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利用torch.nn实现前馈神经网络解决 多分类 任务使用至少三种不同的激活函数

2022-03-08 17:46 911 查看

1 导入包

import torch
import numpy as np
import torch.nn as nn
from torch.utils.data import TensorDataset,DataLoader
import torchvision
from IPython import display
from torchvision import transforms

2 加载数据

mnist_train = torchvision.datasets.MNIST(root='./datasets/',download = True,train = True,transform = transforms.ToTensor())
mnist_test = torchvision.datasets.MNIST(root='./datasets/',download = True,train = False,transform = transforms.ToTensor())
batch_size = 256
train_iter = DataLoader(dataset = mnist_train,shuffle = True,batch_size = batch_size)
test_iter = DataLoader(dataset = mnist_test,shuffle = True,batch_size = batch_size)

3 定义平铺层

class FlattenLayer(torch.nn.Module):
def __init__(self):
super(FlattenLayer, self).__init__()
def forward(self, x):
return x.view(x.shape[0],784)

4 模型选择

num_input,num_hidden1,num_hidden2,num_output = 28*28,512,256,10
def choose_model(model_type):
if model_type =='ReLU':
activation = nn.ReLU()
elif model_type =='ELU':
activation = nn.ELU()
else:
activation = nn.Sigmoid()
model = nn.Sequential()
model.add_module("flatten",FlattenLayer())
model.add_module("linear1",nn.Linear(num_input,num_hidden1))
model.add_module("activation",activation)
model.add_module("linear2",nn.Linear(num_hidden1,num_hidden2))
model.add_module("activation",activation)
model.add_module("linear3",nn.Linear(num_hidden2,num_output))
return model
model = choose_model('ReLU')
print(model)

5 参数初始化

# for param in model.parameters():
#     nn.init.normal_(param,mean=0,std=0.001)

for m in model.modules():
if isinstance(m, nn.Linear):
nn.init.xavier_uniform_(m.weight)
nn.init.constant_(m.bias, 0.1)

6 定义训练函数

def train(net,train_iter,test_iter,loss,num_epochs):
train_ls,test_ls,train_acc,test_acc = [],[],[],[]
for epoch in range(num_epochs):
train_ls_sum,train_acc_sum,n = 0,0,0
for x,y in train_iter:
y_pred = net(x)
l = loss(y_pred,y)
optimizer.zero_grad()
l.backward()
optimizer.step()
train_ls_sum +=l.item()
train_acc_sum += (y_pred.argmax(dim = 1)==y).sum().item()
n += y_pred.shape[0]
train_ls.append(train_ls_sum)
train_acc.append(train_acc_sum/n)

test_ls_sum,test_acc_sum,n = 0,0,0
for x,y in test_iter:
y_pred = net(x)
l = loss(y_pred,y)
test_ls_sum +=l.item()
test_acc_sum += (y_pred.argmax(dim = 1)==y).sum().item()
n += y_pred.shape[0]
test_ls.append(test_ls_sum)
test_acc.append(test_acc_sum/n)
print('epoch %d, train_loss %.6f,test_loss %f, train_acc %.6f,test_acc %f'
%(epoch+1, train_ls[epoch],test_ls[epoch], train_acc[epoch],test_acc[epoch]))
return train_ls,test_ls,train_acc,test_acc_sum

7 定义损失函数和优化器

#训练次数和学习率
num_epochs = 20
lr = 0.01
loss  = nn.CrossEntropyLoss()
optimizer = torch.optim.SGD(model.parameters(),lr=lr)

8 模型训练

train_loss,test_loss,train_acc,test_acc = train(model,train_iter,test_iter,loss,num_epochs)

 

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