## Copyright (C) 2010-2016   Lukas F. Reichlin
##
## 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 -*-
## Unary minus of a quaternion.  Used by Octave for "-q".

## Author: Lukas Reichlin <lukas.reichlin@gmail.com>
## Created: May 2010
## Version: 0.2

function a = uminus (a)

  if (nargin != 1)
    error ("quaternion: uminus: this is an unary operator");
  endif

  a.w = -a.w;
  a.x = -a.x;
  a.y = -a.y;
  a.z = -a.z;

endfunction


%!test
%! q = quaternion (1, 2, 3, 4);
%! result = -q;
%! expected = quaternion (-1, -2, -3, -4);
%! assert (result == expected);
