Returns e^x - 1. Near 0, expm1(x)+1 is more accurate to e^x than exp(x). If x is ##NaN => ##NaN If x is ##Inf => #Inf If x is ##-Inf => -1.0 If x is zero => x See: https://docs.oracle.com/javase/8/docs/api/java/lang/Math.html#expm1-double-