folding surface with attarctor points

Hello guys, I need some help here, Im working with a defition that takes a surfaces and divided it in a grid of points, also these points generate a kind of a folding surface, just I want to get these foldings just in a part or section of the surface and then the folds become vanished.here Ive attached the definition too.

Ive tryed to find the point between the the corner points of the surface but I dont know how to link this point with the surface and the other points