derivative function of ddhp
function ddhp_ph_der extends Modelica.Icons.Function; input Units.SI.Pressure p "pressure"; input Units.SI.SpecificEnthalpy h "specific enthalpy"; input ThermoSysPro.Properties.WaterSteam.Common.IF97TwoPhaseAnalytic aux "auxiliary record"; input Real p_der "derivative of pressure"; input Real h_der "derivative of specific enthalpy"; output Real ddhp_der "Gradient of ddhp"; end ddhp_ph_der;