[petsc-users] ParMETIS question

[Matthew Knepley]

On Tue, Dec 21, 2010 at 5:49 AM, Thomas Witkowski <
thomas.witkowski at tu-dresden.de> wrote:

> Hi,
>
> I have a not directly PETSc related question, but I hope to get some answer
> from the community here. In my FEM code, I make use of ParMETIS to partition
> the mesh. I make direct use of this library and not of PETSc's ParMETIS
> integration. The initial partition is always fine, but I use the
> ParMETIS_V3_AdaptiveRepart function for repartition the mesh due to local
> mesh adaption. In most cases, the result is fine, but there are two points,
> where I have trouble with:
>
> 1) Sometimes ParMETIS generates empty partitions, i.e., a processor has
> zero mesh elements. This is something my code cannot handle. Is this a bug
> or a feature? If it is a feature, is there any possiblity to disable it?
>

ParMetis has a balance constraint if you weight vertices. This will enforce
equal size partitions.


> 2) In most cases the specific partitions are not connected. If I put all
> data to ParMETIS in a correct way, is this okay? My code can handle it, but
> is slows down the computation due to larger interior boundaries and
> therefore to more communications.
>

ParMetis minimizes the overall boundary size, so I do not understand how you
could see this slowdown.

   Matt


> Does anyone of you know an answer to these question? Is there a debug mode
> in ParMETIS, where I can see which data is set to its function calls?
>
> Regards,
>
> Thomas
>



-- 
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
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