For an ideal gas, this function is independent of temperature (although temperature remains as a valid input).
function beta extends Modelica.Icons.Function; input Q.TemperatureAbsolute T = 298.15*U.K "Temperature" annotation( Dialog(__Dymola_label = "<html><i>T</i></html>")); input Q.PressureAbsolute p = p0 "Pressure" annotation( Dialog(__Dymola_label = "<html><i>p</i></html>")); output Q.PressureReciprocal beta "Isothermal compressibility"; end beta;