pub fn expm1(x: f64) -> f64
Exponential, base e, of x-1 (f64)
Calculates the exponential of
x and subtract 1, that is, e raised
to the power
x minus 1 (where e is the base of the natural
system of logarithms, approximately 2.71828).
The result is accurate even for small values of
exp(x)-1 would lose many significant digits.