Return specific volume derivative with respect to individual mass fraction
function v_pTX_derX input Modelica.SIunits.AbsolutePressure p "Pressure"; input Modelica.SIunits.Temperature T "Temperature"; input Modelica.SIunits.MassFraction[nS] X "Mass fraction"; output Modelica.SIunits.SpecificVolume[nS] v_derX "Specific volume derivative"; end v_pTX_derX;