Non repetability issue and difference between 2.3.0 and 2.3.3

[Matthew Knepley]

On Wed, Sep 24, 2008 at 11:21 AM, Etienne PERCHAT
<etienne.perchat at transvalor.com> wrote:
> Dear Petsc users,
>
>
>
> I come again with my comparisons between v2.3.0 and v2.3.3p8.
>
>
>
> I face a non repeatability issue with v2.3.3 that I didn't have with v2.3.0.
>
> I have read the exchanges made in March on a related subject but in my case
> it is at the first linear system solution that two successive runs differ.
>
>
>
>
>
> It happens when the number of processors used is greater than 2, even on a
> standard PC.
>
> I am solving MPIBAIJ symmetric systems with the Conjugate Residual method
> preconditioned ILU(1) and Block Jacobi  between subdomains.
>
> This system is the results of a FE assembly on an unstructured mesh.
>
>
>
> I made all the runs using -log_summary and -ksp_truemonitor.
>
>
>
> Starting with the same initial matrix and RHS, each run using 2.3.3p8
> provides slightly different results while we obtain exactly the same
> solution with v2.3.0.
>
>
>
> With Petsc 2.3.3p8:
>
>
>
> Run1:   Iteration= 68      residual= 3.19515221e+000       tolerance=
> 5.13305158e+000 0
>
> Run2:    Iteration= 68     residual= 3.19588481e+000       tolerance=
> 5.13305158e+000 0
>
> Run3:    Iteration= 68     residual= 3.19384417e+000       tolerance=
> 5.13305158e+000 0
>
>
>
> With Petsc 2.3.0:
>
>
>
> Run1:   Iteration= 68      residual= 3.19369843e+000       tolerance=
> 5.13305158e+000 0
>
> Run2:   Iteration= 68      residual= 3.19369843e+000       tolerance=
> 5.13305158e+000 0
>
>
>
> If I made a 4proc run with a mesh partitioning such that any node could be
> located on more than 2 proc. I did not face the problem.

It is not clear whether you have verified that on different runs, the
partitioning is
exactly the same.

  Matt

> I first thought about a MPI problem related to the order in which messages
> are received and then summed.
>
> But it would have been exactly the same with 2.3.0 ?
>
>
>
> Any tips/ideas ?
>
>
>
> Thanks by advance.
>
> Best regards,
>
>
>
> Etienne Perchat



-- 
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