[petsc-users] "-ts_exact_final_time matchstep" leads to DIVERGED_STEP_REJECTED

[Blondel, Sophie]

Hi everyone,

The first max time it is trying to reach is 1.0e-12 s, and the initial dt is set to 1.0e-12 s from the commandline options. I believe it's not a formatting issue and that the dt is actually set somewhere to 0 s because that's why the step is rejected.

Best,

Sophie
________________________________
From: Barry Smith <bsmith at petsc.dev>
Sent: Friday, December 13, 2024 14:21
To: Blondel, Sophie <sblondel at utk.edu>; Jed Brown <jed at jedbrown.org>; Zhang, Hong <hongzhang at anl.gov>; Emil Constantinescu <emconsta at anl.gov>
Cc: petsc-users at mcs.anl.gov <petsc-users at mcs.anl.gov>; xolotl-psi-development at lists.sourceforge.net <xolotl-psi-development at lists.sourceforge.net>
Subject: Re: [petsc-users] "-ts_exact_final_time matchstep" leads to DIVERGED_STEP_REJECTED


   Hm, what is the final time you are stepping towards in this run?

   There is something wrong with the adapt code since it seems to start with a dt of 0 but then tries "adapting" several times, but it could be the
monitor function does not correctly format numbers smaller than 1.e-12 and it is just using truly small dt.

   Jed, Hong, Emil?

   Barry


On Dec 10, 2024, at 11:08 AM, Blondel, Sophie <sblondel at utk.edu> wrote:

Good morning Barry,

Attached are the updated files, there is more useful information in them.

Cheers,

Sophie
________________________________
From: Blondel, Sophie via Xolotl-psi-development <xolotl-psi-development at lists.sourceforge.net<mailto:xolotl-psi-development at lists.sourceforge.net>>
Sent: Monday, December 9, 2024 17:29
To: Barry Smith <bsmith at petsc.dev<mailto:bsmith at petsc.dev>>
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>>; xolotl-psi-development at lists.sourceforge.net<mailto:xolotl-psi-development at lists.sourceforge.net> <xolotl-psi-development at lists.sourceforge.net<mailto:xolotl-psi-development at lists.sourceforge.net>>
Subject: Re: [Xolotl-psi-development] [petsc-users] "-ts_exact_final_time matchstep" leads to DIVERGED_STEP_REJECTED

Hi Barry,

I hope you are doing well.

Attached are the output. To give a little more context, this is a "new" way of running the code where multiple instances are created and communicate together every few time steps (like coupling the code with itself in memory). Here there are 3 instances that each have a separate TS object, plus one "main" instance that doesn't solve anything but compute rates to exchange between the other instances.

Cheers,

Sophie
________________________________
From: Barry Smith <bsmith at petsc.dev<mailto:bsmith at petsc.dev>>
Sent: Monday, December 9, 2024 15:12
To: Blondel, Sophie <sblondel at utk.edu<mailto:sblondel at utk.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>>; xolotl-psi-development at lists.sourceforge.net<mailto:xolotl-psi-development at lists.sourceforge.net> <xolotl-psi-development at lists.sourceforge.net<mailto:xolotl-psi-development at lists.sourceforge.net>>
Subject: Re: [petsc-users] "-ts_exact_final_time matchstep" leads to DIVERGED_STEP_REJECTED



On Dec 9, 2024, at 2:56 PM, Blondel, Sophie via petsc-users <petsc-users at mcs.anl.gov<mailto:petsc-users at mcs.anl.gov>> wrote:

Hi,

I am trying to understand a strange behavior I'm encountering: when running my application with "-ts_exact_final_time stepover" everything goes well, but when I switch to "matchstep" I get DIVERGED_STEP_REJECTED before the first time step is finished.

   This is in the very first time-step in TSSolve?

    Please run with -ts_monitor and send all the output (best for a short time interval and do it twice once with -ts_exact_final_time stepover and once with exact.

   Barry


I tried increasing the maximum number of rejections and it just takes longer to diverge, and if I set the value to "unlimited" it is basically an infinite loop.

Is there a way to check why is the step rejected? Could the "matchstep" option change tolerances somewhere that would cause that behavior?

Let me know if I should provide more information.

Best,

Sophie Blondel


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