def incid_ref_press(p_d, gamma_inc) ->'p_inc':
    """Calculate DNVGL-ST-F101 «incidental reference pressure». 

    :param p_d: design pressure :math:`(p_d)`
    :type p_d: float
    :param gamma_inc: incidental to design pressure ratio :math:`(\\gamma_{inc})`
    :type gamma_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 page:67 :math:`(p_{inc})`

    .. doctest:: 

        >>> incid_ref_press(100e5, 1.1)
        11000000.0
    """
    return p_d * gamma_inc
