Re: [petsc-users] (no subject)

Константин Мурусидзе Mon, 05 Aug 2024 11:28:16 -0700

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I know that matrix is symmetric, but it isn’t positive definite. Is it possible to solve such problem, maybe with another solver or preconditioner?

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Отправлено из мобильной Яндекс Почты

05.08.2024, 18:51, "Barry Smith" <bsm...@petsc.dev>:

PCFactorSetShiftType() only works for certain preconditioners, ILU.

If the matrix is not symmetric it also doesn't help.

Are you sure the matrix is symmetric positive definite?

On Aug 5, 2024, at 4:43 AM, Константин Мурусидзе <konstantin.murusi...@math.msu.ru> wrote:

After this procedure I saw "Linear solution did not converge due to DIVERGED_INDEFINITE_MAT". Then as shown on https://petsc.org/main/manualpages/KSP/KSP_DIVERGED_INDEFINITE_PC/ I wrote such line PetscCall(PCFactorSetShiftType(pc, MAT_SHIFT_POSITIVE_DEFINITE)); but nothing changed and I still have divergence

22.07.2024, 17:22, "Barry Smith" <bsm...@petsc.dev>:

Run with -ksp_monitor_true_residual -ksp_converged_reason -ksp_view to see why it is stopping at 38 iterations.

Barry

On Jul 22, 2024, at 7:37 AM, Константин Мурусидзе <konstantin.murusi...@math.msu.ru> wrote:

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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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