[petsc-users] Matrix version of VecScatterCreateToAll

[Matthew Knepley]

On Sun, Dec 18, 2022 at 9:44 AM 김성익 <ksi2443 at gmail.com> wrote:

> For example, before using preallocaotor, I made A matrix. (A matrix has
> information about indices of global matrix)
> And the code structures are as below.
> for (int i=0; i<num; i++){
>    MatGetRow(A,~~) // for getting indices info of global matrix.
>    MatSetvalues(preallocator, value_from_A);
> }
> Current state, I got an error at 'MatGetRow' when I run this code in
> parallel.
> That's why I want "all mpi ranks has information of A matrix".
>

Just from your explanation, this does not sound like a scalable algorithm
for this, and FEM should be scalable.
I would take a look at some parallel FEM codes before settling on this
structure.

However, if you really wish to do this, you can create the original matrix
and then call

  https://petsc.org/main/docs/manualpages/Mat/MatCreateSubMatrices/

with every process giving all indices as the argument.

  Thanks,

    Matt


> Thanks,
> Hyung Kim
>
>
> 2022년 12월 18일 (일) 오후 11:36, Junchao Zhang <junchao.zhang at gmail.com>님이 작성:
>
>> I am not clear on what you said "this information must be viewed in all
>> mpi ranks."  Even with preallocator, each rank only needs to insert entries
>> it knows (i.e., don't need to get all entries)
>>
>> Maybe you could provide an example code for us to better understand what
>> you mean?
>>
>> --Junchao Zhang
>>
>>
>> On Sun, Dec 18, 2022 at 8:25 AM 김성익 <ksi2443 at gmail.com> wrote:
>>
>>> Hello,
>>>
>>>
>>> Is there a matrix version function of VecScatterCreateToAll?
>>>
>>> I'm using preallocator for preallocation of global matrix.
>>> Prior to using the preallocator, information related to allocation is
>>> stored in the specific matrix, and this information must be viewed in all
>>> mpi ranks.
>>> For using preallocator, I need scattering the specific matrix info to
>>> all mpi ranks.
>>>
>>> Thanks,
>>> Hyung Kim
>>>
>>

-- 
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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