Apply jitter (deformation) to surface

trying to add slight deformation (jitter, cloth like, etc) to a surface.
but need the border to stay intact, how would I ignore all the points
along the surface border ? or is there a better way to do this ?
thnx!

very cool! I was trying to use InCurve somehow to make it work.
big thnx!

hallo, question want to use same nodes system but the points to be selectd from a surface , how can i achive that, i want to apply t to any surface

deformationWithFixedEdge.gh (17.9 KB)