## Copyright (C) 1998 Auburn University. All rights reserved.
##
## 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 2, 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, write to the Free
## Software Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
## 02110-1301, USA.
## -*- texinfo -*-
## @deftypefn {Function File} {} qderivmat (@var{omega})
## Derivative of a quaternion.
##
## Let Q be a quaternion to transform a vector from a fixed frame to
## a rotating frame. If the rotating frame is rotating about the
## [x, y, z] axes at angular rates [wx, wy, wz], then the derivative
## of Q is given by
##
## @example
## Q' = qderivmat (omega) * Q
## @end example
##
## If the passive convention is used (rotate the frame, not the vector),
## then
##
## @example
## Q' = -qderivmat (omega) * Q.
## @end example
## @end deftypefn
## Author: A. S. Hodel
## Adapted-By: jwe
function Dmat = qderivmat (Omega)
Omega = vec (Omega);
if (length (Omega) != 3)
error ("qderivmat: Omega must be a length 3 vector");
endif
Dmat = 0.5 * [ 0.0, Omega(3), -Omega(2), Omega(1);
-Omega(3), 0.0, Omega(1), Omega(2);
Omega(2), -Omega(1), 0.0, Omega(3);
-Omega(1), -Omega(2), -Omega(3), 0.0 ];
endfunction