def METHOD_NAME(rotor):
    """Compute rotation matrix from rotor.
    Parameters
    ----------
    rotor : array-like, shape (4,)
        Rotor: (a, b_yz, b_zx, b_xy)
    Returns
    -------
    R : array, shape (3, 3)
        Rotation matrix
    """
    rotor = check_rotor(rotor)
    return np.column_stack((
        rotor_apply(rotor, unitx), rotor_apply(rotor, unity),
        rotor_apply(rotor, unitz)))