Pytorch是torch的python版本，是由Facebook开源的神经网络框架，专门针对 GPU 加速的深度神经网络（DNN）编程。Torch 是一个经典的对多维矩阵数据进行操作的张量
（tensor ）库，在机器学习和其他数学密集型应用有广泛应用。
Pytorch的计算图是动态的，可以根据计算需要实时改变计算图。
由于Torch语言采用 Lua，导致在国内一直很小众，并逐渐被支持 Python 的 Tensorflow 抢走用户。作为经典机器学习库 Torch 的端口，PyTorch 为 Python 语言使用者提供了舒适的写代码选择。

Pytorch是一个基于Python的可续计算包，提供两个高级功能：1、具有强大的GPU加速的张量计算（如NumPy）。2、包含自动求导系统的深度神经网络。

方法一：

找到上图的三种变量，然后.cuda（）便可 

网络模型.cuda（）和损失函数.cuda（）程序如下：

训练数据（输入.cuda（）、标注.cuda（））和 测试数据（输入.cuda（）、标注.cuda（））程序如下：

 电脑内衣GPU可以去Google colab跑程序，设置如下图所示：

 把pycharm的代码复制到Google colab上面去

具体程序如下：

import torch
import torchvision
from torch import nn
from torch.nn import Conv2d, MaxPool2d, Flatten
from torch.utils.tensorboard import SummaryWriter

# from model import *
from torch.utils.data import DataLoader

train_data = torchvision.datasets.CIFAR10(root='./data_CIFAR10',train=True,
                                          transform=torchvision.transforms.ToTensor(),download=True)

test_data = torchvision.datasets.CIFAR10(root='./data_CIFAR10',train=False,
                                          transform=torchvision.transforms.ToTensor(),download=True)

train_data_size = len(train_data)
test_data_size = len(test_data)

print("训练数据集的长度为：{} " .format(train_data_size))
print("测试数据集的长度为：{} " .format(test_data_size))

train_dataloader = DataLoader(train_data,batch_size=64)
test_dataloader = DataLoader(test_data,batch_size=64)

#搭建神经网络

class Tudui(nn.Module):
    def __init__(self):
        super(Tudui, self).__init__()
        self.model1 = nn.Sequential(
            nn.Conv2d(3, 32, 5, padding=2, stride=1),
            nn.MaxPool2d(2),
            nn.Conv2d(32, 32, 5, padding=2, stride=1),
            nn.MaxPool2d(2),
            nn.Conv2d(32, 64, 5, padding=2, stride=1),
            nn.MaxPool2d(2),
            nn.Flatten(),
            nn.Linear(1024, 64),
            nn.Linear(64, 10)
        )

    def forward(self, x):
        x = self.model1(x)
        return x

tudui = Tudui()
# if torch.cuda.is_available():
#     tudui = tudui.cuda()

#损失函数
loss_fn = nn.CrossEntropyLoss()
# if torch.cuda.is_available():
#     loss_fn = loss_fn.cuda()

#优化器
optimizer = torch.optim.SGD(tudui.parameters(),lr=0.01)

#设置训练网络的一些参数
total_train_step = 0
total_test_step = 0
epoch = 10

writer = SummaryWriter('./logs_train')


for i in range(epoch):
    print("------------第 {} 轮训练开始--------------".format(i+1))

    tudui.eval()
    for data in train_dataloader:
        imgs,targets = data
        # if torch.cuda.is_available():
        #     imgs = imgs.cuda()
        #     targets = targets.cuda()

        outputs = tudui(imgs)
        loss = loss_fn(outputs,targets)

        optimizer.zero_grad()
        loss.backward()
        optimizer.step()

        total_train_step +=1
        if total_train_step % 100 ==0:
            print("训练次数 ： {},Loss : {}".format(total_train_step,loss.item()))
            writer.add_scalar("train_loss",loss.item(),total_train_step)

    tudui.eval()
    total_test_loss = 0
    total_accuracy = 0
    with torch.no_grad():
        for data in test_dataloader:
            imgs,targets = data
            # if torch.cuda.is_available():
            #     imgs = imgs.cuda()
            #     targets = targets.cuda()

            outputs = tudui(imgs)
            loss = loss_fn(outputs,targets)
            total_test_loss += loss.item()
            accuracy = (outputs.argmax(1) == targets).sum()
            total_accuracy = total_accuracy +accuracy
    print("整体测试数据集的Loss:{}".format(total_test_loss))
    print("整体测试集上的正确率：{}".format(total_accuracy/test_data_size))
    writer.add_scalar('test_loss',total_test_loss,total_test_step)
    writer.add_scalar("test_accuracy", total_accuracy/test_data_size, total_test_step)
    total_test_step += 1

    torch.save(tudui, 'tudui_{}.pth'.format(i))
    print("模型已保存")
writer.close()

方法二：

 电脑上有多张不同的显卡时，可以用该方法指定模型去哪张显卡运行。具体方法如下：

 device更加常用的写法如下

具体程序如下：

import torch
import torchvision
from torch import nn
from torch.nn import Conv2d, MaxPool2d, Flatten
from torch.utils.tensorboard import SummaryWriter

# from model import *
from torch.utils.data import DataLoader

device = torch.device("cpu")
# device = torch.device("cuda")
# device = torch.device('cuda' if torch.cuda.is_available() else 'cpu')

train_data = torchvision.datasets.CIFAR10(root='./data_CIFAR10',train=True,
                                          transform=torchvision.transforms.ToTensor(),download=True)

test_data = torchvision.datasets.CIFAR10(root='./data_CIFAR10',train=False,
                                          transform=torchvision.transforms.ToTensor(),download=True)

train_data_size = len(train_data)
test_data_size = len(test_data)

print("训练数据集的长度为：{} " .format(train_data_size))
print("测试数据集的长度为：{} " .format(test_data_size))

train_dataloader = DataLoader(train_data,batch_size=64)
test_dataloader = DataLoader(test_data,batch_size=64)

#搭建神经网络

class Tudui(nn.Module):
    def __init__(self):
        super(Tudui, self).__init__()
        self.model1 = nn.Sequential(
            nn.Conv2d(3, 32, 5, padding=2, stride=1),
            nn.MaxPool2d(2),
            nn.Conv2d(32, 32, 5, padding=2, stride=1),
            nn.MaxPool2d(2),
            nn.Conv2d(32, 64, 5, padding=2, stride=1),
            nn.MaxPool2d(2),
            nn.Flatten(),
            nn.Linear(1024, 64),
            nn.Linear(64, 10)
        )

    def forward(self, x):
        x = self.model1(x)
        return x

tudui = Tudui()
tudui = tudui.to(device)
# if torch.cuda.is_available():
#     tudui = tudui.cuda()

#损失函数
loss_fn = nn.CrossEntropyLoss()
loss_fn = loss_fn.to(device)
# if torch.cuda.is_available():
#     loss_fn = loss_fn.cuda()

#优化器
optimizer = torch.optim.SGD(tudui.parameters(),lr=0.01)

#设置训练网络的一些参数
total_train_step = 0
total_test_step = 0
epoch = 10

writer = SummaryWriter('./logs_train')


for i in range(epoch):
    print("------------第 {} 轮训练开始--------------".format(i+1))

    tudui.eval()
    for data in train_dataloader:
        imgs,targets = data
        imgs = imgs.to(device)
        targets = targets.to(device)
        # if torch.cuda.is_available():
        #     imgs = imgs.cuda()
        #     targets = targets.cuda()

        outputs = tudui(imgs)
        loss = loss_fn(outputs,targets)

        optimizer.zero_grad()
        loss.backward()
        optimizer.step()

        total_train_step +=1
        if total_train_step % 100 ==0:
            print("训练次数 ： {},Loss : {}".format(total_train_step,loss.item()))
            writer.add_scalar("train_loss",loss.item(),total_train_step)

    tudui.eval()
    total_test_loss = 0
    total_accuracy = 0
    with torch.no_grad():
        for data in test_dataloader:
            imgs,targets = data
            imgs = imgs.to(device)
            targets = targets.to(device)
            # if torch.cuda.is_available():
            #     imgs = imgs.cuda()
            #     targets = targets.cuda()

            outputs = tudui(imgs)
            loss = loss_fn(outputs,targets)
            total_test_loss += loss.item()
            accuracy = (outputs.argmax(1) == targets).sum()
            total_accuracy = total_accuracy +accuracy
    print("整体测试数据集的Loss:{}".format(total_test_loss))
    print("整体测试集上的正确率：{}".format(total_accuracy/test_data_size))
    writer.add_scalar('test_loss',total_test_loss,total_test_step)
    writer.add_scalar("test_accuracy", total_accuracy/test_data_size, total_test_step)
    total_test_step += 1

    torch.save(tudui, 'tudui_{}.pth'.format(i))
    print("模型已保存")
writer.close()