def _anisotropy(haeb_evals, reduced=False):
    """Calculate anisotropy given eigenvalues sorted with Haeberlen
    convention"""
    f = 2.0 / 3.0 if reduced else 1.0
    return (haeb_evals[:, (2)] - (haeb_evals[:, (0)] + haeb_evals[:, (1)]) /
        2.0) * f
