Fast sigmoid algorithm

Question

The sigmoid function is defined as

I found that using the C built-in function exp() to calculate the value of f(x) is slow. Is th

Answer 1

You can use a simple but effective method by using two formulas:

if x < 0 then f(x) = 1 / (0.5/(1+(x^2)))
if x > 0 then f(x) = 1 / (-0.5/(1+(x^2)))+1

This will look like this:

Two graphs for a sigmoid {Blue: (0.5/(1+(x^2))), Yellow: (-0.5/(1+(x^2)))+1}