This class is used to draw function lines y = f(x) in a 2D scatter chart
You may call newFunctionLine(...) of IDataLineSet interface to get a new object
Note: (1) This class is only useful for 2D scatter charts.
(2) The function cannot be saved to or read from a cht/tpl file
(3) No line style supported
For instance,
QbChart chart = new QbChart(...);
IFunctionLine line = chart.gethDataLineSet().newFunctionLine(...);