Function chebyshev_coeffs 

pub fn chebyshev_coeffs<F>(
    f: F,
    n: usize,
    a: &ExactNum,
    b: &ExactNum,
    p: usize,
    rm: RoundingMode,
    cc: &mut Consts,
) -> Option<Vec<ExactNum>>
where
    F: FnMut(&ExactNum, usize, RoundingMode, &mut Consts) -> ExactNum,

Interpolation coefficients of f on [a, b] at the n Chebyshev–Gauss nodes.

c_0 = (1/n) Σ f(x_k), c_j = (2/n) Σ f(x_k) T_j(t_k) for j ≥ 1, so f(x) ≈ Σ_{j=0}^{n-1} c_j T_j(t(x)) with t the affine map to [-1, 1].

None if n is 0 or greater than CHEBYSHEV_MAX_DEGREE, or if the interval is not a finite a < b.