NRBEVAL_DER_P: Compute the derivative of a NURBS object at a given point 
 with respect to the coordinates of the i-th control point.

 Calling Sequence:
 
   der = nrbeval_der_p (crv, i, u);
   der = nrbeval_der_p (srf, i, p);
   der = nrbeval_der_p (srf, i, {u v});
   der = nrbeval_der_p (vol, i, p);
   der = nrbeval_der_p (vol, i, {u v w});

 INPUT:
 
   crv	   - NURBS curve.
   srf	   - NURBS surface.
   vol	   - NURBS volume.
   i      - Index of the control point.
   u or p(1,:,:)  - parametric points along u direction
   v or p(2,:,:)  - parametric points along v direction
   w or p(3,:,:)  - parametric points along w direction

 OUTPUT:

   der - Derivative.
          size(der) = numel(u) for curves
          or          numel(u)*numel(v) for surfaces
          or          numel(u)*numel(v)*numel(w) for volumes
   
 Copyright (C) 2015 Jacopo Corno

    This program is free software: you can redistribute it and/or modify
    it under the terms of the GNU General Public License as published by
    the Free Software Foundation, either version 3 of the License, or
    (at your option) any later version.

Package: nurbs