1st derivatives of f w.r.t. delta and tau
function f3deltatau extends Modelica.Icons.Function; input SI.Density d "Density"; input SI.Temperature T "Temperature (K)"; output Real delta "Dimensionless density"; output Real tau "Dimensionless temperature"; output Real fdelta "Dimensionless derivative of Helmholtz function w.r.t. delta"; output Real ftau "Dimensionless derivative of Helmholtz function w.r.t. tau"; end f3deltatau;