/*
* validate if the function has that point in a sensible area returning the index where the point was found or -1 if is in not part of the function: define the sensible area is
* x1-validPointRange<x<x1+validPointRange y1-validPointRange<y<y1+validPointRange
/*
* validate if the function has that point in a sensible area returning the index where the point was found or -1 if is in not part of the function: define the sensible area is
* x1-validPointRange<x<x1+validPointRange y1-validPointRange<y<y1+validPointRange