Function simpson 

pub fn simpson(f: impl Fn(f64) -> f64, a: f64, b: f64, n: usize) -> f64

Composite Simpson’s rule $\int_{a}^{b} f(t), dt$ on n intervals (n even, at least 2), exact for cubics.

Examples

use comnum_math::simpson;
assert!((simpson(|t| t * t * t, 0.0, 2.0, 2) - 4.0).abs() < 1e-15);
assert!((simpson(f64::sin, 0.0, std::f64::consts::PI, 200) - 2.0).abs() < 1e-8);