def F_to_M(F, ecc):
    r"""Mean anomaly from eccentric anomaly.

    Parameters
    ----------
    F : float
        Hyperbolic anomaly.
    ecc : float
        Eccentricity (>1).

    Returns
    -------
    M : float
        Mean anomaly.

    Notes
    -----
    As noted in [5]_, by manipulating
    the parametric equations of the hyperbola
    we can derive a quantity that is equivalent
    to the eccentric anomaly in the elliptic case:

    .. math::

        M = e \sinh{F} - F

    """
    M = ecc * np.sinh(F) - F
    return M