def nbr2(b11, b12):
    """
    Normalized Burn Ratio-2 (García and Caselles, 1991).

    .. math:: NBR2 = (b11 - b12) / (b11 + b12)

    :param b11: SWIR 1.
    :type b11: numpy.ndarray or float
    :param b12: SWIR 2.
    :type b12: numpy.ndarray or float

    :returns NBR2: Index value

    .. Tip::

        García, M. J. L., Caselles, V. 1991. Mapping burns and natural \
        reforestation using thematic Mapper data. Geocarto International \
        6(1), 31-37. doi:10.1080/10106049109354290.
    """

    NBR2 = (b11 - b12) / (b11 + b12)
    return NBR2