[gmx-developers] Problem with Run time exceeded

[francesco oteri]

Dear gromacs developers,

analyzing a hunging replica exchange simulation, I might have figured out a
problem (likely a bug).

Let's suppose I am running replica exchange with -maxh, -replex 50
and neighbour searching frequence = 5 steps .

If I well understood, once the code run for maxh*0.99 it stops at the next
neighbour searching step.

If the program reaches maxh*0.99 let's say at the step 50, the
next neighbour searching step is the 55. But if 2 replicas exchange at step
50, it implies rebuilding the neighbour searching
( because in the code bExchanged=TRUE implies bNS to be TRUE).

These two replicas so stop at step 51 but the other replicas continue until
the 55th step.
Here the problem appears. In this case mdrun performs global communication
calling compute_global next to the line commented as:
 /* ############## IF NOT VV, Calculate globals HERE, also iterate
constraints  ############ */

Since the 2 replicas that exchanged already ended, mdrun hungs.

Maybe my analysis is incorrect and in this case I apologize.
In any case, if nobody did, I am looking for a fix.

Francesco
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