derivative function of rho_pT
function rho_pT_der extends Modelica.Icons.Function; input Units.SI.Pressure p "pressure"; input Units.SI.Temperature T "temperature"; input ThermoSysPro.Properties.WaterSteam.Common.IF97TwoPhaseAnalytic aux "auxiliary record"; input Real p_der "derivative of pressure"; input Real T_der "derivative of temperature"; output Real rho_der "derivative of density"; end rho_pT_der;