[petsc-users] puzzling arkimex logic

[Jed Brown]

This default probably shouldn't be zero, and probably lengthening steps should be more gentle after a recent failure. But Mark, please let us know if what's there works for you.

"Zhang, Hong via petsc-users" <petsc-users at mcs.anl.gov> writes:

> Hi Mark,
>
> You might want to try -ts_adapt_time_step_increase_delay to delay increasing the time step after it has been decreased due to a failed solve.
>
> Hong (Mr.)
>
>> On Jan 2, 2023, at 12:17 PM, Mark Adams <mfadams at lbl.gov> wrote:
>> 
>> I am using arkimex and the logic with a failed KSP solve is puzzling. This step starts with a dt of ~.005, the linear solver fails and cuts the time step by 1/4. So far, so good. The step then works but the next time step the time step goes to ~0.006.
>> TS seems to have forgotten that it had to cut the time step back.
>> Perhaps that logic is missing or my parameters need work?
>> 
>> Thanks,
>> Mark
>> 
>> -ts_adapt_dt_max 0.01 # (source: command line)
>> -ts_adapt_monitor # (source: file)
>> -ts_arkimex_type 1bee # (source: file)
>> -ts_dt .001 # (source: command line)
>> -ts_max_reject 10 # (source: file)
>> -ts_max_snes_failures -1 # (source: file)
>> -ts_max_steps 8000 # (source: command line)
>> -ts_max_time 14 # (source: command line)
>> -ts_monitor # (source: file)
>> -ts_rtol 1e-6 # (source: command line)
>> -ts_type arkimex # (source: file)
>> 
>>   Nonlinear solve converged due to CONVERGED_SNORM_RELATIVE iterations 2
>>       TSAdapt basic arkimex 0:1bee step   1 accepted t=0.001      + 2.497e-03 dt=5.404e-03  wlte=0.173  wltea=   -1 wlter=  
>>  -1
>> 2 TS dt 0.00540401 time 0.00349731
>>     0 SNES Function norm 1.358886930084e-05 
>>     Linear solve did not converge due to DIVERGED_ITS iterations 100
>>   Nonlinear solve did not converge due to DIVERGED_LINEAR_SOLVE iterations 0
>>       TSAdapt basic step   2 stage rejected (DIVERGED_LINEAR_SOLVE) t=0.00349731 + 5.404e-03 retrying with dt=1.351e-03 
>>     0 SNES Function norm 1.358886930084e-05 
>>     Linear solve converged due to CONVERGED_RTOL iterations 19
>>     1 SNES Function norm 4.412110425362e-10 
>>     Linear solve converged due to CONVERGED_RTOL iterations 6
>>     2 SNES Function norm 4.978968053066e-13 
>>   Nonlinear solve converged due to CONVERGED_SNORM_RELATIVE iterations 2
>>     0 SNES Function norm 8.549322067920e-06 
>>     Linear solve converged due to CONVERGED_RTOL iterations 14
>>     1 SNES Function norm 8.357075378456e-11 
>>     Linear solve converged due to CONVERGED_RTOL iterations 4
>>     2 SNES Function norm 4.983138402512e-13 
>>   Nonlinear solve converged due to CONVERGED_SNORM_RELATIVE iterations 2
>>     0 SNES Function norm 1.044832467924e-05 
>>     Linear solve converged due to CONVERGED_RTOL iterations 13
>>     1 SNES Function norm 1.036101875301e-10 
>>     Linear solve converged due to CONVERGED_RTOL iterations 4
>>     2 SNES Function norm 4.984888077288e-13 
>>   Nonlinear solve converged due to CONVERGED_SNORM_RELATIVE iterations 2
>>       TSAdapt basic arkimex 0:1bee step   2 accepted t=0.00349731 + 1.351e-03 dt=6.305e-03  wlte=0.0372  wltea=   -1 wlter= 
>>   -1
>> 3 TS dt 0.00630456 time 0.00484832
>>     0 SNES Function norm 8.116559104264e-06 
>>     Linear solve did not converge due to DIVERGED_ITS iterations 100