[Pw_forum] bug in mm_dispersion.f90

[Gabriele Sclauzero]

Dear Javier,

Javier Fuhr wrote:
> Hi,
> I think I've found a bug in the calculation of the dispersion 
> energy/force/stress when doing a parallel calculation with more than one 
> pool. In mm_dispersion.f90, the sum between the processes is only done 
> intra_pool but not inter_pool.

   I don't know that (pretty new) part of the code, but at a first glance to that 
subroutine I would say that you must be wrong.
The parallelization is done inside each pool over atoms, hence you only need to collect 
the partial sums over subsets of atoms from the processes in the pool.
Using more than one pool will not improve the speedup of that part of the code, but 
neither change the result of energy_london.

If you have (reproducible) evidence that the same calculation performed with more than one 
pool gives a different result, please provide some simple input file.

Thanks,

GS


> Here is a diff between the version 4.1 and a possible corrected one (I'm 
> not an expert in the paralelization of QE...):
> -----------------------------
> 261c261
> <     USE mp_global,    ONLY : mpime , nproc , intra_pool_comm
> ---
>  >     USE mp_global,    ONLY : mpime , nproc , intra_pool_comm, 
> inter_pool_comm
> 362a363
>  >       CALL mp_sum ( energy_london , inter_pool_comm )
> 377c378
> <     USE mp_global,    ONLY : mpime , nproc , intra_pool_comm
> ---
>  >     USE mp_global,    ONLY : mpime , nproc , intra_pool_comm, 
> inter_pool_comm
> 503a505
>  >       CALL mp_sum ( force_london , inter_pool_comm )
> 519c521
> <     USE mp_global,    ONLY : mpime , nproc , intra_pool_comm
> ---
>  >     USE mp_global,    ONLY : mpime , nproc , intra_pool_comm, 
> inter_pool_comm
> 660a663
>  >       CALL mp_sum ( stres_london , inter_pool_comm )
> -----------------------------
> 
> Regards,
> Javier
> 
> -- 
> Dr. Javier Daniel Fuhr
> Grupo Física de Superficies - Div. Colisiones Atómicas
> Centro Atómico Bariloche
> Bariloche - Argentina
> TE : ++54 2944 44 5100  Int. 5524
> FAX: ++54 2944 44 5299
> 
> 
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| Gabriele Sclauzero, PhD Student                  |
| c/o:   SISSA & CNR-INFM Democritos,              |
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