[petsc-users] (no subject)

[Barry Smith]

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.murusidze at math.msu.ru> wrote:
> 
> After this procedure I saw "Linear solution did not converge due to DIVERGED_INDEFINITE_MAT". Then as shown on https://urldefense.us/v3/__https://petsc.org/main/manualpages/KSP/KSP_DIVERGED_INDEFINITE_PC/__;!!G_uCfscf7eWS!dUAb2JB1g_tVNhPsjMe6qIzyNarGnl8HzZh2cOn_IkzWnHD5QJPY06dL8iwmKAJH2A_CYwssOq3IcWT2ButJOns$ ​  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" <bsmith at 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.murusidze at math.msu.ru <mailto:konstantin.murusidze at math.msu.ru>> wrote:
> 
> This Message Is From an External Sender
> This message came from outside your organization.
> 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.
> 

-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.mcs.anl.gov/pipermail/petsc-users/attachments/20240805/1a5b41d3/attachment.html>