def a_from_p(p, m1, m2):
    """Computes the separation from orbital period with KEPLER III

    Parameters
    ----------
    p : float/array
        orbital period [day]
    m1 : float/array
        primary mass [msun]
    m2 : float/array
        secondary mass [msun]

    Returns
    -------
    sep : float/array
        separation [rsun]
    """
    p_yr = p / 365.25
    sep_3 = p_yr ** 2 * (m1 + m2)
    sep = sep_3 ** (1 / 3.0)
    sep_rsun = sep * 215.032
    return sep_rsun
