[petsc-users] What does PCASMSetOverlap do?

[Matthew Knepley]

On Wed, Apr 13, 2022 at 6:42 AM Mark Adams <mfadams at lbl.gov> wrote:

> No, without overlap you have, let say:
> core 1:   1:32, 1:32
> core 2:   33:64,  33:64
>
> Overlap will increase the size of each domain so you get:
> core 1:   1:33, 1:33
> core 2:   32:65,  32:65
>

I do not think this is correct. Here is the algorithm. Imagine the matrix
is a large graph. When you divide rows, you
can think of that as dividing the vertices into sets. If overlap = 1, it
means start with my vertex set, and add all vertices
that are just 1 edge away from my set.

  Thanks,

     Matt


> What you want is reasonable but requires PETSc to pick a separator set,
> which is not well defined.
> You need to build that yourself with gasm (I think) if you want this.
>
> Mark
>
> On Wed, Apr 13, 2022 at 3:17 AM Zhuo Chen <chenzhuotj at gmail.com> wrote:
>
>> Hi,
>>
>> I hope that everything is going well with everybody.
>>
>> I have a question about the PCASMSetOverlap. If I have a 128x128 matrix
>> and I use 4 cores with overlap=1. Does it mean that from core 1 to core 4,
>> the block ranges are (starting from 1):
>>
>> core 1:   1:33, 1:33
>> core 2:   33:65,  33:65
>> core 3:   65:97,  65:97
>> core 4:   95:128, 95:128
>>
>> Or is it something else? I cannot tell from the manual.
>>
>> Many thanks in advance.
>>
>>
>>
>> --
>> Zhuo Chen
>> Department of Astronomy
>> Tsinghua University
>> Beijing, China 100084
>> *https://czlovemath123.github.io/ <https://czlovemath123.github.io/>*
>>
>

-- 
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

https://www.cse.buffalo.edu/~knepley/ <http://www.cse.buffalo.edu/~knepley/>
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