temperature as function of pressure and specific entropy
function T_ps extends Modelica.Icons.Function; input SI.Pressure p "pressure"; input 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 SI.Temperature T "Temperature"; end T_ps;