[petsc-users] Copying PETSc Objects Across MPI Communicators

[Jose E. Roman]

Currently MATSCALAPACK does not support MatCreateSubMatrix(). I guess it would not be difficult to implement.

Jose


> El 27 oct 2023, a las 21:53, Damyn Chipman <damynchipman at u.boisestate.edu> escribió:
> 
> Yeah, I’ll make an issue and use a modified version of this test routine.
> 
> Does anything change if I will be using MATSCALAPACK matrices instead of the built in MATDENSE? Like I said, I will be computing Schur complements and need to use a parallel and dense matrix format.
> 
> -Damyn
> 
>> On Oct 26, 2023, at 10:01 AM, Matthew Knepley <knepley at gmail.com> wrote:
>> 
>> On Wed, Oct 25, 2023 at 11:55 PM Damyn Chipman <damynchipman at u.boisestate.edu> wrote:
>> Great thanks, that seemed to work well. This is something my algorithm will do fairly often (“elevating” a node’s communicator to a communicator that includes siblings). The matrices formed are dense but low rank. With MatCreateSubMatrix, it appears I do a lot of copying from one Mat to another. Is there a way to do it with array copying or pointer movement instead of copying entries?
>> 
>> We could make a fast path for dense that avoids MatSetValues(). Can you make an issue for this? The number one thing that would make this faster is to contribute a small test. Then we could run it continually when putting in the fast path to make sure we are preserving correctness.
>> 
>>   Thanks,
>> 
>>     Matt
>>  
>> -Damyn
>> 
>>> On Oct 24, 2023, at 9:51 PM, Jed Brown <jed at jedbrown.org> wrote:
>>> 
>>> You can place it in a parallel Mat (that has rows or columns on only one rank or a subset of ranks) and then MatCreateSubMatrix with all new rows/columns on a different rank or subset of ranks.
>>> 
>>> That said, you usually have a function that assembles the matrix and you can just call that on the new communicator.
>>> 
>>> Damyn Chipman <damynchipman at u.boisestate.edu> writes:
>>> 
>>>> Hi PETSc developers,
>>>> 
>>>> In short, my question is this: Does PETSc provide a way to move or copy an object (say a Mat) from one communicator to another?
>>>> 
>>>> The more detailed scenario is this: I’m working on a linear algebra solver on quadtree meshes (i.e., p4est). I use communicator subsets in order to facilitate communication between siblings or nearby neighbors. When performing linear algebra across siblings (a group of 4), I need to copy a node’s data (i.e., a Mat object) from a sibling’s communicator to the communicator that includes the four siblings. From what I can tell, I can only copy a PETSc object onto the same communicator.
>>>> 
>>>> My current approach will be to copy the raw data from the Mat on one communicator to a new Mat on the new communicator, but I wanted to see if there is a more “elegant” approach within PETSc.
>>>> 
>>>> Thanks in advance,
>>>> 
>>>> Damyn Chipman
>>>> Boise State University
>>>> PhD Candidate
>>>> Computational Sciences and Engineering
>>>> damynchipman at u.boisestate.edu
>> 
>> 
>> 
>> -- 
>> 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/
>