A problem about the command "compute group/group".

Dear Alex:
I just to the extract the constitutive relation of the interface. And now I can know the displacement of the two groups , the other things I need to know is the stress between them.
I do not know how to do this in lammps.
Simen Zhou
School of Aeronautics sicence and engineering
Beihang university
Xueyuan road No 31. Haidian district. Beijing

If you're using a pair potential, you can compute the force between
the 2 groups with compute group/group. If you're using
a manybody potential, you can't. But you could sum the force
on atoms in each group. If they only interact with each other,
than the net force on one group is due to the other.

Steve