BASISFUNDER:  B-Spline Basis function derivatives

 Calling Sequence:

   ders = basisfunder (ii, pl, uu, k, nd)

    INPUT:

      ii  - knot span
      pl  - degree of curve
      uu  - parametric points
      k   - knot vector
      nd  - number of derivatives to compute

    OUTPUT:

      ders - ders(n, i, :) (i-1)-th derivative at n-th point

   Adapted from Algorithm A2.3 from 'The NURBS BOOK' pg72. 

Package: nurbs