def rISCO_14067295(a):
    """
    Calculate the ISCO radius of a Kerr BH as a function of the Kerr parameter using eqns. 2.5 and 2.8 from Ori and Thorne, Phys Rev D 62, 24022 (2000)

    Parameters
    ----------
    a : Kerr parameter

    Returns
    -------
    ISCO radius
    """
    import numpy as np
    a = np.array(a)
    z1 = 1.0 + (1.0 - a ** 2.0) ** (1.0 / 3) * ((1.0 + a) ** (1.0 / 3) + (
        1.0 - a) ** (1.0 / 3))
    z2 = np.sqrt(3 * a ** 2 + z1 ** 2)
    a_sign = np.sign(a)
    return 3 + z2 - np.sqrt((3.0 - z1) * (3.0 + z1 + 2.0 * z2)) * a_sign
