[petsc-users] R: AMG Variable block preconditioner

[Jed Brown]

Smoothed aggregation mostly just cares about the near-null space
(MatSetNearNullSpace), which is a global property.  Classical AMG uses
block size directly (number of dofs per C-point), but I'm not aware of
any implementation that supports variable block size.  This would be a
research topic.

Marco Cisternino via petsc-users <petsc-users at mcs.anl.gov> writes:

> Hi Stefano,
> thanks for your interest.
> Mainly, elliptic operators both in the context of methods in NS solvers and in the context of mesh deformation.
> I didn't think about AMG on each block. What I was thinking about is an AMG preconditioner aware about the variable size blocks.
> I hope it is clearer than before.
> Thanks,
>
>
> Marco Cisternino, PhD
> marco.cisternino at optimad.it
> _______________________________
> OPTIMAD Engineering srl
> Via Giacinto Collegno 18, Torino, Italia.
> +3901119719782
> www.optimad.it
>
>
> ________________________________________
> Da: Stefano Zampini <stefano.zampini at gmail.com>
> Inviato: lunedì 28 ottobre 2019 17:09
> A: Marco Cisternino
> Cc: petsc-users
> Oggetto: Re: [petsc-users] AMG Variable block preconditioner
>
> Marco,
>
> you should define what do you mean by "AMG block preconditioning"; separate AMG on each block? What operator do you plan to precondition?
> AFAIK, MatSetVariableBlockSizes is just exploited by the Jacobi solver .
>
> Thanks
> Stefano
>
> Il giorno lun 28 ott 2019 alle ore 19:05 Marco Cisternino via petsc-users <petsc-users at mcs.anl.gov<mailto:petsc-users at mcs.anl.gov>> ha scritto:
> Hello everybody.
> We would like to setup an algebraic multi-grid block preconditioner and I would like to be able to define custom blocks of variable sizes. Reading the documentation, it seems that this can be achieved using the "PCGAMG" preconditioner and defining the blocks with the function "MatSetVariableBlockSizes". Is this correct?
> Are the variable blocks exploited by PCGAMG algorithms? We suppose this PC structure is already exploited in PCVPBJACOBI.
> Are the different options like PCHYPRE (setting "-pc_hypre_type" to "boomeramg") suitable for AMG preconditioner with variable size blocks?
> If none of the above solutions are available, could anyone suggest any other strategy in order to get a preconditioner like this using PETSc?
> Any help is much appreciated.
> Thanks.
>
> Best regards,
>
> Marco Cisternino
>
>
> --
> Stefano