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

[Blondel, Sophie]

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>
Sent: Monday, December 9, 2024 15:12
To: Blondel, Sophie <sblondel at utk.edu>
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



On Dec 9, 2024, at 2:56 PM, Blondel, Sophie via petsc-users <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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