Function spherical_harmonic 

pub fn spherical_harmonic(
    l: usize,
    m: isize,
    costheta: f64,
    phi: f64,
) -> Complex64

Computes the spherical harmonic $Y_{\ell}^m(\theta, \phi)$ (given $\cos\theta$). Note that this formulation includes the Condon-Shortley phase.