This function adds the ideal gas contribution of the fundamental
equation to the residual contribution and computes the helmholtz
derivatives w.r.t. temperature and density.
function f_R134a
extends Modelica.Icons.Function;
input Density d "Density";
input Temperature T "Temperature";
output Modelica.Media.Common.HelmholtzDerivs f "Helmholtz derivatives";
end f_R134a;