def incidental_reference_pressure(p_d, γ_inc):
    """Calculate DNVGL-ST-F101 «incidental reference pressure». 

    :param p_d: design pressure :math:`(p_d)`
    :type p_d: float
    :param γ_inc: incidental to design pressure ratio :math:`(\gamma_{inc})`
    :type γ_inc: float
    :returns: p_inc incidental reference pressure :math:`(p_{inc})`
    :rtype: float

    Reference:
    DNVGL-ST-F101 (2017-12) 
        eq:4.3 sec:4.2.2.2 p:67 :math:`(p_{inc})`

    .. doctest:: 

        >>> incid_ref_press(100e5, 1.1)
        11000000.0
    """
    p_inc = p_d * γ_inc
    return p_inc