Pytorch深度学习实践（b站刘二大人）P11讲 (CNN卷积神经网络高级篇)
1.GoogLeNet：
蓝色的块是卷积，红色的块是池化，黄色的是softmax
减少代码冗余：函数/类
当网络结构复杂，对于类似或者相同的子结构，就可以把这个子结构（块）封装成一个类
GoogleNet，常被用作基础主干网络，图中红色圈出的一个部分称为Inception块
2. Inception Module解析
- 卷积核的大小：GoogleNet的下面这个块出发点是不知道多大的卷积核好用，那就在一个块里面把这几种卷积都用一下，然后把它们的结果摞到一起，如果3*3比较好用，自然而然3*3的权重就会比较大
- 提供了几种候选的卷积神经网络的配置，然后在训练中自动的找到最优的卷积组合
- Concatenate 把张量沿着通道拼接在一起（要保证四个通道w h 一样）
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- average pooling 均值池化，设置padding和stride 使得w h 不变
3. 1*1卷积核
1.信息聚合/融合
在上面的网络结构中，使用了多个1*1的卷积核，它的意义是信息的聚合
上图中，使用了1*1卷积核之后，所获得的结果矩阵融合了三个通道的信息。跨越不同通道相同位置元素的值（信息融合）。例如，在考试科目中，计算总分进行比较，也是一种信息聚合。
2.简化计算
1*1卷积核另外一个作用是简化计算量。
如图的网络结构中，使用11卷积核之后，计算量减小到了原来的1/10，主要原因是1*1卷积核能够直接改变通道的数量。
192*28*28经过5*5卷积变成32*28*28需要经过5^2*28^2*192*32， 即5*5的矩阵和单通道里面25个像素进行乘法，所以做一次单通道卷积需要5²，假如用到padding，要对每一个元素进行运算，乘28*28，然后乘通道数192，运算做了32次才能得到输出通道，共120million次
降低运算量：卷积核大小*像素*输入通道*输出通道，1*1卷积变成16*28*28的张量，在通过5*5的卷积变成32*28*28，运算量：1^2*28*28*192*16+5*5*28*28*16*32=12million
有时候把1*1卷积称为network in network
4.inception module 的代码
#第一个分支 池化分支branch——pool
#输出通道24，1*1卷积
self.branch_pool=nn.Conv2d(in_channels,24,kernel_size=1)
#forward
branch_pool=F.avg_pool2d(x,kernel_size=3,stride=1,padding=1)#可以保证average之后大小不变
branch_pool=self.branch_pool(branch_pool)#
#第二个分支branch1x1，1*1分支,16通道,kernel size=1
self.branch1x1=nn.Conv2d(in_channels,16,kernel_size=1)
branch1x1=self.branch1x1(x)
#第三个分支branch5x5分为两个模块， 1*1卷积，5*5，保证图片大小不变padding设成2，通道数输出16、24
self.branch5x5_1=nn.Conv2d(in_channels,16,kernel_size=1)
self.branch5x5_2=nn.Conv2d(16,24,kernel_size=5,padding=2)
branch5x5=self.branch5x5_1(x)
branch5x5=self.branch5x5_2(branch5x5)
#第四个分支branch3x3，分成三块，一个1x1,3x3,3x3
self.branch3x3_1=nn.Conv2d(in_channels,16,kernel_size=1)
self.branch3x3_2=nn.Conv2d(16,24,kernel_size=3,padding=1)
self.branch3x3_3=nn.Conv2d(24,24,kernel_size=3,padding=1)
branch3x3=self.branch3x3_1(x)
branch3x3=self.branch3x3_2(branch3x3)
branch3x3=self.branch3x3_3(branch3x3)
沿着通道数把四个块拼接
#把前面的四个分支放到一个列表里，然后用cat沿着dim=1即batch——size把他们拼起来 （batch——size channel wideth height ）
outputs=[branch1x1,branch5x5,branch3x3,branch_pool]
return torch.cat(outputs.dim=1)Iception全部代码：
#inception block
class InceptionA(nn.Module):
def __init__(self,in_channels):
super(InceptionA,self).__init__()
#in_channels没有写具体的数字为了实例化的时候可以指定输入通道数
#第一层
self.branch_pool=nn.Conv2d(in_channels,16,kernel_size=1)
# 第二层
self.branch5x5_1 = nn.Conv2d(in_channels, 16, kernel_size=1)
self.branch5x5_2 = nn.Conv2d(16, 24, kernel_size=5, padding=2)
# 第三层
self.branch3x3_1 = nn.Conv2d(in_channels, 16, kernel_size=1)
self.branch3x3_2 = nn.Conv2d(16, 24, kernel_size=3, padding=1)
self.branch3x3_3 = nn.Conv2d(24, 24, kernel_size=3, padding=1)
#第四层
self.branch_pool = nn.Conv2d(in_channels, 24, kernel_size=1)
def forward(self,x):
#第一层
branch1x1 = self.branch1x1(x)
#第二层
branch5x5 = self.branch5x5_1(x)
branch5x5 = self.branch5x5_2(branch5x5)
# 第三层
branch3x3 = self.branch3x3_1(x)
branch3x3 = self.branch3x3_2(branch3x3)
branch3x3 = self.branch3x3_3(branch3x3)
# 第四层
branch_pool = F.avg_pool2d(x, kernel_size=3, stride=1, padding=1) # 可以保证average之后大小不变
branch_pool = self.branch_pool(branch_pool)
#cat拼接
outputs = [branch1x1, branch5x5, branch3x3, branch_pool]
return torch.cat(outputs.dim=1)- 用inception写网络
#构造网络
class Net(nn.Module):
def __init__(self):
self.conv1=nn.Conv2d(1,10,kernel_size=5)
#88从inception来，将88降到20
self.conv2 = nn.Conv2d(88,20,kernel_size=5)
self.incep1=InceptionA(in_channels=10)
self.incep2=InceptionA(in_channels=20)
#maxpooling 和全连接
self.mp=nn.MaxPool2d(2)
self.fc=nn.Linear(1408,10)#incep2这一层输出每张图像包含1408个元素
def forward(self,x):
in_size=x.size(0)
#卷积 池化 relu，conv1之后输入通道变成10个
x=F.relu(self.mp(self.conv1(x)))
#incption后输出通道24+16+24+24=88个
x=self.incep1(x)
#conv2之后输出20
x=F.relu(self.mp(self.conv2(x)))
#输出88通道
x = self.incep2(x)
#变成向量
x=x.view(in_size,-1)
#全连接
x=self.fc(x)
return x 
完整代码1：
import torch.nn as nn
import torch
import torch.nn.functional as F
from torchvision import datasets
from torchvision import transforms
from torch.utils.data import DataLoader
import matplotlib.pyplot as plt
batch_size = 64
transform = transforms.Compose([transforms.ToTensor(),
transforms.Normalize((0.1307,), (0.3081,))])
transform = transforms.Compose([transforms.ToTensor(), transforms.Normalize((0.1307,), (0.3081,))])
train_dataset = datasets.MNIST(root='../dataset/mnist/', train=True, transform=transform, download=True)
train_loader = DataLoader(dataset=train_dataset, batch_size=64, shuffle=True)
test_dataset = datasets.MNIST(root='../dataset/mnist/', train=False, transform=transform, download=True)
test_loader = DataLoader(dataset=test_dataset, batch_size=64, shuffle=False)
class InceptionA(torch.nn.Module):
def __init__(self, in_channels):
super(InceptionA, self).__init__()
self.branch_pool = torch.nn.Conv2d(in_channels, 24, kernel_size=1)
self.branch1x1 = torch.nn.Conv2d(in_channels, 16, kernel_size=1)
self.branch5x5_1 = torch.nn.Conv2d(in_channels, 16, kernel_size=1)
self.branch5x5_2 = torch.nn.Conv2d(16, 24, kernel_size=5, padding=2)
self.branch3x3_1 = torch.nn.Conv2d(in_channels, 16, kernel_size=1)
self.branch3x3_2 = torch.nn.Conv2d(16, 24, kernel_size=3, padding=1)
self.branch3x3_3 = torch.nn.Conv2d(24, 24, kernel_size=3, padding=1)
def forward(self, x):
branch1x1 = self.branch1x1(x)
branch5x5 = self.branch5x5_2(self.branch5x5_1(x))
branch3x3 = self.branch3x3_3(self.branch3x3_2(self.branch3x3_1(x)))
branch_pool = F.avg_pool2d(x, kernel_size=3, stride=1, padding=1)
branch_pool = self.branch_pool(branch_pool)
outputs = [branch1x1, branch3x3, branch5x5, branch_pool]
return torch.cat(outputs, dim=1)
class Net(torch.nn.Module):
def __init__(self):
super(Net, self).__init__()
self.conv1 = torch.nn.Conv2d(1, 10, kernel_size=5)
self.conv2 = torch.nn.Conv2d(88, 20, kernel_size=5)
self.incep1 = InceptionA(in_channels=10)
self.incep2 = InceptionA(in_channels=20)
self.mp = nn.MaxPool2d(2)
self.fc = torch.nn.Linear(1408, 10)
def forward(self, x):
in_size = x.size(0)
x = F.relu(self.mp(self.conv1(x)))
x = self.incep1(x)
x = F.relu(self.mp(self.conv2(x)))
x = self.incep2(x)
x = x.view(in_size, -1)
x = self.fc(x)
return x
net = Net()
device = torch.device("cuda:0" if torch.cuda.is_available() else "cpu")
net.to(device)
criterion = torch.nn.CrossEntropyLoss()
optimizer = torch.optim.SGD(net.parameters(), lr=0.01)
def train(epoch):
running_loss = 0.0
for batch_idx, data in enumerate(train_loader, 0):
inputs, targets = data
inputs, targets = inputs.to(device), targets.to(device)
optimizer.zero_grad()
# forward
y_pred = net(inputs)
# backward
loss = criterion(y_pred, targets)
loss.backward()
# update
optimizer.step()
running_loss += loss.item()
if (batch_idx % 300 == 299):
print("[%d,%d]loss:%.3f" % (epoch + 1, batch_idx + 1, running_loss / 300))
running_loss = 0.0
accuracy = []
def test():
correct = 0
total = 0
with torch.no_grad():
for data in test_loader:
images, labels = data
images, labels = images.to(device), labels.to(device)
outputs = net(images)
_, predicted = torch.max(outputs.data, dim=1)
total += labels.size(0)
correct += (labels == predicted).sum().item()
print("accuracy on test set:%d %% [%d/%d]" % (100 * correct / total, correct, total))
accuracy.append(100 * correct / total)
if __name__ == "__main__":
for epoch in range(10):
train(epoch)
test()
plt.plot(range(10), accuracy)
plt.xlabel("epoch")
plt.ylabel("accuracy")
plt.grid()
plt.show()
print("done")
运行结果：
5.ResidualNet残差
梯度消失：因为做的是反向传播，所以要用链式法则把一连串的梯度乘起来，假如每一处的梯度都小于1，不断乘以小于1的值，这个值就会越来越小，趋近于0，w=w-ag;当梯度（g）趋近于0，权重就得不到更新，里输入比较近的这一块没办法得到充分的训练
解决方法：逐层训练，Residual net
残差块实现：
即：
class ResidualBlock(nn.Module):
#Residual Block需要保证输出和输入通道数x一样
def __init__(self,channels):
super(ResidualBlock,self).__init__()
self.channels=channels
#3*3卷积核，保证图像大小不变将padding设为1
#第一个卷积
self.conv1=nn.Conv2d(channels,channels,
kernel_size=3,padding=1)
#第二个卷积
self.conv2=nn.Conv2d(channels,channels,
kernel_size=3,padding=1)
def forward(self,x):
#激活
y=F.relu(self.conv1(x))
y=self.conv2(y)
#先求和 后激活
return F.relu(x+y)
ResidualNet完整代码2
import torch.nn as nn
import torch
import torch.nn.functional as F
from torchvision import datasets
from torchvision import transforms
from torch.utils.data import DataLoader
import matplotlib.pyplot as plt
batch_size = 64
transform = transforms.Compose([transforms.ToTensor(),
transforms.Normalize((0.1307,), (0.3081,))])
transform = transforms.Compose([transforms.ToTensor(), transforms.Normalize((0.1307,), (0.3081,))])
train_dataset = datasets.MNIST(root='../dataset/mnist/', train=True, transform=transform, download=True)
train_loader = DataLoader(dataset=train_dataset, batch_size=64, shuffle=True)
test_dataset = datasets.MNIST(root='../dataset/mnist/', train=False, transform=transform, download=True)
test_loader = DataLoader(dataset=test_dataset, batch_size=64, shuffle=False)
class ResidualBlock(nn.Module):
# Residual Block需要保证输出和输入通道数x一样
def __init__(self, channels):
super(ResidualBlock, self).__init__()
self.channels = channels
# 3*3卷积核，保证图像大小不变将padding设为1
# 第一个卷积
self.conv1 = nn.Conv2d(channels, channels,
kernel_size=3, padding=1)
# 第二个卷积
self.conv2 = nn.Conv2d(channels, channels,
kernel_size=3, padding=1)
def forward(self, x):
# 激活
y = F.relu(self.conv1(x))
y = self.conv2(y)
# 先求和 后激活
return F.relu(x + y)
class Net(torch.nn.Module):
def __init__(self):
super(Net, self).__init__()
self.conv1 = torch.nn.Conv2d(1, 16, kernel_size=5)
self.conv2 = torch.nn.Conv2d(16, 32, kernel_size=5)
self.mp = nn.MaxPool2d(2)
self.rblock1 = ResidualBlock(16)
self.rblock2 = ResidualBlock(32)
self.fc = torch.nn.Linear(512, 10)
def forward(self, x):
in_size = x.size(0)
x = F.relu(self.mp(self.conv1(x)))
x = self.rblock1(x)
x = F.relu(self.mp(self.conv2(x)))
x = self.rblock2(x)
x = x.view(in_size, -1)
x = self.fc(x)
return x
net = Net()
device = torch.device("cuda:0" if torch.cuda.is_available() else "cpu")
net.to(device)
criterion = torch.nn.CrossEntropyLoss()
optimizer = torch.optim.SGD(net.parameters(), lr=0.01)
def train(epoch):
running_loss = 0.0
for batch_idx, data in enumerate(train_loader, 0):
inputs, targets = data
inputs, targets = inputs.to(device), targets.to(device)
optimizer.zero_grad()
# forward
y_pred = net(inputs)
# backward
loss = criterion(y_pred, targets)
loss.backward()
# update
optimizer.step()
running_loss += loss.item()
if (batch_idx % 300 == 299):
print("[%d,%d]loss:%.3f" % (epoch + 1, batch_idx + 1, running_loss / 300))
running_loss = 0.0
accuracy = []
def test():
correct = 0
total = 0
with torch.no_grad():
for data in test_loader:
images, labels = data
images, labels = images.to(device), labels.to(device)
outputs = net(images)
_, predicted = torch.max(outputs.data, dim=1)
total += labels.size(0)
correct += (labels == predicted).sum().item()
print("accuracy on test set:%d %% [%d/%d]" % (100 * correct / total, correct, total))
accuracy.append(100 * correct / total)
if __name__ == "__main__":
for epoch in range(10):
train(epoch)
test()
plt.plot(range(10), accuracy)
plt.xlabel("epoch")
plt.ylabel("accuracy")
plt.grid()
plt.show()
print("done")