This function returns y = acos(u), with -1 ≤ u ≤ +1, where y is an angle.
function acos extends Modelica.Math.Icons.AxisCenter; input Real u annotation( Dialog(__Dymola_label = "<html><i>u</i></html>")); output Q.Angle y annotation( Dialog(__Dymola_label = "<html><i>y</i></html>")); end acos;