Derivative of partial pressure of steam
function pd_pTX_der extends Modelica.Icons.Function; input SI.AbsolutePressure p "Pressure"; input SI.Temperature T "Temperature"; input SI.MassFraction X[:] = Modelica.Media.Air.ReferenceMoistAir.reference_X "Mass fractions"; input Real p_der "Derivative of pressure"; input Real T_der "Derivative of temperature"; input Real X_der[:] "Derivative of mass fractions"; output Real pd_der "Derivative of partial pressure"; end pd_pTX_der;