Function multidimensional_trap 

pub fn multidimensional_trap(
    f: impl Fn(&[f64]) -> f64,
    bounds: &[(f64, f64)],
    n: usize,
) -> f64

Approximate ∫ f(x) dx over a hyperrectangle using the composite trapezoid rule.

bounds is a slice of (a_i, b_i) pairs, one per dimension. n is the number of subintervals per dimension.