代码中AFF模块中，为什么要用2×呢？

[YoungLNB]

xo = 2 * x * wei + 2 * residual * (1 - wei)

[Sunkey2333]

作者之前在其他 issue 回答过：

I believe it has no impact on the training. The reason I use the multiplication of 2 is that I want to keep the total weights the same as addition.

In the direct addition case, X + Y is actually 1 * X + 1 * Y, the sum of the weight is 2. However, in a soft selection way, M(X+Y) * X + (1 - M(X+Y)) * Y, the sum of the weight is 1, so I multiply 2 to keep them the same. Then the only difference between 1 * X + 1 * Y and 2 * M(X+Y) * X + 2 * (1 - M(X+Y)) * Y is the dynamic weight allocation, but the sum of the weights keeps the same.