pytorch自定义loss损失函数
目录
- 步骤1:添加自定义的类
- 步骤2:修改使用的loss函数
自定义loss
的方法有很多,但是在博主查资料的时候发现有挺多写法会有问题,靠谱一点的方法是把loss作为一个pytorch的模块,
比如:
class CustomLoss(nn.Module): # 注意继承 nn.Module def __init__(self): super(CustomLoss, self).__init__() def forward(self, x, y): # .....这里写x与y的处理逻辑,即loss的计算方法 return loss # 注意最后只能返回Tensor值,且带梯度,即 loss.requires_grad == True
示例代码:
以一个pytorch求解线性回归的代码为例:
import torch import torch.nn as nn import numpy as np import os os.environ["KMP_DUPLICATE_LIB_OK"] = "TRUE" def get_x_y(): np.random.seed(0) x = np.random.randint(0, 50, 300) y_values = 2 * x + 21 x = np.array(x, dtype=np.float32) y = np.array(y_values, dtype=np.float32) x = x.reshape(-1, 1) y = y.reshape(-1, 1) return x, y class LinearRegressionModel(nn.Module): def __init__(self, input_dim, output_dim): super(LinearRegressionModel, self).__init__() self.linear = nn.Linear(input_dim, output_dim) # 输入的个数,输出的个数 def forward(self, x): out = self.linear(x) return out if __name__ == '__main__': input_dim = 1 output_dim = 1 x_train, y_train = get_x_y() model = LinearRegressionModel(input_dim, output_dim) epochs = 1000 # 迭代次数 optimizer = torch.optim.SGD(model.parameters(), lr=0.001) model_loss = nn.MSELoss() # 使用MSE作为loss # 开始训练模型 for epoch in range(epochs): epoch += 1 # 注意转行成tensor inputs = torch.from_numpy(x_train) labels = torch.from_numpy(y_train) # 梯度要清零每一次迭代 optimizer.zero_grad() # 前向传播 outputs: torch.Tensor = model(inputs) # 计算损失 loss = model_loss(outputs, labels) # 返向传播 loss.backward() # 更新权重参数 optimizer.step() if epoch % 50 == 0: print('epoch {}, loss {}'.format(epoch, loss.item()))
步骤1:添加自定义的类
我们就用自定义的写法来写与MSE相同的效果,MSE计算公式如下:
添加一个类:
class CustomLoss(nn.Module): def __init__(self): super(CustomLoss, self).__init__() self.mse_loss = nn.MSELoss() def forward(self, x, y): mse_loss = torch.mean(torch.pow((x - y), 2)) # x与y相减后平方,求均值即为MSE return mse_loss
步骤2:修改使用的loss函数
只需要把原始代码中的:
model_loss = nn.MSELoss() # 使用MSE作为loss
改为:
model_loss = CustomLoss() # 自定义loss
即可
完整代码:
import torch import torch.nn as nn import numpy as np import os os.environ["KMP_DUPLICATE_LIB_OK"] = "TRUE" def get_x_y(): np.random.seed(0) x = np.random.randint(0, 50, 300) y_values = 2 * x + 21 x = np.array(x, dtype=np.float32) y = np.array(y_values, dtype=np.float32) x = x.reshape(-1, 1) y = y.reshape(-1, 1) return x, y class LinearRegressionModel(nn.Module): def __init__(self, input_dim, output_dim): super(LinearRegressionModel, self).__init__() self.linear = nn.Linear(input_dim, output_dim) # 输入的个数,输出的个数 def forward(self, x): out = self.linear(x) return out class CustomLoss(nn.Module): def __init__(self): super(CustomLoss, self).__init__() self.mse_loss = nn.MSELoss() def forward(self, x, y): mse_loss = torch.mean(torch.pow((x - y), 2)) return mse_loss if __name__ == '__main__': input_dim = 1 output_dim = 1 x_train, y_train = get_x_y() model = LinearRegressionModel(input_dim, output_dim) epochs = 1000 # 迭代次数 optimizer = torch.optim.SGD(model.parameters(), lr=0.001) # model_loss = nn.MSELoss() # 使用MSE作为loss model_loss = CustomLoss() # 自定义loss # 开始训练模型 for epoch in range(epochs): epoch += 1 # 注意转行成tensor inputs = torch.from_numpy(x_train) labels = torch.from_numpy(y_train) # 梯度要清零每一次迭代 optimizer.zero_grad() # 前向传播 outputs: torch.Tensor = model(inputs) # 计算损失 loss = model_loss(outputs, labels) # 返向传播 loss.backward() # 更新权重参数 optimizer.step() if epoch % 50 == 0: print('epoch {}, loss {}'.format(epoch, loss.item()))
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