pytorch分类问题总结

参考

https://blog.csdn.net/qq_39172845/article/details/123361945

iris数据集

import torch
import pandas as pd
import numpy as np
import matplotlib.pyplot as plt
from sklearn.datasets import load_iris

X,Y=load_iris(return_X_y=True)
# iloc按位置取值
 
print('X.shape:',X.shape)
print('Y.shape:',Y.shape)

from sklearn.model_selection import train_test_split
 
train_X,test_X,train_Y,test_Y = train_test_split(X,Y)
 
# 出现报错，RuntimeError:expected scaler type Long but found Float
# 这是，我们希望目标的数据类型是long tensor(int tensor)，而不是float tensor。
# 目标值是0、1、2这种形式，要求是一个long tensor，64位的整形。
 
# ndarray转换为tensor
train_X = torch.from_numpy(train_X).type(torch.float32)
# train_Y = torch.from_numpy(train_Y).type(torch.float32)
train_Y = torch.from_numpy(train_Y).type(torch.int64)
 
test_X = torch.from_numpy(test_X).type(torch.float32)
# test_Y = torch.from_numpy(test_Y).type(torch.float32)
test_Y = torch.from_numpy(test_Y).type(torch.LongTensor)

from torch.utils.data import TensorDataset
from torch.utils.data import DataLoader
 
batch = 8 #批次大小
 
train_ds = TensorDataset(train_X,train_Y) # Dataset
train_dl = DataLoader(train_ds,batch_size=batch,shuffle=True) # DataLoader
 
test_ds = TensorDataset(test_X,test_Y)
test_dl = DataLoader(test_ds,batch_size=batch) # 对于测试数据没有必要做shuffle

import torch.nn.functional as F
from torch import nn
 
class Model(nn.Module):
    def __init__(self):
        
        #首先要继承父类中所有的变量
        super().__init__()
        
        # 开始初始化所有的层
        self.linear1 = nn.Linear(4,32 ) # 第一个线性层。将输入的4个特征输出到64个特征的隐藏层。
        self.linear2 = nn.Linear(32,32) 
        self.linear3 = nn.Linear(32,3)  # 输出层。因为是三分类，所以输出特征长度为3。
       
    def forward(self,input):
        # forward方法有一个input参数，你的输入是交给forward方法，然后forward方法调用这些层对输入数据处理。
        
        # 线性层1，4 ---> 32
        x1 = F.relu(self.linear1(input))
        
        # 线性层2，32 ---> 32
        x2 =  F.relu(self.linear2(x1))
        
        # 输出层，32 ----> 3
# x3 = F.sigmoid(self.linear3(x2)) # 用这个会有警告
# x3 = torch.sigmoid(self.linear3(x2))
        x3 = self.linear3(x2)
    
        return x3
""" 在输出层，我们不进行激活，因为我们这个是三分类，使用的损失函数是CrossEntropyLoss，它的输入是一个未激活的输出。 它会在函数内部进行一次 ...softmax 进行计算，然后与我们真实的概率分布计算一个损失。 所以在这里面是不需要对预测结果进行激活的。 如果不对预测结果进行激活，一样可以得到输出，使用softmax只是把它映射到了一个长度为1的概率分布上。 如果不激活，输出结果最大的值仍然是概率分布最高的值，也就是肯输出[1,50,2]，虽然没有经过softmax进行激活， 但是它最大值所在的位置就明确指示了预测结果预测是几。 """
model = Model()
model

loss_fn = nn.CrossEntropyLoss() # 使用这个函数来计算softmax概率损失
 
# model(x)的输出是一个长度为3的张量，如何把预测值翻译成实际的预测结果呢？
# iter() 函数用来生成迭代器。next() 函数返回迭代器中的下一项。
input_batch,label_batch = next(iter(train_dl)) # 获得一个批次的数据
 
input_batch.shape # 结果是：torch.Size([8, 4])
label_batch.shape # 结果是：torch.Size([8])
y_pred = model(input_batch) # 返回8个长度为3的张量
y_pred

def accuracy(y_pred,y_true):
    
# y_true=y_true.int()
# y_true=y_true.long()
    y_pred = torch.argmax(y_pred,dim=1)
    
    acc = (y_pred == y_true).float().mean()
    return acc
 
# 我们希望将每一次的epoch中的结果放入列表当中。
train_loss = []
train_acc = []
test_loss = []
test_acc = []
 
epochs = 500
opt = torch.optim.Adam(model.parameters(), lr=0.0001) # Adam优化器
 
for epoch in range(epochs):  # 训练500次
    for x,y in train_dl:
# y = torch.tensor(y,dtype=torch.long)
        y_pred = model(x) # y_pred是经过sigmoid输出的一个介于0~1之间的值
        loss = loss_fn(y_pred,y)
        opt.zero_grad() # 将所有可训练参数的梯度置为0
        loss.backward() # 反向传播
        opt.step() # 优化参数
    with torch.no_grad():
        # 这一部分的计算不需要跟踪计算
        epoch_acc = accuracy(model(train_X),train_Y) #每一个批次，对全部数据进行预测，得到的平均正确率
        epoch_loss = loss_fn(model(train_X),train_Y).data 
        
        epoch_test_acc =  accuracy(model(test_X),test_Y)
        epoch_test_loss = loss_fn(model(test_X),test_Y).data 
        
        # 使用 .item 将单个的tensor输出值转化为了python的标量值
        print("epoch:%d"%epoch)
        print("loss:",round(epoch_loss.item(),3),"，accuracy:",round(epoch_acc.item(),3))
        print("test_loss:",round(epoch_test_loss.item(),3),"，test_accuracy:",round(epoch_test_acc.item(),3))
        print("——————————————————————————————")
        train_loss.append(epoch_loss.item())
        train_acc.append(epoch_acc.item())
        test_loss.append(epoch_test_loss.item())
        test_acc.append(epoch_test_acc.item())

plt.plot(range(1,epochs+1),train_loss,label='train_loss')
plt.plot(range(1,epochs+1),test_loss,label='test_loss')
plt.legend()

结果如下

plt.plot(range(1,epochs+1),train_acc,label='train_acc')
plt.plot(range(1,epochs+1),test_acc,label='test_acc')
plt.legend()

结果如下

load digits训练集和验证集

import torch
import pandas as pd
import numpy as np
import matplotlib.pyplot as plt
from sklearn.datasets import load_digits

X,Y=load_digits(return_X_y=True)
# iloc按位置取值
 
print('X.shape:',X.shape)
print('Y.shape:',Y.shape)

##############Normalization################
X=X/16.0
###########################################

from sklearn.model_selection import train_test_split
 
train_X,test_X,train_Y,test_Y = train_test_split(X,Y)
 
# 出现报错，RuntimeError:expected scaler type Long but found Float
# 这是，我们希望目标的数据类型是long tensor(int tensor)，而不是float tensor。
# 目标值是0、1、2这种形式，要求是一个long tensor，64位的整形。
 
# ndarray转换为tensor
train_X = torch.from_numpy(train_X).type(torch.float32)
# train_Y = torch.from_numpy(train_Y).type(torch.float32)
train_Y = torch.from_numpy(train_Y).type(torch.int64)
 
test_X = torch.from_numpy(test_X).type(torch.float32)
# test_Y = torch.from_numpy(test_Y).type(torch.float32)
test_Y = torch.from_numpy(test_Y).type(torch.LongTensor)


from torch.utils.data import TensorDataset
from torch.utils.data import DataLoader
 
batch = 32 #批次大小
 
train_ds = TensorDataset(train_X,train_Y) # Dataset
train_dl = DataLoader(train_ds,batch_size=batch,shuffle=True) # DataLoader
 
test_ds = TensorDataset(test_X,test_Y)
test_dl = DataLoader(test_ds,batch_size=batch) # 对于测试数据没有必要做shuffle

import torch.nn.functional as F
from torch import nn
 
class Model(nn.Module):
    def __init__(self):
        
        #首先要继承父类中所有的变量
        super().__init__()
        
        # 开始初始化所有的层
        self.linear1 = nn.Linear(64,32) # 第一个线性层。将输入的4个特征输出到64个特征的隐藏层。
        self.linear2 = nn.Linear(32,16) 
        self.linear3 = nn.Linear(16,10)  # 输出层。因为是三分类，所以输出特征长度为3。
       
    def forward(self,input):
        x1 = F.relu(self.linear1(input))
        x2 =  F.relu(self.linear2(x1))
        x3 = self.linear3(x2)
        return x3

model = Model()
print(model)

loss_fn = nn.CrossEntropyLoss() # 使用这个函数来计算softmax概率损失

def accuracy(y_pred,y_true):
    
# y_true=y_true.int()
# y_true=y_true.long()
    y_pred = torch.argmax(y_pred,dim=1)
    
    acc = (y_pred == y_true).float().mean()
    return acc
 
# 我们希望将每一次的epoch中的结果放入列表当中。
train_loss = []
train_acc = []
test_loss = []
test_acc = []
 
epochs = 200
opt = torch.optim.Adam(model.parameters(), lr=0.0001) # Adam优化器
 
for epoch in range(epochs):  # 训练500次
    for x,y in train_dl:
# y = torch.tensor(y,dtype=torch.long)
        y_pred = model(x) # y_pred是经过sigmoid输出的一个介于0~1之间的值
        loss = loss_fn(y_pred,y)
        opt.zero_grad() # 将所有可训练参数的梯度置为0
        loss.backward() # 反向传播
        opt.step() # 优化参数
    with torch.no_grad():
        # 这一部分的计算不需要跟踪计算
        epoch_acc = accuracy(model(train_X),train_Y) #每一个批次，对全部数据进行预测，得到的平均正确率
        epoch_loss = loss_fn(model(train_X),train_Y).data 
        
        epoch_test_acc =  accuracy(model(test_X),test_Y)
        epoch_test_loss = loss_fn(model(test_X),test_Y).data 
        
        # 使用 .item 将单个的tensor输出值转化为了python的标量值
        print("epoch:%d"%epoch)
        print("loss:",round(epoch_loss.item(),3),"，accuracy:",round(epoch_acc.item(),3))
        print("test_loss:",round(epoch_test_loss.item(),3),"，test_accuracy:",round(epoch_test_acc.item(),3))
        print("——————————————————————————————")
        train_loss.append(epoch_loss.item())
        train_acc.append(epoch_acc.item())
        test_loss.append(epoch_test_loss.item())
        test_acc.append(epoch_test_acc.item())
        
fig=plt.figure()
plt.plot(range(1,epochs+1),train_loss,label='train_loss')
plt.plot(range(1,epochs+1),test_loss,label='test_loss')
plt.legend()
plt.show()

fig=plt.figure()
plt.plot(range(1,epochs+1),train_acc,label='train_acc')
plt.plot(range(1,epochs+1),test_acc,label='test_acc')
plt.legend()
plt.show()

load_digits 数据集(仅训练集）

import torch
import pandas as pd
import numpy as np
import matplotlib.pyplot as plt
from sklearn.datasets import load_digits

X,Y=load_digits(return_X_y=True)
# iloc按位置取值
 
print('X.shape:',X.shape)
print('Y.shape:',Y.shape)

##############Normalization################
X=X/16.0
###########################################


# ndarray转换为tensor
train_X = torch.from_numpy(X).type(torch.float32)
# train_Y = torch.from_numpy(train_Y).type(torch.float32)
train_Y = torch.from_numpy(Y).type(torch.int64)

from torch.utils.data import TensorDataset
from torch.utils.data import DataLoader
 
batch = 32 #批次大小
 
train_dataset = TensorDataset(train_X,train_Y) # Dataset
train_dataloader = DataLoader(train_dataset,batch_size=batch,shuffle=True) # DataLoader

import torch.nn.functional as F
from torch import nn
 
class Model(nn.Module):
    def __init__(self):
        
        #首先要继承父类中所有的变量
        super().__init__()
        
        # 开始初始化所有的层
        self.linear1 = nn.Linear(64,32) # 第一个线性层。将输入的4个特征输出到64个特征的隐藏层。
        self.linear2 = nn.Linear(32,16) 
        self.linear3 = nn.Linear(16,10)  # 输出层。因为是三分类，所以输出特征长度为3。
       
    def forward(self,input):
        x1 = F.relu(self.linear1(input))
        x2 =  F.relu(self.linear2(x1))
        x3 = self.linear3(x2)
        return x3

model = Model()
print(model)

loss_fn = nn.CrossEntropyLoss() # 使用这个函数来计算softmax概率损失

def accuracy(y_pred,y_true):
    
# y_true=y_true.int()
# y_true=y_true.long()
    y_pred = torch.argmax(y_pred,dim=1)
    
    acc = (y_pred == y_true).float().mean()
    return acc
 

train_loss = []
train_acc = []
 
epochs = 200
opt = torch.optim.Adam(model.parameters(), lr=0.0001) # Adam优化器
 
for epoch in range(epochs):  # 训练500次
    for x,y in train_dataloader:
# y = torch.tensor(y,dtype=torch.long)
        y_pred = model(x) # y_pred是经过sigmoid输出的一个介于0~1之间的值
        loss = loss_fn(y_pred,y)
        opt.zero_grad() # 将所有可训练参数的梯度置为0
        loss.backward() # 反向传播
        opt.step() # 优化参数
    with torch.no_grad():
        # 这一部分的计算不需要跟踪计算
        epoch_acc = accuracy(model(train_X),train_Y) #每一个批次，对全部数据进行预测，得到的平均正确率
        epoch_loss = loss_fn(model(train_X),train_Y).data 
        
        # 使用 .item 将单个的tensor输出值转化为了python的标量值
        print("epoch:%d"%epoch)
        print("loss:",round(epoch_loss.item(),3),"，accuracy:",round(epoch_acc.item(),3))
        print("——————————————————————————————")
        train_loss.append(epoch_loss.item())
        train_acc.append(epoch_acc.item())
        
fig=plt.figure()
plt.plot(range(1,epochs+1),train_loss,label='train_loss')
plt.legend()
plt.show()

fig=plt.figure()
plt.plot(range(1,epochs+1),train_acc,label='train_acc')
plt.legend()
plt.show()

mnist数据集

参考
https://nextjournal.com/gkoehler/pytorch-mnist

import torch
import torchvision

n_epochs = 3
batch_size_train = 64
batch_size_test = 1000
learning_rate = 0.01
momentum = 0.5
log_interval = 10

random_seed = 1
torch.backends.cudnn.enabled = False
torch.manual_seed(random_seed)


train_loader = torch.utils.data.DataLoader(
  torchvision.datasets.MNIST('/Users/xiaokangyu/Desktop/dataset/DL/MNIST_digit/', train=True, download=False,
                             transform=torchvision.transforms.Compose([
                               torchvision.transforms.ToTensor(),
                               torchvision.transforms.Normalize(
                                 (0.1307,), (0.3081,))
                             ])),
  batch_size=batch_size_train, shuffle=True)

test_loader = torch.utils.data.DataLoader(
  torchvision.datasets.MNIST('/Users/xiaokangyu/Desktop/dataset/DL/MNIST_digit/', train=False, download=False,
                             transform=torchvision.transforms.Compose([
                               torchvision.transforms.ToTensor(),
                               torchvision.transforms.Normalize(
                                 (0.1307,), (0.3081,))
                             ])),
  batch_size=batch_size_test, shuffle=True)

examples = enumerate(test_loader)
batch_idx, (example_data, example_targets) = next(examples)
print(example_data.shape)

import matplotlib.pyplot as plt

fig = plt.figure()
for i in range(6):
    plt.subplot(2,3,i+1)
    plt.tight_layout()
    plt.imshow(example_data[i][0], cmap='gray', interpolation='none')
    plt.title("Ground Truth: {}".format(example_targets[i]))
    plt.xticks([])
    plt.yticks([])
plt.show()

import torch.nn as nn
import torch.nn.functional as F
import torch.optim as optim

class Net(nn.Module):
    def __init__(self):
        super(Net, self).__init__()
        self.conv1 = nn.Conv2d(1, 10, kernel_size=5)
        self.conv2 = nn.Conv2d(10, 20, kernel_size=5)
        self.conv2_drop = nn.Dropout2d()
        self.fc1 = nn.Linear(320, 50)
        self.fc2 = nn.Linear(50, 10)

    def forward(self, x):
        x = F.relu(F.max_pool2d(self.conv1(x), 2))
        x = F.relu(F.max_pool2d(self.conv2_drop(self.conv2(x)), 2))
        x = x.view(-1, 320)
        x = F.relu(self.fc1(x))
        x = F.dropout(x, training=self.training)
        x = self.fc2(x)
        return F.log_softmax(x)
    
network = Net()
optimizer = optim.SGD(network.parameters(), lr=learning_rate,
                      momentum=momentum)

train_losses = []
train_counter = []
test_losses = []
test_counter = [i*len(train_loader.dataset) for i in range(n_epochs + 1)]

def train(epoch):
    network.train()
    for batch_idx, (data, target) in enumerate(train_loader):
        optimizer.zero_grad()
        output = network(data)
        loss = F.nll_loss(output, target)
        loss.backward()
        optimizer.step()
        if batch_idx % log_interval == 0:
            print('Train Epoch: {} [{}/{} ({:.0f}%)]\tLoss: {:.6f}'.format(
            epoch, batch_idx * len(data), len(train_loader.dataset),
            100. * batch_idx / len(train_loader), loss.item()))
            train_losses.append(loss.item())
            train_counter.append(
            (batch_idx*64) + ((epoch-1)*len(train_loader.dataset)))
            torch.save(network.state_dict(), './results/model.pth')
            torch.save(optimizer.state_dict(), './results/optimizer.pth')
            
def test():
    network.eval()
    test_loss = 0
    correct = 0
    with torch.no_grad():
        for data, target in test_loader:
            output = network(data)
            test_loss += F.nll_loss(output, target, size_average=False).item()
            pred = output.data.max(1, keepdim=True)[1]
            correct += pred.eq(target.data.view_as(pred)).sum()
    test_loss /= len(test_loader.dataset)
    test_losses.append(test_loss)
    print('\nTest set: Avg. loss: {:.4f}, Accuracy: {}/{} ({:.0f}%)\n'.format(
    test_loss, correct, len(test_loader.dataset),
    100. * correct / len(test_loader.dataset)))
    
test()
for epoch in range(1, n_epochs + 1):
    train(epoch)
    test()
    
fig = plt.figure()
plt.plot(train_counter, train_losses, color='blue')
plt.scatter(test_counter, test_losses, color='red')
plt.legend(['Train Loss', 'Test Loss'], loc='upper right')
plt.xlabel('number of training examples seen')
plt.ylabel('negative log likelihood loss')
fig

with torch.no_grad():
    output = network(example_data)
    
fig = plt.figure()
for i in range(6):
    plt.subplot(2,3,i+1)
    plt.tight_layout()
    plt.imshow(example_data[i][0], cmap='gray', interpolation='none')
    plt.title("Prediction: {}".format(
        output.data.max(1, keepdim=True)[1][i].item()))
    plt.xticks([])
    plt.yticks([])
fig

重新加载训练

continued_network = Net()
continued_optimizer = optim.SGD(network.parameters(), lr=learning_rate,
                                momentum=momentum)

model_pth='./results/model.pth'
optimizer_pth='./results/optimizer.pth'
network_state_dict = torch.load(model_pth)
continued_network.load_state_dict(network_state_dict)

optimizer_state_dict = torch.load(optimizer_pth)
continued_optimizer.load_state_dict(optimizer_state_dict)

for i in range(4,9):
    test_counter.append(i*len(train_loader.dataset))
    train(i)
    test()

fig = plt.figure()
plt.plot(train_counter, train_losses, color='blue')
plt.scatter(test_counter, test_losses, color='red')
plt.legend(['Train Loss', 'Test Loss'], loc='upper right')
plt.xlabel('number of training examples seen')
plt.ylabel('negative log likelihood loss')
fig

mnist训练集和测试集

import torch
import pandas as pd
import numpy as np
import matplotlib.pyplot as plt
import torch
import pandas as pd
import numpy as np
import matplotlib.pyplot as plt

data=np.load("/Users/xiaokangyu/Desktop/dataset/DL/MNIST_digit/mnist.npz")
print(data["x_train"].shape) # (60000, 28, 28)
print(data["y_train"].shape) # (60000,)
print(data["x_test"].shape)  # (10000, 28, 28)
print(data["y_test"].shape)  # (10000,)

x_train=data["x_train"]
y_train=data["y_train"]
x_test =data["x_test"]
y_test =data["y_test"]

x_train=x_train.reshape(x_train.shape[0],-1) #reshape
x_test=x_test.reshape(x_test.shape[0],-1) #reshape
########## 最简单的标准化############
x_train=x_train/255.0
x_test=x_test/255.0  
########## 最简单的标准化############
print(x_train.shape)
print(x_test.shape)


train_X=x_train.copy()
train_Y=y_train.copy()
test_X=x_test.copy()
test_Y=y_test.copy()
# from sklearn.model_selection import train_test_split
 
# train_X,test_X,train_Y,test_Y = train_test_split(X,Y)
 
# 出现报错，RuntimeError:expected scaler type Long but found Float
# 这是，我们希望目标的数据类型是long tensor(int tensor)，而不是float tensor。
# 目标值是0、1、2这种形式，要求是一个long tensor，64位的整形。
 
# ndarray转换为tensor
train_X = torch.from_numpy(train_X).type(torch.float32)
# train_Y = torch.from_numpy(train_Y).type(torch.float32)
train_Y = torch.from_numpy(train_Y).type(torch.int64)
 
test_X = torch.from_numpy(test_X).type(torch.float32)
# test_Y = torch.from_numpy(test_Y).type(torch.float32)
test_Y = torch.from_numpy(test_Y).type(torch.LongTensor)


from torch.utils.data import TensorDataset
from torch.utils.data import DataLoader
 
batch = 128 #批次大小
 
train_ds = TensorDataset(train_X,train_Y) # Dataset
train_dl = DataLoader(train_ds,batch_size=batch,shuffle=True) # DataLoader
 
test_ds = TensorDataset(test_X,test_Y)
test_dl = DataLoader(test_ds,batch_size=batch) # 对于测试数据没有必要做shuffle

import torch.nn.functional as F
from torch import nn

class Model(nn.Module):
    def __init__(self):
        
        #首先要继承父类中所有的变量
        super().__init__()
        
        # 开始初始化所有的层
        self.linear1 = nn.Linear(784,256) # 不要写成768，我也不知道为啥我脑袋里会出现这个数字，可能是28*28我记错了
        self.linear2 = nn.Linear(256,64) 
        self.linear3 = nn.Linear(64,10)  # 输出层。因为是三分类，所以输出特征长度为3。
       
    def forward(self,input):
        x1 = F.relu(self.linear1(input))
        x2 =  F.relu(self.linear2(x1))
        x3 = self.linear3(x2)
        return x3

model = Model()
print(model)

loss_fn = nn.CrossEntropyLoss() # 使用这个函数来计算softmax概率损失

def accuracy(y_pred,y_true):
    
# y_true=y_true.int()
# y_true=y_true.long()
    y_pred = torch.argmax(y_pred,dim=1)
    
    acc = (y_pred == y_true).float().mean()
    return acc
 
# 我们希望将每一次的epoch中的结果放入列表当中。
train_loss = []
train_acc = []
test_loss = []
test_acc = []
 
epochs = 20
opt = torch.optim.Adam(model.parameters(), lr=0.001) # Adam优化器
 
for epoch in range(epochs):  # 训练500次
    for x,y in train_dl:
# y = torch.tensor(y,dtype=torch.long)
        y_pred = model(x) # y_pred是经过sigmoid输出的一个介于0~1之间的值
        loss = loss_fn(y_pred,y)
        opt.zero_grad() # 将所有可训练参数的梯度置为0
        loss.backward() # 反向传播
        opt.step() # 优化参数
    with torch.no_grad():
        # 这一部分的计算不需要跟踪计算
        epoch_acc = accuracy(model(train_X),train_Y) #每一个批次，对全部数据进行预测，得到的平均正确率
        epoch_loss = loss_fn(model(train_X),train_Y).data 
        
        epoch_test_acc =  accuracy(model(test_X),test_Y)
        epoch_test_loss = loss_fn(model(test_X),test_Y).data 
        
        # 使用 .item 将单个的tensor输出值转化为了python的标量值
        print("epoch:%d"%epoch)
        print("loss:",round(epoch_loss.item(),3),"，accuracy:",round(epoch_acc.item(),3))
        print("test_loss:",round(epoch_test_loss.item(),3),"，test_accuracy:",round(epoch_test_acc.item(),3))
        print("——————————————————————————————")
        train_loss.append(epoch_loss.item())
        train_acc.append(epoch_acc.item())
        test_loss.append(epoch_test_loss.item())
        test_acc.append(epoch_test_acc.item())
        
fig=plt.figure()
plt.plot(range(1,epochs+1),train_loss,label='train_loss')
plt.plot(range(1,epochs+1),test_loss,label='test_loss')
plt.legend()
plt.show()

fig=plt.figure()
plt.plot(range(1,epochs+1),train_acc,label='train_acc')
plt.plot(range(1,epochs+1),test_acc,label='test_acc')
plt.legend()
plt.show()

mnist仅训练集

import torch
import pandas as pd
import numpy as np
import matplotlib.pyplot as plt


import numpy as np 
data=np.load("/Users/xiaokangyu/Desktop/dataset/DL/MNIST_digit/mnist.npz")
print(data["x_train"].shape) # (60000, 28, 28)
print(data["y_train"].shape) # (60000,)
print(data["x_test"].shape)  # (10000, 28, 28)
print(data["y_test"].shape)  # (10000,)

x_train=data["x_train"]
y_train=data["y_train"]
x_test =data["x_test"]
y_test =data["y_test"]

x_train=x_train.reshape(x_train.shape[0],-1) #reshape
x_test=x_test.reshape(x_test.shape[0],-1) #reshape
########## 最简单的标准化############
x_train=x_train/255.0
x_test=x_test/255.0  
########## 最简单的标准化############
print(x_train.shape)
print(x_test.shape)


X=x_train.copy()
Y=y_train.copy()
# ndarray转换为tensor
train_X = torch.from_numpy(X).type(torch.float32)
# train_Y = torch.from_numpy(train_Y).type(torch.float32)
train_Y = torch.from_numpy(Y).type(torch.int64)

from torch.utils.data import TensorDataset
from torch.utils.data import DataLoader
 
batch = 128 #批次大小
 
train_dataset = TensorDataset(train_X,train_Y) # Dataset
train_dataloader = DataLoader(train_dataset,batch_size=batch,shuffle=True) # DataLoader

import torch.nn.functional as F
from torch import nn
 
class Model(nn.Module):
    def __init__(self):
        
        #首先要继承父类中所有的变量
        super().__init__()
        
        # 开始初始化所有的层
        self.linear1 = nn.Linear(784,256) # 不要写成768，我也不知道为啥我脑袋里会出现这个数字，可能是28*28我记错了
        self.linear2 = nn.Linear(256,64) 
        self.linear3 = nn.Linear(64,10)  # 输出层。因为是三分类，所以输出特征长度为3。
       
    def forward(self,input):
        x1 = F.relu(self.linear1(input))
        x2 =  F.relu(self.linear2(x1))
        x3 = self.linear3(x2)
        return x3

model = Model()
print(model)

loss_fn = nn.CrossEntropyLoss() # 使用这个函数来计算softmax概率损失

def accuracy(y_pred,y_true):
    
# y_true=y_true.int()
# y_true=y_true.long()
    y_pred = torch.argmax(y_pred,dim=1)
    
    acc = (y_pred == y_true).float().mean()
    return acc
 

train_loss = []
train_acc = []
 
epochs = 10
opt = torch.optim.Adam(model.parameters(), lr=0.001) # Adam优化器
 
for epoch in range(epochs):  # 训练500次
    for x,y in train_dataloader:
# y = torch.tensor(y,dtype=torch.long)
        y_pred = model(x) # y_pred是经过sigmoid输出的一个介于0~1之间的值
        loss = loss_fn(y_pred,y)
        opt.zero_grad() # 将所有可训练参数的梯度置为0
        loss.backward() # 反向传播
        opt.step() # 优化参数
    with torch.no_grad():
        # 这一部分的计算不需要跟踪计算
        epoch_acc = accuracy(model(train_X),train_Y) #每一个批次，对全部数据进行预测，得到的平均正确率
        epoch_loss = loss_fn(model(train_X),train_Y).data 
        
        # 使用 .item 将单个的tensor输出值转化为了python的标量值
        print("epoch:%d"%epoch)
        print("loss:",round(epoch_loss.item(),3),"，accuracy:",round(epoch_acc.item(),3))
        print("——————————————————————————————")
        train_loss.append(epoch_loss.item())
        train_acc.append(epoch_acc.item())
        
fig=plt.figure()
plt.plot(range(1,epochs+1),train_loss,label='train_loss')
plt.legend()
plt.show()

fig=plt.figure()
plt.plot(range(1,epochs+1),train_acc,label='train_acc')
plt.legend()
plt.show()

结果如下

温馨提示

我应用到别的数据集时，出了一个很小的问题，就是一定要注意标签Y的类型，我当时没注意用的是int8，结果就报错了
正确的用法是

train_Y = torch.from_numpy(train_Y).type(torch.int64)

不管你原始的Y是什么类型，最终输入到crossentropy函数中计算的，一定要提前转换成torch.int64类型，否则报错