Compute partial derivative of density wrt. mass fraction
function dddX_pTX input Modelica.SIunits.AbsolutePressure p "Pressure"; input Modelica.SIunits.Temperature T "Temperature"; input Modelica.SIunits.MassFraction X[:] "Mass fractions"; output Real[size(X, 1)] dddX(unit = "kg/m3"); end dddX_pTX;