[petsc-users] KSPComputeRitz, GMRES, matrix with complex number

[feng wang]

Thanks for the clarification. any recommendations to get around this?

I am solving a set of linear systems of A_i x_i = B_i with matrix-based GMRES. The entries of A_i and B_i are complex numbers. It is pre-conditioned with ASM and the preconditioning matrix is A_i itself. I would like to show the Ritz value to understand the convergence behaviour for each A_i x_i = B_i.
________________________________
From: Mark Adams <mfadams at lbl.gov>
Sent: 14 July 2022 14:16
To: feng wang <snailsoar at hotmail.com>
Cc: petsc-users at mcs.anl.gov <petsc-users at mcs.anl.gov>
Subject: Re: [petsc-users] KSPComputeRitz, GMRES, matrix with complex number

No. I missed that note.
Complex has not been implemented.


On Thu, Jul 14, 2022 at 9:54 AM feng wang <snailsoar at hotmail.com<mailto:snailsoar at hotmail.com>> wrote:
Hi Mark,

Thanks for your reply!

Maybe I have a misunderstanding of the documentation of KSPComputeRitz (https://petsc.org/main/docs/manualpages/KSP/KSPComputeRitz/).  It says "-this is currently not implemented when PETSc is built with complex numbers".

But if it works, I will give it a try.

Thanks,
Feng


<https://petsc.org/main/docs/manualpages/KSP/KSPComputeRitz/>

________________________________
From: Mark Adams <mfadams at lbl.gov<mailto:mfadams at lbl.gov>>
Sent: 14 July 2022 12:23
To: feng wang <snailsoar at hotmail.com<mailto:snailsoar at hotmail.com>>
Cc: petsc-users at mcs.anl.gov<mailto:petsc-users at mcs.anl.gov> <petsc-users at mcs.anl.gov<mailto:petsc-users at mcs.anl.gov>>
Subject: Re: [petsc-users] KSPComputeRitz, GMRES, matrix with complex number

Why do you say it only works with Real? You need to configure PETSc to use complex numbers and it should work.
This is an advanced method and it does not have any tests, which basically says it is very experimental.
Don't expect it to be very robust.

Mark

On Thu, Jul 14, 2022 at 7:19 AM feng wang <snailsoar at hotmail.com<mailto:snailsoar at hotmail.com>> wrote:
Dear All,

I am using GMRES with complex numbers and would like to compute the Ritz values. I am looking at KSPComputeRitz<https://petsc.org/main/docs/manualpages/KSP/KSPComputeRitz/>  and it seems to me that it only works with Petsc compiled with real numbers. Is there an easy alternative way to compute Ritz values for matrices with complex numbers?

Thanks,
Feng
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