density as function of pressure and specific entropy
function rho_ps extends Modelica.Icons.Function; input Units.SI.Pressure p "pressure"; input Units.SI.SpecificEntropy s "specific entropy"; input Integer phase = 0 "2 for two-phase, 1 for one-phase, 0 if not known"; input Integer region = 0 "if 0, region is unknown, otherwise known and this input"; output Units.SI.Density rho "density"; end rho_ps;