[petsc-users] (no subject)

[Dave May]

I think to achieve what you want you will need to use a KSP which supports
right preconditioning, that is they monitor || Ax-b || rather than ||
P^{-1} ( Ax - b ) ||, where P^{-1} is the application of the preconditioner.

Try running with -ksp_type fgmres or -ksp_type gcr. These Krylov methods
support right preconditioning by default.

Thanks,
Dave

On Mon 22. Jul 2024 at 04:37, Константин Мурусидзе <
konstantin.murusidze at math.msu.ru> wrote:

> Good afternoon. I am a student at the Faculty of Mathematics and for my
> course work I need to solve SLAE with a relative accuracy of 1e-8 or more.
> To do this, I created the function PetscCall(KSPSetTolerances(ksp, 1. e-8,
> PETSC_DEFAULT, PETSC_DEFAULT,
> ZjQcmQRYFpfptBannerStart
> This Message Is From an External Sender
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> ZjQcmQRYFpfptBannerEnd
> Good afternoon. I am a student at the Faculty of Mathematics and for my
> course work I need to solve SLAE with a relative accuracy of 1e-8 or more.
> To do this, I created the function PetscCall(KSPSetTolerances(ksp, 1.e-8,
> PETSC_DEFAULT, PETSC_DEFAULT, 100000));. But in the end, only 38 iterations
> were made and the relative norm ||Ax-b||/||b|| it turns out 4.54011. If you
> reply to my email, I can give you more information about the solver
> settings.
>
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