1. 优化器¶
① 损失函数调用backward方法，就可以调用损失函数的反向传播方法，就可以求出我们需要调节的梯度，我们就可以利用我们的优化器就可以根据梯度对参数进行调整，达到整体误差降低的目的。
② 梯度要清零，如果梯度不清零会导致梯度累加。
2. 神经网络优化一轮¶
In [1]:
import torch
import torchvision
from torch import nn
from torch.nn import Conv2d, MaxPool2d, Flatten, Linear, Sequential
from torch.utils.data import DataLoader
from torch.utils.tensorboard import SummaryWriter
dataset = torchvision.datasets.CIFAR10("./dataset",train=False,transform=torchvision.transforms.ToTensor(),download=True)
dataloader = DataLoader(dataset, batch_size=64,drop_last=True)
class Tudui(nn.Module):
def __init__(self):
super(Tudui, self).__init__()
self.model1 = Sequential(
Conv2d(3,32,5,padding=2),
MaxPool2d(2),
Conv2d(32,32,5,padding=2),
MaxPool2d(2),
Conv2d(32,64,5,padding=2),
MaxPool2d(2),
Flatten(),
Linear(1024,64),
Linear(64,10)
)
def forward(self, x):
x = self.model1(x)
return x
loss = nn.CrossEntropyLoss() # 交叉熵
tudui = Tudui()
optim = torch.optim.SGD(tudui.parameters(),lr=0.01) # 随机梯度下降优化器
for data in dataloader:
imgs, targets = data
outputs = tudui(imgs)
result_loss = loss(outputs, targets) # 计算实际输出与目标输出的差距
optim.zero_grad() # 梯度清零
result_loss.backward() # 反向传播，计算损失函数的梯度
optim.step() # 根据梯度，对网络的参数进行调优
print(result_loss) # 对数据只看了一遍，只看了一轮，所以loss下降不大
Files already downloaded and verified tensor(2.2978, grad_fn=<NllLossBackward0>) tensor(2.2988, grad_fn=<NllLossBackward0>) tensor(2.3163, grad_fn=<NllLossBackward0>) tensor(2.3253, grad_fn=<NllLossBackward0>) tensor(2.2952, grad_fn=<NllLossBackward0>) tensor(2.3066, grad_fn=<NllLossBackward0>) tensor(2.3085, grad_fn=<NllLossBackward0>) tensor(2.3106, grad_fn=<NllLossBackward0>) tensor(2.2960, grad_fn=<NllLossBackward0>) tensor(2.3053, grad_fn=<NllLossBackward0>) tensor(2.2892, grad_fn=<NllLossBackward0>) tensor(2.3090, grad_fn=<NllLossBackward0>) tensor(2.2956, grad_fn=<NllLossBackward0>) tensor(2.3041, grad_fn=<NllLossBackward0>) tensor(2.3012, grad_fn=<NllLossBackward0>) tensor(2.3043, grad_fn=<NllLossBackward0>) tensor(2.2760, grad_fn=<NllLossBackward0>) tensor(2.3051, grad_fn=<NllLossBackward0>) tensor(2.2951, grad_fn=<NllLossBackward0>) tensor(2.3168, grad_fn=<NllLossBackward0>) tensor(2.3140, grad_fn=<NllLossBackward0>) tensor(2.3096, grad_fn=<NllLossBackward0>) tensor(2.2945, 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grad_fn=<NllLossBackward0>) tensor(2.2964, grad_fn=<NllLossBackward0>) tensor(2.2927, grad_fn=<NllLossBackward0>) tensor(2.2941, grad_fn=<NllLossBackward0>) tensor(2.3003, grad_fn=<NllLossBackward0>) tensor(2.2965, grad_fn=<NllLossBackward0>) tensor(2.2908, grad_fn=<NllLossBackward0>) tensor(2.2885, grad_fn=<NllLossBackward0>) tensor(2.2984, grad_fn=<NllLossBackward0>) tensor(2.3009, grad_fn=<NllLossBackward0>) tensor(2.2931, grad_fn=<NllLossBackward0>) tensor(2.2856, grad_fn=<NllLossBackward0>) tensor(2.2907, grad_fn=<NllLossBackward0>) tensor(2.2938, grad_fn=<NllLossBackward0>) tensor(2.2880, grad_fn=<NllLossBackward0>) tensor(2.2975, grad_fn=<NllLossBackward0>) tensor(2.2922, grad_fn=<NllLossBackward0>) tensor(2.2966, grad_fn=<NllLossBackward0>) tensor(2.2804, grad_fn=<NllLossBackward0>)
3. 神经网络优化多轮¶
In [2]:
import torch
import torchvision
from torch import nn
from torch.nn import Conv2d, MaxPool2d, Flatten, Linear, Sequential
from torch.utils.data import DataLoader
from torch.utils.tensorboard import SummaryWriter
dataset = torchvision.datasets.CIFAR10("./dataset",train=False,transform=torchvision.transforms.ToTensor(),download=True)
dataloader = DataLoader(dataset, batch_size=64,drop_last=True)
class Tudui(nn.Module):
def __init__(self):
super(Tudui, self).__init__()
self.model1 = Sequential(
Conv2d(3,32,5,padding=2),
MaxPool2d(2),
Conv2d(32,32,5,padding=2),
MaxPool2d(2),
Conv2d(32,64,5,padding=2),
MaxPool2d(2),
Flatten(),
Linear(1024,64),
Linear(64,10)
)
def forward(self, x):
x = self.model1(x)
return x
loss = nn.CrossEntropyLoss() # 交叉熵
tudui = Tudui()
optim = torch.optim.SGD(tudui.parameters(),lr=0.01) # 随机梯度下降优化器
for epoch in range(20):
running_loss = 0.0
for data in dataloader:
imgs, targets = data
outputs = tudui(imgs)
result_loss = loss(outputs, targets) # 计算实际输出与目标输出的差距
optim.zero_grad() # 梯度清零
result_loss.backward() # 反向传播，计算损失函数的梯度
optim.step() # 根据梯度，对网络的参数进行调优
running_loss = running_loss + result_loss
print(running_loss) # 对这一轮所有误差的总和
Files already downloaded and verified tensor(358.1069, grad_fn=<AddBackward0>) tensor(353.8411, grad_fn=<AddBackward0>) tensor(337.3790, grad_fn=<AddBackward0>) tensor(317.3237, grad_fn=<AddBackward0>) tensor(307.6762, grad_fn=<AddBackward0>) tensor(298.2425, grad_fn=<AddBackward0>) tensor(289.7010, grad_fn=<AddBackward0>) tensor(282.7116, grad_fn=<AddBackward0>) tensor(275.8972, grad_fn=<AddBackward0>) tensor(269.5961, grad_fn=<AddBackward0>) tensor(263.8480, grad_fn=<AddBackward0>) tensor(258.5006, grad_fn=<AddBackward0>) tensor(253.4671, grad_fn=<AddBackward0>) tensor(248.7994, grad_fn=<AddBackward0>) tensor(244.4917, grad_fn=<AddBackward0>) tensor(240.5728, grad_fn=<AddBackward0>) tensor(236.9719, grad_fn=<AddBackward0>) tensor(233.6264, grad_fn=<AddBackward0>) tensor(230.4298, grad_fn=<AddBackward0>) tensor(227.3427, grad_fn=<AddBackward0>)
4. 神经网络学习率优化¶
In [3]:
import torch
import torchvision
from torch import nn
from torch.nn import Conv2d, MaxPool2d, Flatten, Linear, Sequential
from torch.utils.data import DataLoader
from torch.utils.tensorboard import SummaryWriter
dataset = torchvision.datasets.CIFAR10("./dataset",train=False,transform=torchvision.transforms.ToTensor(),download=True)
dataloader = DataLoader(dataset, batch_size=64,drop_last=True)
class Tudui(nn.Module):
def __init__(self):
super(Tudui, self).__init__()
self.model1 = Sequential(
Conv2d(3,32,5,padding=2),
MaxPool2d(2),
Conv2d(32,32,5,padding=2),
MaxPool2d(2),
Conv2d(32,64,5,padding=2),
MaxPool2d(2),
Flatten(),
Linear(1024,64),
Linear(64,10)
)
def forward(self, x):
x = self.model1(x)
return x
loss = nn.CrossEntropyLoss() # 交叉熵
tudui = Tudui()
optim = torch.optim.SGD(tudui.parameters(),lr=0.01) # 随机梯度下降优化器
scheduler = torch.optim.lr_scheduler.StepLR(optim, step_size=5, gamma=0.1) # 每过 step_size 更新一次优化器，更新是学习率为原来的学习率的的 0.1 倍
for epoch in range(20):
running_loss = 0.0
for data in dataloader:
imgs, targets = data
outputs = tudui(imgs)
result_loss = loss(outputs, targets) # 计算实际输出与目标输出的差距
optim.zero_grad() # 梯度清零
result_loss.backward() # 反向传播，计算损失函数的梯度
optim.step() # 根据梯度，对网络的参数进行调优
scheduler.step() # 学习率太小了，所以20个轮次后，相当于没走多少
running_loss = running_loss + result_loss
print(running_loss) # 对这一轮所有误差的总和
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