compute in a changing group

Dear all:

I want to simulation several atom clusters hitting target by defining a changing group, like this(only the related code):

variable loopd loop 20
label loop
region r1 sphere random(10,-10,100) random(5,-5,3) 7 5
create_atoms 1 region r1
group g1 region r1

compute 1 all ke/atom

run 20
region r1 delete
next loopp
jump SELF loop

the error is : reuse of compute ID

then how to solve this problem?

You can't redefine a compute with an ID that has
already been used. I guess you could put an uncompute
command in your loop, but I'm not sure what you are
trying to do.