def jenkins_rao(target, throat_perimeter='throat.perimeter', throat_area=
    'throat.area', throat_diameter='throat.indiameter'):
    """
    Jenkins and Rao relate the capillary pressure in an eliptical throat to
    the aspect ratio

    Parameters
    ----------
    target : OpenPNM Object
        The object which this model is associated with. This controls the
        length of the calculated array, and also provides access to other
        necessary properties.

    throat_perimeter : string
        The dictionary key of the array containing the throat perimeter values.

    throat_area : string
        The dictionary key of the array containing the throat area values.

    throat_diameter : string
        The dictionary key of the array containing the throat diameter values.

    Returns
    -------
    value : NumPy ndarray
        Array containing throat capillary pressure values.

    References
    ----------
    Jenkins, R.G. and Rao, M.B., The effect of elliptical pores on
    mercury porosimetry results. Powder technology, 38(2), pp.177-180. (1984)

    """
    P = target[throat_perimeter]
    A = target[throat_area]
    r = target[throat_diameter] / 2
    value = P / A / (2 / r)
    return value
