Compute specific volume derivative
function v_pTX_derp input Modelica.SIunits.AbsolutePressure p "Pressure"; input Modelica.SIunits.Temperature T "Temperature"; input Modelica.SIunits.MassFraction[nS] X "Mass fraction"; output Real v_derp(unit = "m3/(kg.Pa)") "Specific volume derivative"; end v_pTX_derp;