--- /dev/null
+## Copyright (C) 2010, 2011 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 -*-
+## @deftypefn {Function File} {@var{qabs} =} abs (@var{q})
+## Modulus of a quaternion.
+##
+## @example
+## q = w + x*i + y*j + z*k
+## abs (q) = sqrt (w.^2 + x.^2 + y.^2 + z.^2)
+## @end example
+## @end deftypefn
+
+## Author: Lukas Reichlin <lukas.reichlin@gmail.com>
+## Created: August 2010
+## Version: 0.2
+
+function b = abs (a)
+
+ if (nargin != 1)
+ print_usage ();
+ endif
+
+ b = sqrt (norm2 (a));
+
+endfunction