[petsc-users] Clarification on PCASMSetLocalSubdomain is and is_local

[Matthew Knepley]

On Thu, Jun 2, 2016 at 5:27 PM, Luc Berger-Vergiat <lb2653 at columbia.edu>
wrote:

> Ok I get it,  then if I have multiple subdomains on the local processor is
> and is_local will be arrays of is that represent each subdomain on that
> processor?
>

Yep.

  Matt


> Best,
> Luc
>
> On 06/02/2016 06:21 PM, Matthew Knepley wrote:
>
> On Thu, Jun 2, 2016 at 5:11 PM, Luc Berger-Vergiat < <lb2653 at columbia.edu>
> lb2653 at columbia.edu> wrote:
>
>> Hi all,
>> I would like a quick clarification on what is and is_local are
>> representing in the PCASMSetLocalSubdomains().
>> My understanding is that if I have two mpi ranks and four subdomains I
>> can end up having four blocks that I can denote as follows:
>>
>>            |   domain1  |  domain2  |  domain3  |  domain3   |
>> rank1  |    block11  |    block12  |   block13   | |
>> rank2  |    block21  |    block22  |       --         |    block24 |
>>
>> to each blockIJ I associate isIJ.
>>
>> So for rank1 I will have is=[1,2,3] and is_local=[is11,is12,is13], and
>> for rank2 I will have is=[1,2,4] and is_local=[is21,is22,is24].
>> Or am I not understanding things correctly?
>
>
> I did not understand the above.
>
> The best way to think of this is algebraically. Suppose you have a matrix
> A, and you divide the rows into k disjoint sets where each
> process gets one set. Then is_local on each process is a list of the rows
> in that set. Now we also allow some overlap, which means
> rows in other sets are also used. The is on each process contains both
> is_local and these extra rows from other sets.
>
>   Thanks,
>
>      Matt
>
>
>>
>> --
>> Best,
>> Luc
>>
>>
>>
>
>
> --
> 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
>
>
> --
> Best,
> Luc
>
>


-- 
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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