BatchNormalization在训练过程中既使用批次内的均值和方差,又使用移动平均值和方差。具体步骤如下:
以下是使用PyTorch实现BatchNormalization和移动平均值的示例代码:
import torch
import torch.nn as nn
class Model(nn.Module):
def __init__(self, num_features):
super(Model, self).__init__()
self.bn = nn.BatchNorm1d(num_features)
self.linear = nn.Linear(num_features, 1)
def forward(self, x):
x = self.bn(x)
x = self.linear(x)
return x
# 创建模型实例
model = Model(num_features=10)
# 训练模式
model.train()
# 假设有一个批次的数据,大小为(batch_size, num_features)
batch_size = 32
num_features = 10
x = torch.randn(batch_size, num_features)
# 前向传播
output = model(x)
# 手动更新移动平均值
model.eval() # 切换到推理模式
# 计算移动平均值
running_mean = model.bn.running_mean
running_var = model.bn.running_var
# 更新移动平均值
momentum = 0.1 # 动量因子,用于平滑移动平均值的更新
running_mean = momentum * running_mean + (1 - momentum) * model.bn.running_mean
running_var = momentum * running_var + (1 - momentum) * model.bn.running_var
# 使用移动平均值进行推理
model.bn.running_mean = running_mean
model.bn.running_var = running_var
# 推理模式下的前向传播
output = model(x)
在训练过程中,PyTorch会自动更新BatchNormalization层的running_mean和running_var。在推理阶段,我们可以手动更新这两个值,然后将其赋值给模型的BatchNormalization层,以便使用移动平均值进行归一化。