Hi everyone and happy new year, I finally tracked down the issue and it is not related to PETSc: in that specific way of using Xolotl we set the max time to 0 s at the very beginning, so with the matchstep option that sets the dt to 0 s and it diverges.
Thank you for your help, Sophie ________________________________ From: Barry Smith <bsm...@petsc.dev> Sent: Tuesday, December 17, 2024 18:33 To: Blondel, Sophie <sblon...@utk.edu> Cc: Jed Brown <j...@jedbrown.org>; Zhang, Hong <hongzh...@anl.gov>; Emil Constantinescu <emcon...@anl.gov>; petsc-users@mcs.anl.gov <petsc-users@mcs.anl.gov>; xolotl-psi-developm...@lists.sourceforge.net <xolotl-psi-developm...@lists.sourceforge.net> Subject: Re: [petsc-users] "-ts_exact_final_time matchstep" leads to DIVERGED_STEP_REJECTED This output is odd and seems wrong 0 TS dt 0. time 0. This is printing the initial timestep and time before it does any timestepping. We expect dt to be 1e-12 as your other case does print 0 TS dt 1e-12 time 0. What the exact final time flag is set to shouldn't affect the timestep this early in the computation. You could try in the debugger to trace the variable ts->time_step to see when it is being set from 1.e-12 to 0. On Dec 13, 2024, at 4:40 PM, Blondel, Sophie <sblon...@utk.edu> wrote: Barry, The short output is "SNESSolve has not converged due to Nan or Inf norm", the full one is attached. Cheers, Sophie ________________________________ From: Barry Smith <bsm...@petsc.dev<mailto:bsm...@petsc.dev>> Sent: Friday, December 13, 2024 14:56 To: Blondel, Sophie <sblon...@utk.edu<mailto:sblon...@utk.edu>> Cc: Jed Brown <j...@jedbrown.org<mailto:j...@jedbrown.org>>; Zhang, Hong <hongzh...@anl.gov<mailto:hongzh...@anl.gov>>; Emil Constantinescu <emcon...@anl.gov<mailto:emcon...@anl.gov>>; petsc-users@mcs.anl.gov<mailto:petsc-users@mcs.anl.gov> <petsc-users@mcs.anl.gov<mailto:petsc-users@mcs.anl.gov>>; xolotl-psi-developm...@lists.sourceforge.net<mailto:xolotl-psi-developm...@lists.sourceforge.net> <xolotl-psi-developm...@lists.sourceforge.net<mailto:xolotl-psi-developm...@lists.sourceforge.net>> Subject: Re: [petsc-users] "-ts_exact_final_time matchstep" leads to DIVERGED_STEP_REJECTED There is a bit of complicated logic to determine the "adjusted" timestep in TSAdaptChoose() when if (*accept && ts->exact_final_time == TS_EXACTFINALTIME_MATCHSTEP) { Is it possible that hmax = tmax - t; is exactly zero, and the logic below does not correctly handle that case? 0 TS dt 0. time 0. 0 TS dt 0. time 0. 0 TS dt 0. time 0. 0 TS dt 0. time 0. TSAdapt basic step 0 stage rejected (SNES reason DIVERGED_FNORM_NAN) t=0 + 0.000e+00 retrying with dt=0.000e+00 TSAdapt basic step 0 stage rejected (SNES reason DIVERGED_FNORM_NAN) t=0 + 0.000e+00 retrying with dt=0.000e+00 TSAdapt basic step 0 stage rejected (SNES reason DIVERGED_FNORM_NAN) t=0 + 0.000e+00 retrying with dt=0.000e+00 TSAdapt basic step 0 stage rejected (SNES reason DIVERGED_FNORM_NAN) t=0 + 0.000e+00 retrying with dt=0.000e+00 TSAdapt basic step 0 stage rejected (SNES reason DIVERGED_FNORM_NAN) t=0 + 0.000e+00 retrying with dt=0.000e+00 TSAdapt basic step 0 stage rejected (SNES reason DIVERGED_FNORM_NAN) t=0 + 0.000e+00 retrying with dt=0.000e+00 TSAdapt basic step 0 stage rejected (SNES reason DIVERGED_FNORM_NAN) t=0 + 0.000e+00 retrying with dt=0.000e+00 TSAdapt basic step 0 stage rejected (SNES reason DIVERGED_FNORM_NAN) t=0 + 0.000e+00 retrying with dt=0.000e+00 TSAdapt basic step 0 stage rejected (SNES reason DIVERGED_FNORM_NAN) t=0 + 0.000e+00 retrying with dt=0.000e+00 TSAdapt basic step 0 stage rejected (SNES reason DIVERGED_FNORM_NAN) t=0 + 0.000e+00 retrying with dt=0.000e+00 TSAdapt basic step 0 stage rejected (SNES reason DIVERGED_FNORM_NAN) t=0 + 0.000e+00 retrying with dt=0.000e+00 Sophie, Any idea why SNES reason DIVERGED_FNORM_NAN? Could you run with -snes_error_if_not_converged? On Dec 13, 2024, at 2:34 PM, Blondel, Sophie <sblon...@utk.edu<mailto:sblon...@utk.edu>> wrote: 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 <bsm...@petsc.dev<mailto:bsm...@petsc.dev>> Sent: Friday, December 13, 2024 14:21 To: Blondel, Sophie <sblon...@utk.edu<mailto:sblon...@utk.edu>>; Jed Brown <j...@jedbrown.org<mailto:j...@jedbrown.org>>; Zhang, Hong <hongzh...@anl.gov<mailto:hongzh...@anl.gov>>; Emil Constantinescu <emcon...@anl.gov<mailto:emcon...@anl.gov>> Cc: petsc-users@mcs.anl.gov<mailto:petsc-users@mcs.anl.gov> <petsc-users@mcs.anl.gov<mailto:petsc-users@mcs.anl.gov>>; xolotl-psi-developm...@lists.sourceforge.net<mailto:xolotl-psi-developm...@lists.sourceforge.net> <xolotl-psi-developm...@lists.sourceforge.net<mailto:xolotl-psi-developm...@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 <sblon...@utk.edu<mailto:sblon...@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-developm...@lists.sourceforge.net<mailto:xolotl-psi-developm...@lists.sourceforge.net>> Sent: Monday, December 9, 2024 17:29 To: Barry Smith <bsm...@petsc.dev<mailto:bsm...@petsc.dev>> Cc: petsc-users@mcs.anl.gov<mailto:petsc-users@mcs.anl.gov> <petsc-users@mcs.anl.gov<mailto:petsc-users@mcs.anl.gov>>; xolotl-psi-developm...@lists.sourceforge.net<mailto:xolotl-psi-developm...@lists.sourceforge.net> <xolotl-psi-developm...@lists.sourceforge.net<mailto:xolotl-psi-developm...@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 <bsm...@petsc.dev<mailto:bsm...@petsc.dev>> Sent: Monday, December 9, 2024 15:12 To: Blondel, Sophie <sblon...@utk.edu<mailto:sblon...@utk.edu>> Cc: petsc-users@mcs.anl.gov<mailto:petsc-users@mcs.anl.gov> <petsc-users@mcs.anl.gov<mailto:petsc-users@mcs.anl.gov>>; xolotl-psi-developm...@lists.sourceforge.net<mailto:xolotl-psi-developm...@lists.sourceforge.net> <xolotl-psi-developm...@lists.sourceforge.net<mailto:xolotl-psi-developm...@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@mcs.anl.gov<mailto:petsc-users@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 <matchstep_reason.txt>
