def metalicity_smolec(period, phi31_i):
    """
    Returns the Smolec formula metalicity of the given RRab RR Lyrae.

    (Smolec, 2005) (2)
    (Skowron et al., 2016) (3)

    Parameters
    ----------
    period : float64
        The period of the star.
    phi31_i : float64
        The I band phi31 of the star.

    Returns
    -------
    metalicity_smol : float64
        The Smolec formula metalicity of the star.
    """
    return -3.142 - 4.902 * period + 0.824 * phi31_i