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## Copyright (C) 2001 Kai Habel
##
## 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.
##
## This program is distributed in the hope that it will be useful, but WITHOUT
## ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
## FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more
## details.
##
## You should have received a copy of the GNU General Public License along with
## this program; if not, see <http://www.gnu.org/licenses/>.
## -*- texinfo -*-
## @deftypefn {Function File} { } fnder (@var{pp}, @var{order})
## differentiate the spline in pp-form
##
## @seealso{ppval}
## @end deftypefn
## Author: Kai Habel <kai.habel@gmx.de>
## Date: 20. feb 2001
function dpp = fnder (pp, o)
if (nargin < 1 || nargin > 2)
print_usage;
endif
if (nargin < 2)
o = 1;
endif
[X, P, N, K, D] = unmkpp (pp);
c = columns (P);
r = rows (P);
for i = 1:o
#pp.P = polyder (pp.P); matrix capable polyder is needed.
P = P(:, 1:c - 1) .* kron ((c - 1):- 1:1, ones (r,1));
endfor
dpp = mkpp (X, P);
endfunction
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