def reip(b4, b5, b6, b7):
    """
    Red-edge Inflection Point (Herrmann et al. 2011).

    .. math:: REIP = 700 + 40 * ((((b4 + b7) / 2) - b5) / (b6 - b5))

    :param b4: Red.
    :type b4: numpy.ndarray or float
    :param b5: Red-edge 1.
    :type b5: numpy.ndarray or float
    :param b6: Red-edge 2.
    :type b6: numpy.ndarray or float
    :param b7: Red-edge 3.
    :type b7: numpy.ndarray or float

    :returns REIP: Index value

    .. Tip::

       Herrmann, I., Pimstein, A., Karnieli, A., Cohen, Y., Alchanatis, V., \
       Bonfil, D. J. 2011. LAI assessment of wheat and potato crops by VENμS \
       and Sentinel-2 bands. Remote Sensing of Environment 115, 2141-2151. \
       doi:10.1016/j.rse.2011.04.018.
    """

    REIP = 700 + 40 * ((((b4 + b7) / 2) - b5) / (b6 - b5))
    return REIP