pub(super) fn gamma_derivative(n: f64, z: Complex) -> Complex
The argument derivative dGamma(n, z)/dz = -z^(n-1) e^-z, with its limits -1 (n = 1) and 0 (n > 1) at z = 0.
dGamma(n, z)/dz = -z^(n-1) e^-z
-1
n = 1
0
n > 1
z = 0