Anax2quat.m

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

                 q=anax2quat(rot_axis,rot_angle)

Arguments:

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

    rot_angle - rotation angle in radians

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