def rectangle(target, throat_length='throat.length'):
    """
    Calculate surface area for a rectangular throat

    Only suitable for true 2D simulations

    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_length : string
        Dictionary key to the throat length array.  Default is 'throat.length'.

    """
    return 2 * target[throat_length]
