[petsc4py] What should be the 'default' communicator?

[Matthew Knepley]

I would still maintain that PETSC_COMM_WORLD is the correct default. There
are better paradigms for embarassingly parallel operation, like Condor. PETSc
is intended for parallel, domain decomposition runs.

   Matt

On Mon, Aug 25, 2008 at 10:54 AM, Lisandro Dalcin <dalcinl at gmail.com> wrote:
> After working hard on mpi4py, this week I'll spend my time cleaning-up
> and adding features to the new Cython-based petsc4py. Then, I'll be
> asking questions to this list requesting for advise.
>
> In all calls that create new PETSc objects, I've decided to make the
> 'comm' argument optional. If the communicator is not passed,
> PETSC_COMM_WORLD is currently used. This is the approach PETSc uses in
> some C++ calls implemented through PetscPolymorphicFunction().
>
> But now I believe that is wrong, and that PETSC_COMM_SELF should be
> the default. Or perhaps even better, I should let users set the
> default communicator used by petsc4py to create new (parallel)
> objects.
>
> An anecdote: some time ago, a petsc4py user wrote a sequential code
> and created objects without passing communicator arguments, next he
> wanted to solve many of those problems in different worker processes
> in a "ambarrasingly parallel" fashion and collect results at the
> master process. Of course, he run into trouble. Then I asked him to
> initialize PETSc in such a way that PETSC_COMM_WORLD was actually
> PETSC_COMM_SELF (by setting the world comm before PetscInitalize()).
> This mostly works, but has a problem: we have lost the actual
> PETSC_COMM_WORLD, so we are not able to create a parallel object after
> PetscInitialize().
>
> Any thoughts?
>
>
> --
> Lisandro Dalcín
> ---------------
> Centro Internacional de Métodos Computacionales en Ingeniería (CIMEC)
> Instituto de Desarrollo Tecnológico para la Industria Química (INTEC)
> Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET)
> PTLC - Güemes 3450, (3000) Santa Fe, Argentina
> Tel/Fax: +54-(0)342-451.1594
>
>



-- 
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