questions about compute centre/atom command

I have asked this question before,but I have not found the method to tackle it.My question is that I use compute centre/atom command to calculate the value of the centro-symmetry parameter CS and I need to get the surface atoms which their CS=9~20 coz I want to heat the surface atoms.
I have ever used a matlab programme to choose these surface atoms from dump files,however it is too complicated coz i must to halt the in.file every 100 timesteps.Do you have some conveniment method to solve this problem? I really need you help.
appreciate for your help~

You can heat the surface atoms with the fix heat command
if you define a group that has only the surf atoms in it.
The group variable command can be used to put atoms
defined by an atom-style variable in the group. An atom
style variable can have logic that compares a compute
centro/atom to a threshold value of your choosing and
returns a 0 or 1 to choose/unchoose an atom. See the
doc pages for all those commands for details.