Derivative of g w.r.t. pi and tau
function g2pitau extends Modelica.Icons.Function; input SI.Pressure p "Pressure"; input SI.Temperature T "Temperature (K)"; output Real pi "Dimensionless pressure"; output Real tau "Dimensionless temperature"; output Real gpi "Dimensionless derivative of Gibbs function w.r.t. pi"; output Real gtau "Dimensionless derivative of Gibbs function w.r.t. tau"; end g2pitau;