Function suq_cos 

pub fn suq_cos(x: f64, k: f64) -> f64

Implements the superquadric auxiliary involving cos(x)

suq_cos(x;k) = sign(cos(x)) · |cos(x)|ᵏ

suq_cos(x;k) is the g(ω;m) function from https://en.wikipedia.org/wiki/Superquadrics