Thank you very much for your answer. I think I understand what you mean. So at this point, both LL and I at the boundary execute des_usr_var(1, ll) = des_usr_var(1, ll) + 1? And des_usr_var(1, ll) = des_usr_var(1, ll) -1 does not work?
des_usr_var(1, ll) = des_usr_var(1, ll) + 1
des_usr_var(1, i) = des_usr_var(1, i) - 1
Yes, these two lines will be executed.
However, since i is a ghost particle, the operation doesn’t have any real meaning, its value will eventually be replaced by the data received from the rank that actually owns this particle.
Thank you very much for your reply. I am sorry for not replying for so long. I would also like to ask why there is no need to check IF(.NOT.IS_NORMAL(LL)) CYCLE in calc_force_dem.f?
I think mfix does not build neighbor list for ghost particle. Check or not should not make any difference, because mfix does not update velocity and displacement for ghost particles as well.
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Thank you very much! I think I understand now.