[petsc-users] Copying PETSc Objects Across MPI Communicators

[Damyn Chipman]

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?

-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

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