[petsc-users] Domain partitioning using DAs

[Mohamad M. Nasr-Azadani]

Thanks Barry and Jed.

That definitely helps.

Best,
Mohamad


On Sat, Oct 8, 2011 at 6:32 AM, Jed Brown <jedbrown at mcs.anl.gov> wrote:

> On Sat, Oct 8, 2011 at 07:27, Mohamad M. Nasr-Azadani <mmnasr at gmail.com>wrote:
>
>> Thanks Jed. I guess the whole point I am missing is in that "squarish".
>> I, for instance, use two processors for a domain of the global size:
>> nx=50
>> ny=40
>> nz=4
>>
>> To my surprise, the way it was decomposed was in y-direction, i.e.
>> processor 0:
>> 0-49
>> 0-19
>> 0-3
>>
>> processor 1:
>> 0-49
>> 20-39
>> 0-3
>>
>> and not x-direction which minimizes the surface area between the two
>> processors.
>> Obviously "2" is a prime number. In that case, is PETSc biased to choose
>> any of the directions?
>>
>
> There is an order to which directions get tried, but it will never pick a
> split that is "too bad". If you run on four processes, it will split in both
> the X and Y directions. The complete code is here.
>
>
> http://www.mcs.anl.gov/petsc/petsc-as/snapshots/petsc-dev/src/dm/impls/da/da3.c.html#line231
>
> I'm a little surprised it doesn't find the "best" split in this simple
> case.
>
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