--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/extra/nurbs/inst/nrbpermute.m	Wed Mar 27 17:28:48 2013 +0000
@@ -0,0 +1,57 @@
+function tvol = nrbpermute (vol, ord)
+% 
+% NRBPERMUTE: Rearrange the directions of a NURBS volume or surface.
+% 
+% Calling Sequence:
+% 
+%   tvol = nrbpermute(vol,order)
+%
+% INPUT:
+% 
+%   vol		: NURBS volume or surface, see nrbmak.
+%   order   : the order to rearrange the directions of the NURBS entity.
+%
+% OUTPUT:
+% 
+%   tvol	: NURBS volume or surface with rearranged directions.
+% 
+% Description:
+% 
+%   Utility function that rearranges the directions of a NURBS volume or
+%   surface. For surfaces, nrbpermute(srf,[1 2]) is the same as
+%   nrbtransp(srf). NURBS curves cannot be rearranged.
+%
+% Example:
+%
+%    nrbpermute (vol, [1 3 2])
+%
+%    Copyright (C) 2013 Rafael Vazquez
+%
+%    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 2 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/>.
+
+if (~iscell(vol.knots))
+  error('A NURBS curve cannot be rearranged.');
+end
+
+tvol = nrbmak (permute (vol.coefs, [1, ord+1]), {vol.knots{ord}});
+
+%!demo
+%! vol = nrbrevolve (nrb4surf ([1 0], [2 0], [1 1], [2 1]), [0 0 0], [0 1 0], pi/8);
+%! nrbplot(vol,[5 10 20]);
+%! title('NURBS volume and the same after reordering the directions')
+%! hold on
+%! vol.coefs(1,:,:) = vol.coefs(1,:,:) + 2;
+%! vol = nrbpermute(vol,[2 3 1]);
+%! nrbplot(vol,[5 10 20]);
+%! hold off
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