在公开数据训练了模型，有时候需要拿到自己的数据上微调。今天正好做了一下微调，在此记录一下微调的方法。用Pytorch还是比较容易实现的。
网上找了很多方法，以及Chatgpt也给了很多方法，但是不够简洁和容易理解。
大体步骤是：
1、加载训练好的模型。
2、冻结不想微调的层，设置想训练的层。（这里可以新建一个层替换原有层，也可以不新建层，直接微调原有层）
3、训练即可。
1、先加载一个模型
我这里是训练好的一个SqueezeNet模型，所有模型都适用。
## 加载要微调的模型
# 环境里必须有模型的框架，才能torch.load
from Model.main_SqueezeNet import SqueezeNet,Firemodel = torch.load("Model/SqueezeNet.pth").to(device)
print(model)
# 输出结果
SqueezeNet((stem): Sequential((0): Conv2d(1, 8, kernel_size=(3, 3), stride=(1, 1), padding=(1, 1))(1): BatchNorm2d(8, eps=1e-05, momentum=0.1, affine=True, track_running_stats=True)(2): ReLU(inplace=True)(3): MaxPool2d(kernel_size=2, stride=2, padding=0, dilation=1, ceil_mode=False))(fire2): Fire((squeeze): Sequential((0): Conv2d(8, 4, kernel_size=(1, 1), stride=(1, 1))(1): BatchNorm2d(4, eps=1e-05, momentum=0.1, affine=True, track_running_stats=True)(2): ReLU(inplace=True))(expand_1x1): Sequential((0): Conv2d(4, 8, kernel_size=(1, 1), stride=(1, 1))(1): BatchNorm2d(8, eps=1e-05, momentum=0.1, affine=True, track_running_stats=True)(2): ReLU(inplace=True))(expand_3x3): Sequential((0): Conv2d(4, 8, kernel_size=(3, 3), stride=(1, 1), padding=(1, 1))(1): BatchNorm2d(8, eps=1e-05, momentum=0.1, affine=True, track_running_stats=True)(2): ReLU(inplace=True)))(fire3): Fire((squeeze): Sequential((0): Conv2d(16, 8, kernel_size=(1, 1), stride=(1, 1))(1): BatchNorm2d(8, eps=1e-05, momentum=0.1, affine=True, track_running_stats=True)(2): ReLU(inplace=True))(expand_1x1): Sequential((0): Conv2d(8, 8, kernel_size=(1, 1), stride=(1, 1))(1): BatchNorm2d(8, eps=1e-05, momentum=0.1, affine=True, track_running_stats=True)(2): ReLU(inplace=True))(expand_3x3): Sequential((0): Conv2d(8, 8, kernel_size=(3, 3), stride=(1, 1), padding=(1, 1))(1): BatchNorm2d(8, eps=1e-05, momentum=0.1, affine=True, track_running_stats=True)(2): ReLU(inplace=True)))(fire4): Fire((squeeze): Sequential((0): Conv2d(16, 8, kernel_size=(1, 1), stride=(1, 1))(1): BatchNorm2d(8, eps=1e-05, momentum=0.1, affine=True, track_running_stats=True)(2): ReLU(inplace=True))(expand_1x1): Sequential((0): Conv2d(8, 8, kernel_size=(1, 1), stride=(1, 1))(1): BatchNorm2d(8, eps=1e-05, momentum=0.1, affine=True, track_running_stats=True)(2): ReLU(inplace=True))(expand_3x3): Sequential((0): Conv2d(8, 8, kernel_size=(3, 3), stride=(1, 1), padding=(1, 1))(1): BatchNorm2d(8, eps=1e-05, momentum=0.1, affine=True, track_running_stats=True)(2): ReLU(inplace=True)))(conv10): Conv2d(16, 2, kernel_size=(1, 1), stride=(1, 1))(avg): AdaptiveAvgPool2d(output_size=1)(maxpool): MaxPool2d(kernel_size=2, stride=2, padding=0, dilation=1, ceil_mode=False)
)print（model）时会显示模型每个层的名字。这里我想对conv10层进行微调，因为它是最后一个具有参数可以微调的层了。当然，如果最后一层是全连接的话，也建议微调最后全连接层。
2、冻结不想训练的层。
这里就有两种不同的方法了：一是新建一个conv10层，替换掉原来的层。二是不新建，直接微调原来的层。
新建：
model.conv10 = nn.Conv2d(model.conv10.in_channels, model.conv10.out_channels, model.conv10.kernel_size, model.conv10.stride)
print(model)可以直接用model.conv10.in_channels等加载原来层的各种参数。这样就定义好了一个新的conv10层，并且已经替换进了模型中。
然后先冻结所有层（requires_grad = False），再放开conv10层（requires_grad = True）。
# 先冻结所有层
for param in model.parameters():param.requires_grad = False# 仅对conv10层进行微调,如果在冻结后新定义了conv10层，这两行可以不写，默认有梯度
for param in model.conv10.parameters():param.requires_grad = True如果不新建层，则不需要运行model.conv10 = nn.Conv2d那一行即可。直接开始冻结就可以。
3、训练
这里一定要注意，optimizer里要设置参数 model.conv10.parameters()，而不是model.parameters()。这是让模型知道它将要训练哪些参数。
optimizer = optim.SGD(model.conv10.parameters(), lr=1e-2)虽然上面已经冻结了不想训练的参数，但是这里最好还是写上model.conv10.parameters()。大家也可以试试不写行不行。
# 使用交叉熵损失函数
criterion = nn.CrossEntropyLoss()
# 只优化conv10层的参数
optimizer = optim.SGD(model.conv10.parameters(), lr=1e-2)
# 将模型移到GPU（如果可用）
device = torch.device("cuda" if torch.cuda.is_available() else "cpu")
model.to(device)# 设置模型为训练模式
model.train()num_epochs = 10
for epoch in range(num_epochs):# model.train()running_loss = 0.0correct = 0for x_train, y_train in data_loader:x_train, y_train = x_train.to(device), y_train.to(device)print(x_train.shape, y_train.shape)# 前向传播outputs = model(x_train)loss = criterion(outputs, y_train)# 反向传播和优化optimizer.zero_grad()loss.backward()optimizer.step()running_loss += loss.item() * x_train.size(0)# 统计训练集的准确率_, predicted = torch.max(outputs, 1)correct += (predicted == y_train).sum().item()# 计算每个 epoch 的训练损失和准确率epoch_loss = running_loss / len(dataset)epoch_accuracy = 100 * correct / len(dataset)# if epoch % 5 == 0 or epoch == num_epochs-1 :print(f'Epoch [{epoch+1}/{num_epochs}]')print(f'Train Loss: {epoch_loss:.4f}, Train Accuracy: {epoch_accuracy:.2f}%')输出显示Loss下降说明模型有在学习。 模型准确率从0变成100，还是非常有成就感的！当然我这里就用了一个样本来微调hhhh。
Epoch [1/10]
Train Loss: 0.8185, Train Accuracy: 0.00%
torch.Size([1, 1, 32, 16]) torch.Size([1])
Epoch [2/10]
Train Loss: 0.7063, Train Accuracy: 0.00%
torch.Size([1, 1, 32, 16]) torch.Size([1])
Epoch [3/10]
Train Loss: 0.6141, Train Accuracy: 100.00%
torch.Size([1, 1, 32, 16]) torch.Size([1])
Epoch [4/10]
Train Loss: 0.5385, Train Accuracy: 100.00%
torch.Size([1, 1, 32, 16]) torch.Size([1])
Epoch [5/10]
Train Loss: 0.4761, Train Accuracy: 100.00%
torch.Size([1, 1, 32, 16]) torch.Size([1])
Epoch [6/10]
Train Loss: 0.4244, Train Accuracy: 100.00%
torch.Size([1, 1, 32, 16]) torch.Size([1])
Epoch [7/10]
Train Loss: 0.3812, Train Accuracy: 100.00%
torch.Size([1, 1, 32, 16]) torch.Size([1])
Epoch [8/10]
Train Loss: 0.3449, Train Accuracy: 100.00%
torch.Size([1, 1, 32, 16]) torch.Size([1])
Epoch [9/10]
Train Loss: 0.3140, Train Accuracy: 100.00%
torch.Size([1, 1, 32, 16]) torch.Size([1])
Epoch [10/10]
Train Loss: 0.2876, Train Accuracy: 100.00%4、验证一下确实是只有这个层参数变化了，而其他层参数没变。
在训练模型之前，看一下这个层的参数：
raw_parm = model.conv10.weight
print(raw_parm)
# 部分输出为
Parameter containing:
tensor([[[[-0.1621]],[[ 0.0288]],[[ 0.1275]],[[ 0.1584]],[[ 0.0248]],[[-0.2013]],[[-0.2086]],[[ 0.1460]],[[ 0.0566]],[[ 0.2897]],[[ 0.2898]],[[ 0.0610]],[[ 0.2172]],[[ 0.0860]],[[ 0.2730]],[[-0.1053]]],训练后，也输出一下这个层的参数：
## 查看微调后模型的参数
tuned_parm = model.conv10.weight
print(tuned_parm)
# 部分输出为：
Parameter containing:
tensor([[[[-0.1446]],[[ 0.0365]],[[ 0.1490]],[[ 0.1783]],[[ 0.0424]],[[-0.1826]],[[-0.1903]],[[ 0.1636]],[[ 0.0755]],[[ 0.3092]],[[ 0.3093]],[[ 0.0833]],[[ 0.2405]],[[ 0.1049]],[[ 0.2925]],[[-0.0866]]],可见这个层的参数确实是变了。
然后检查一下别的随便一个层：
训练前：
# 训练前
raw_parm = model.stem[0].weight
print(raw_parm)
# 部分输出为：
Parameter containing:
tensor([[[[-0.0723, -0.2151, 0.1123],[-0.2114, 0.0173, -0.1322],[-0.0819, 0.0748, -0.2790]]],[[[-0.0918, -0.2783, -0.3193],[ 0.0359, 0.2993, -0.3422],[ 0.1979, 0.2499, -0.0528]]],
训练后：
## 查看微调后模型的参数
tuned_parm = model.stem[0].weight
print(tuned_parm)
# 部分输出为：
Parameter containing:
tensor([[[[-0.0723, -0.2151, 0.1123],[-0.2114, 0.0173, -0.1322],[-0.0819, 0.0748, -0.2790]]],[[[-0.0918, -0.2783, -0.3193],[ 0.0359, 0.2993, -0.3422],[ 0.1979, 0.2499, -0.0528]]],可见参数没有变化。说明这层没有进行学习。
5、为了让大家更容易全面理解，完整代码如下。
import torch
import numpy as np
import torch.optim as optim
import torch.nn as nn
from torchinfo import summary
from torch.utils.data import DataLoader, Dataset,TensorDataset
from sklearn.metrics import confusion_matrix, ConfusionMatrixDisplay, precision_score, recall_score, f1_score
import matplotlib.pyplot as plt
from imblearn.under_sampling import RandomUnderSampler # 多数样本下采样device = torch.device("cuda" if torch.cuda.is_available() else "cpu")## 加载微调数据
feats = np.load("feats_jn105.npy")
labels = np.array([0])
print(feats.shape)
print(labels.shape)# 将data和labels转换为 PyTorch 张量
data_tensor = torch.tensor(feats, dtype = torch.float32, requires_grad=True)
labels_tensor = torch.tensor(labels, dtype = torch.long)# 添加通道维度
# data_tensor = data_tensor.unsqueeze(1) # 变为(num, 1, 32, 16)
batch_size = 15# 创建 TensorDataset
dataset = TensorDataset(data_tensor, labels_tensor)
data_loader = DataLoader(dataset, batch_size = batch_size, shuffle = False)
input, label = next(iter(data_loader))
print(input.shape,label.shape)
# upyter nbconvert --to script ./Model/main_SqueezeNet.ipynb # 终端运行，ipynb转py## 加载要微调的模型
# 环境里必须有模型的框架，才能torch.load
from Model.main_SqueezeNet import SqueezeNet,Firemodel = torch.load("Model/SqueezeNet.pth").to(device)
print(model)# 为模型写一个新的层
# model.fc = nn.Linear(in_features = model.fc.in_features, out_features = model.fc.out_features)
model.conv10 = nn.Conv2d(model.conv10.in_channels, model.conv10.out_channels, model.conv10.kernel_size, model.conv10.stride)
print(model)# 先冻结所有层
for param in model.parameters():param.requires_grad = False# 仅对conv10层进行微调,如果在冻结后新定义了conv10层，这两行可以不写，默认有梯度
for param in model.conv10.parameters():param.requires_grad = Trueraw_parm = model.stem[0].weight
print(raw_parm)
for name, param in model.named_parameters():print(name, param.requires_grad)# 使用交叉熵损失函数
criterion = nn.CrossEntropyLoss()# 只优化c10层的参数
optimizer = optim.SGD(model.conv10.parameters(), lr=1e-2)# 将模型移到GPU（如果可用）
device = torch.device("cuda" if torch.cuda.is_available() else "cpu")
model.to(device)# 设置模型为训练模式
model.train()num_epochs = 10
for epoch in range(num_epochs):# model.train()running_loss = 0.0correct = 0for x_train, y_train in data_loader:x_train, y_train = x_train.to(device), y_train.to(device)print(x_train.shape, y_train.shape)# 前向传播outputs = model(x_train)loss = criterion(outputs, y_train)# 反向传播和优化optimizer.zero_grad()loss.backward()optimizer.step()running_loss += loss.item() * x_train.size(0)# 统计训练集的准确率_, predicted = torch.max(outputs, 1)correct += (predicted == y_train).sum().item()# 计算每个 epoch 的训练损失和准确率epoch_loss = running_loss / len(dataset)epoch_accuracy = 100 * correct / len(dataset)# if epoch % 5 == 0 or epoch == num_epochs-1 :print(f'Epoch [{epoch+1}/{num_epochs}]')print(f'Train Loss: {epoch_loss:.4f}, Train Accuracy: {epoch_accuracy:.2f}%')## 查看微调后模型的参数
tuned_parm = model.stem[0].weight
print(tuned_parm)如有更好的方法，欢迎大家分享~