[petsc-dev] About parallel of ILU

[Matthew Knepley]

On Tue, Feb 9, 2021 at 4:30 AM Chen Gang <569615491 at qq.com> wrote:

> Dear Professor,
>
> I have a question about the bjacobi+ilu, I'm in the place
>
> src/ksp/ksp/tutorials
>
> and running the ex2 with
>
> mpirun -np 40 -bind-to core ./ex2 -m 2000 -n 2000  -ksp_max_it 1000000
> -ksp_rtol 1e-10 -ksp_type gmres -pc_type bjacobi -sub_pc_type ilu
> -sub_pc_factor_levels 10 -ksp_monitor_short
>
> on the Intel machine with 40 cores, the petsc is complied with MKL and
> ICC/MPIICC with O3.
>
> I found the numerical results are not the same from time to time, although
> they all right, the iterations are not exactly the same from time to time.
> Where have I done wrong?
>

MPI does not guarantee the order that reductions are calculated, so that
you can get slightly different answers in parallel.

  Thanks,

      Matt


> I'm looking forward to hear you!
>
> Best,
>
> Gang Chen
>
> Sichuan Univertsity,
> School of Mathematics,
> Chengdu, China
>


-- 
What most experimenters take for granted before they begin their
experiments is infinitely more interesting than any results to which their
experiments lead.
-- Norbert Wiener

https://www.cse.buffalo.edu/~knepley/ <http://www.cse.buffalo.edu/~knepley/>
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