[petsc-users] Petcs preconditioners

[Edoardo alinovi]

Dear users,

Since this mailing list has already solved  one of my problem, I would like
to take advantage of your knowlege one more time (thank you so much!).

I am a new user (Fortran) and, as you can imagine, I have a lot of
questions.

Actually, some of them are about preconditioners. In particular I would
like to ask:

- 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?

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

-  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?

Every hint will be very appreciated.

Thank you very much and sorry for the newby questions,

Edoardo
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