[petsc-users] `VecCreateGhostWithArray` ownership layout vs application indices after migrate

[Miguel Molinos]

Thank you Matt, your answer helps a lot!

Miguel


> On 17 Jul 2026, at 14:41, Matthew Knepley <knepley at gmail.com> wrote:
> 
> On Fri, Jul 17, 2026 at 8:37 AM Miguel Molinos <m.molinos at upm.es <mailto:m.molinos at upm.es>> wrote:
>> Dear all,
>> 
>> I am using "VecCreateGhostWithArray" to wrap particle fields (positions, densities, etc.) stored in a “DMSwarm" structure. On each rank the local array is packed as [owned particles | ghost particles].
>> 
>> My understanding from the implementation in pbvec.c is:
>> 
>> 1. “PetscSplitOwnership" + "VecSetSizes(n, N)" assigns each rank a contiguous ownership range [rstart, rstart+n).
>> 2. Local owned entry "I" therefore corresponds to global index "rstart + I".
>> 3. The ghosts[] array in “ VecCreateGhostWithArray" must contain those PETSc global vector indices, because “VecGhostUpdate" scatters from the global vector into the local ghost padding.
>> 
>> Is that correct?
> 
> Yes.
>  
>> If so, after rebalancing particles with “DMSwarmMigrate", the application “AO" numbering attached to each particle is no longer the same as the contiguous ownership of a newly created ghosted Vec. In that case, should one always renumber the owned particle ids to "rstart + I" (and let ghosts inherit those ids) before calling “VecCreateGhostWithArray"?
> 
> Ah, yes this is true. We had never used them in this way. A particle keeps its "id" field throughout its life, so maybe it would make sense to have a "local id" that changed after Migrate().
> 
>   Thanks,
> 
>      Matt
>  
>> Thanks,  
>> Miguel
>> 
>> Miguel Molinos
>> 
>> Escuela de Ingenieros de Caminos, Canales y Puertos
>> Dep. Mecánica Medios Continuos y Teoría de Estructuras
>> 
>> Prof. Aranguren, 3 - Ciudad Universitaria.
>> Planta 9. 28040, Madrid
>> 
>> 
>> 
> 
> 
> 
> --
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> -- Norbert Wiener
> 
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