function velocityOfSound_duX input Modelica.SIunits.Density d "Density"; input Modelica.SIunits.SpecificInternalEnergy u "Specific internal energy"; input Modelica.SIunits.MassFraction X[nC] = reference_X "Mass fraction"; input Properties state; input MultiPhaseMixture.Templates.ExternalObjects.ExternalMediaObject eo "External object"; output Real a; end velocityOfSound_duX;