Quat2anax.m

Converts a quaternion into angle-axis rotation parameters. Syntax:

                [rot_axis,rot_angle]=quat2anax(q)

where q is a structure with four fields q.u, q.i, q.j, q.k giving the four components of the quaternion. Output:

   rot_axis - cartesian direction vector given as a row or column 
              with three real elements

  rot_angle - rotation angle in radians