Derivative of density wrt. specific enthalpy at constant pressure in steam region for given pressure and specific enthalpy
function dd2hp_Ph input Units.SI.AbsolutePressure p "Pressure"; input Units.SI.SpecificEnthalpy h "Specific enthalpy"; output Units.SI.DerDensityByEnthalpy ddhp "Derivative of density wrt. specific enthalpy at constant pressure"; end dd2hp_Ph;