Add a useful package (from Source forge) for octave

[CreaPhase.git] / octave_packages / quaternion-2.0.0 / @quaternion / diff.m

diff --git a/octave_packages/quaternion-2.0.0/@quaternion/diff.m b/octave_packages/quaternion-2.0.0/@quaternion/diff.m
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+## Copyright (c) 1998, 2000, 2005, 2007 Auburn University.
+## Copyright (c) 2011 Juan Pablo Carbajal <carbajal@ifi.uzh.ch>
+##
+## 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{qdot} =} diff (@var{q}, @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' = diff(Q, omega)
+## @end example
+##
+## If the passive convention is used (rotate the frame, not the vector),
+## then
+##
+## @example
+## Q' = diff(Q,-omega)
+## @end example
+## @end deftypefn
+
+## Adapted from: qderiv by A. S. Hodel <a.s.hodel@eng.auburn.edu>
+
+function qd = diff (q, Omega)
+
+  if (nargin != 2)
+    print_usage ();
+  endif
+
+  if (! isa (q, "quaternion") || ! isscalar (q.w))
+    error ("quaternion: first argument '%s' must be a scalar quaternion", inputname(1));
+  endif
+
+  Omega = vec (Omega);
+
+  if (length (Omega) != 3)
+    error ("quaternion: second argument '%s' must be a length 3 vector", inputname(2));
+  endif
+
+  qd = 0.5 * quaternion (Omega(1), Omega(2), Omega(3)) * q;
+
+endfunction
+
+%!shared q
+%! q = quaternion(3,1,0,0);
+
+%!assert(quaternion(0,0,0.5,1.5) == diff(q,[0 0 1]))
+%!assert(quaternion(0,0,2,1) == diff(q,[0 1 1]))