/| x |\ x - log\|E + 1|/
x - log(|E^x + 1|)
x e 1 - -------- | x | |E + 1|
/ x \ | e | x |-1 + ------|*e | x| \ 1 + e / ---------------- x 1 + e
/ 2*x x \ | 2*e 3*e | x |-1 - --------- + ------|*e | 2 x| | / x\ 1 + e | \ \1 + e / / ---------------------------- x 1 + e