i used DS2.1 to creat a GFA qsar model ,here's my questions:
a. what's the difference between "R-squared" and"Friedman LOF" in scoring funtion?

b. what's the meaning of "none" in "additional terms"? and what's the difference between all these options such as "none","binary interaction","simple quadratic" etc?


c.is the "Cross validated R−squared" in the report refers to LOO?


thanks