// function sys = dor_awpdtops(wf, ps, pd, cd, sg);
// Differential area/flow/discharge pressure to supply pressure.
// Author:       D. A. Gutz
// Written:      22-Jun-92
// Revisions:    19-Aug-92 Simplify return arguments.
// 
// Input:
// cd    Coefficient of discharge.
// pd    Discharge pressure, psia.
// ps    Supply pressure, psia.
// sg    Specific gravity.
// wf    Flow, pph.
// 
// Differential IO:
// a     Input  # 1, area perturbation, sqin.
// wf    Input  # 2, differential flow, pph.
// pd    Input  # 3, differential discharge pressure, psi.
// ps    Output # 1, differential supply pressure, psi.
// 
// Local:
// ao     Orifice area, sqin.
// dpda   Partial pressure to area, psi/sqin.
// dpdw   Partial pressure to flow, psi/pph.
// 
// States:
// none.
// 
// Functions called:
// or_wptoa Orifice area.
// Copyright (C) 2018 - Dave Gutz
//
// Permission is hereby granted, free of charge, to any person obtaining a copy
// of this software and associated documentation files (the "Software"), to deal
// in the Software without restriction, including without limitation the rights
// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
// copies of the Software, and to permit persons to whom the Software is
// furnished to do so, subject to the following conditions:
//
// The above copyright notice and this permission notice shall be included in all
// copies or substantial portions of the Software.
//
// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
// SOFTWARE.
// Sep 26, 2018 	DA Gutz		Created
// 
//**********************************************************************
function [sys] = lti_dor_awpdtops(wf, ps, pd, %cd, sg)

    // Output variables initialisation (not found in input variables)
    sys=[];

    // Display mode
    mode(0);

    // Display warning for floating point exception
    ieee(1);

    // Parameters.
    ao = or_wptoa(wf, ps, pd, %cd, sg);

    // Partials.
    dpda = -2 * (ps-pd) / ao;
    dpdw = 2 * (ps-pd) / wf;

    // Connections and system construction.
    a = [];
    b = [];
    c = [];
    e = [dpda,dpdw,1];

    // Form the system.
    sys = pack_ss(a, b, c, e);

endfunction
