As long as it's differentiable, and the derivative isn't too crazy to calculate it's fine. In this case Sigmoid Colon is a third degree polynomial. Computationa

As long as it's differentiable, and the derivative isn't too crazy to calculate it's fine. In this case Sigmoid Colon is a third degree polynomial. Computationally it should be fine, but the cube term probably means that you will have numerical stability issues if your data is not very normalized.