Function integrate_fixed 

pub fn integrate_fixed<N: ComplexField + FromPrimitive + Copy, F: FnMut(N::RealField) -> N>(
    left: N::RealField,
    right: N::RealField,
    f: F,
    n: usize,
) -> Result<N, String>
where
    <N as ComplexField>::RealField: FromPrimitive + Copy,

Numerically integrate a function over an interval.

Given a function and end points, numerically integrate using Romberg integration. Uses n steps.