Function interval_bisection 

pub fn interval_bisection<F>(
    f_interval: F,
    initial: Interval,
    tol: f64,
    max_depth: usize,
) -> Vec<Interval>
where
    F: Fn(Interval) -> Interval,

Find all root-containing sub-intervals using bisection with an inclusion function.

Subdivides initial into pieces of width ≤ tol, keeping only those sub-intervals where f_interval contains zero.