[petsc-users] Petcs preconditioners

[Stefano Zampini]

>
>
> - I'm dealing with matrices that change the value of the coeffs in time,
> but maintain the same zero pattern. Is it possible to create a ksp (linear
> solver + preconditioner) object before the time loop and pass it to the
> solver subroutine, avoiding the construction/destruction every iteration?
> In this case, is the preconditioner updated each iteration?
>
>
Just call KSPSetOperators evry time the matrix get updated. PETSc
preconditioners are aware of any nonzero pattern / matrix value changes


> - Is the ILU suitable for parallel matrix format (MPIAIJ)? Is there in
> petsc the  DILU (diagonal ILU) preconditioner?
>

Petsc does not have a parallel ILU. Default is block Jacoby, with ILU(0) on
the diagonal blocks. Is this DILU?

>
> -  I would like to use a multigrid preconditioner. Is it better to use
> GAMG or boomerAMG in your opinion? In the manual there are a lot of options
> that create a mess in my head... Would you so kind to post a standard
> example of settings for GAMG/boomerAMG?
>
>
What is the problem you are solving? For now, you can just select boomerAMG
(-pc_type hypre) or GAMG a(-pc_type gamg) at command line and you can start
experimenting with their options. Depdending on the structure of your
problem, you may need extra customizations (e.g MatSetNearNullSpace for
passing rigid body modes for elasticity)


> Every hint will be very appreciated.
>
> Thank you very much and sorry for the newby questions,
>
> Edoardo
>



-- 
Stefano
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