Function kaiser_window 

pub fn kaiser_window(
    n: usize,
    beta: &ExactNum,
    p: usize,
    rm: RoundingMode,
    cc: &mut Consts,
) -> Option<ExactNumArray>

Kaiser–Bessel: I_0(β √(1−t_k²)) / I_0(β) with t_k = (k−(n−1)/2)/((n−1)/2).

beta = 0 is the rectangular window. beta < 0 or non-finite is None.