Function brent 

pub fn brent(
    f: impl Fn(f64) -> f64,
    a: f64,
    b: f64,
    c: f64,
    tol: f64,
) -> (f64, f64)

Brent’s method for 1-D minimization given a bracketing triple (a, b, c) where b is between a and c and f(b) < f(a), f(b) < f(c).

Returns (x_min, f_min).