## Copyright (C) 1995-2012 Kurt Hornik
##
## This file is part of Octave.
##
## Octave 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.
##
## Octave 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 Octave; see the file COPYING.  If not, see
## <http://www.gnu.org/licenses/>.

## -*- texinfo -*-
## @deftypefn  {Function File} {} fastcross (@var{x}, @var{y})
## @deftypefnx {Function File} {} cross (@var{x}, @var{y}, @var{dim})
## Fast compute the vector cross product of two 3-vectors ONLY
## @var{x} : size 1 x 3 and @var{y} : size 1 x 3
##
## @example
## @group
## fastcross ([1,1,0], [0,1,1])
##      @result{} [ 1; -1; 1 ]
## @end group
## @end example
##
## Simplified cross product assuming @var{x} and @var{y} are 3-vectors, 
## the cross product is applied along the 3-vectors as given.   
## @seealso{dot, curl, divergence}
## @end deftypefn

## Author: Kurt Hornik <address@hidden>
## Created: 15 October 1994
## Adapted-By: jwe
## Modified by DRE 2013 <address@hidden>
function z = fastcross (x, y)
%% ONE safety
if (find (size (x) == 3, 1)== 2 && find (size (y) == 3, 1))
%% ONE STEP cross product 
	z = cat (2, (x(1,2)*y(1,3) - x(1,3)*y(1,2)), (x(1,3)*y(1,1) - x(1,1)*y(1,3)), \
		 (x(1,1)*y(1,2) - x(1,2)*y(1,1)));
else
       error ("fastcross: x and y must have 1 x 3 elements");
endif
endfunction