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

[Barry Smith]

   What about a PETSC_COMM_DEFAULT that lives in the same place as
PETSC_COMM_WORLD and PETSC_COMM_SELF.? You could have it
default to PETSC_COMM_whatever and the user could change it
immediately after PetscInitialize() to whatever they chose.

   For simplicity I wouldn't have a setter like PetscSetDefaultComm()  
rather
I would just have the user set it directly, e.g. PETSC_COMM_DEFAULT =  
mynewcomm


    Barry

If we ever did a proper C++ wrapper, we could use the same idea



On Aug 25, 2008, at 10:54 AM, Lisandro Dalcin 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)
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>