Function derivatives 

pub fn derivatives<P: Blend>(
    knots: &KnotVector,
    control: &[P],
    u: f64,
    n: usize,
    tol: Tolerances,
) -> OgeomResult<Vec<P>>

Evaluate a B-spline and its derivatives up to order n.

result[0] is the point; result[k] is the kth derivative. Orders above the degree are zero.

Errors

As evaluate.