[petsc-users] Get solution and rhs in the ts monitor

[Tang, Qi]

Thanks a lot, that works. This confirms that I can reproduce the rhs I need.


On Nov 10, 2022, at 9:15 AM, Stefano Zampini <stefano.zampini at gmail.com> wrote:

 -ksp_view_mat
-ksp_view_rhs
-ksp_view_solution

On Nov 10, 2022, at 5:00 PM, Tang, Qi <tangqi at msu.edu<mailto:tangqi at msu.edu>> wrote:

Yes, but I need to get A, x and b out, so that I can test them in pyamg for other preconditioner options. I can get A, x, and b through what I described, but I do not think x or b is the original one in the linear system.

Is there a simple way to get x and b (I just need once) of TS? Thanks.

Qi
________________________________
From: Matthew Knepley <knepley at gmail.com<mailto:knepley at gmail.com>>
Sent: Thursday, November 10, 2022 6:15 AM
To: Tang, Qi <tangqi at msu.edu<mailto:tangqi at msu.edu>>
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] Get solution and rhs in the ts monitor

On Thu, Nov 10, 2022 at 3:18 AM Tang, Qi <tangqi at msu.edu<mailto:tangqi at msu.edu>> wrote:
Hi,

How could I get rhs and solution in a ksp solve of ts?

I am testing a linear problem (TS_Linear) using a bdf integrator. I tried to get the operator, rhs, and solution in the ts monitor through TSGetKSP and KSPGet***. But r = Ax-b is much larger than the ksp norm. I know the solver works fine.

Ax - b is the _unpreconditioned_ norm. By default we are printing the preconditioned norm. You can see the difference by running with

  -ksp_monitor_true_residual

  Thanks,

     Matt

Did I misunderstand something about how TS works here? Perhaps one of the vectors is changed after the ksp solve? If so, is there a simple way to get rhs and solution that ksp of ts solved?

Thanks,
Qi




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