[petsc-users] Solution "jumps" after setting timestep

Zhang, Hong hongzhang at anl.gov
Thu Dec 13 11:36:55 CST 2018 

Please make sure your messages go to petsc-users when replying.

On Dec 13, 2018, at 11:25 AM, Moritz.Huck at isea.rwth-aachen.de<mailto:Moritz.Huck at isea.rwth-aachen.de> wrote:

The first solve to 1e-3
    TSAdapt basic arkimex 0:1bee step   0 rejected t=0          + 1.000e-03 dt=1.000e-04  wlte=  102  wltea=   -1 wlter=   -1
    TSAdapt basic arkimex 0:1bee step   0 rejected t=0          + 1.000e-04 dt=1.000e-05  wlte=  127  wltea=   -1 wlter=   -1
    TSAdapt basic arkimex 0:1bee step   0 rejected t=0          + 1.000e-05 dt=1.995e-06  wlte= 5.09  wltea=   -1 wlter=   -1
    TSAdapt basic arkimex 0:1bee step   0 accepted t=0          + 1.995e-06 dt=3.232e-06  wlte=0.309  wltea=   -1 wlter=   -1
    TSAdapt basic arkimex 0:4 step   1 accepted t=1.99488e-06+ 3.232e-06 dt=3.232e-05  wlte=1.65e-06  wltea=   -1 wlter=   -1
    TSAdapt basic arkimex 0:4 step   2 accepted t=5.22663e-06+ 3.232e-05 dt=3.232e-04  wlte=3.96e-05  wltea=   -1 wlter=   -1
    TSAdapt basic arkimex 0:4 step   3 accepted t=3.75441e-05+ 3.232e-04 dt=6.393e-04  wlte=0.000973  wltea=   -1 wlter=   -1
    TSAdapt basic arkimex 0:4 step   4 accepted t=0.000360719+ 6.393e-04 dt=2.962e-03  wlte=0.00142  wltea=   -1 wlter=   -1

the solve steps afterwards:
    TSAdapt basic arkimex 0:4 step   5 accepted t=0.001      + 2.962e-03 dt=7.110e-03  wlte=0.0197  wltea=   -1 wlter=   -1
    TSAdapt basic arkimex 0:4 step   6 accepted t=0.00396151 + 7.110e-03 dt=2.489e-02  wlte=0.00437  wltea=   -1 wlter=   -1
    TSAdapt basic arkimex 0:4 step   7 accepted t=0.0110717  + 2.489e-02 dt=7.079e-02  wlte= 0.01  wltea=   -1 wlter=   -1
    TSAdapt basic arkimex 0:4 step   8 accepted t=0.03596    + 7.079e-02 dt=9.672e-02  wlte=0.188  wltea=   -1 wlter=   -1
    TSAdapt basic arkimex 0:4 step   9 accepted t=0.106753   + 9.672e-02 dt=1.329e-01  wlte=0.184  wltea=   -1 wlter=   -1
around here it reaches a steady state
    TSAdapt basic arkimex 0:4 step  10 accepted t=0.203478   + 1.329e-01 dt=2.432e-01  wlte=0.0586  wltea=   -1 wlter=   -1
    TSAdapt basic arkimex 0:4 step  11 accepted t=0.336424   + 2.432e-01 dt=4.536e-01  wlte=0.0542  wltea=   -1 wlter=   -1
    TSAdapt basic arkimex 0:4 step  12 accepted t=0.579616   + 4.536e-01 dt=1.112e+00  wlte=0.0182  wltea=   -1 wlter=   -1
    TSAdapt basic arkimex 0:4 step  13 accepted t=1.03324    + 9.668e-01 dt=3.286e+00  wlte=0.00492  wltea=   -1 wlter=   -1

here I set the timestep to 1e-3 artificially and the solution deviates from the steady state solution

The TS time jumps between step 13 and step 14, which is probably the cause of the jump in the solution.
Did you reset the time to t=2 by calling TSSetTime() after step 13?

Hong

      TSAdapt basic arkimex 0:4 step  14 accepted t=2          + 1.000e-03 dt=3.845e-03  wlte=0.003  wltea=   -1 wlter=   -1
      TSAdapt basic arkimex 0:4 step  15 accepted t=2.001      + 3.845e-03 dt=3.845e-02  wlte=6.95e-06  wltea=   -1 wlter=   -1
      TSAdapt basic arkimex 0:4 step  16 accepted t=2.00485    + 3.845e-02 dt=3.845e-01  wlte=4.31e-05  wltea=   -1 wlter=   -1
      TSAdapt basic arkimex 0:4 step  17 accepted t=2.0433     + 3.845e-01 dt=2.473e+00  wlte=0.000384  wltea=   -1 wlter=   -1
      TSAdapt basic arkimex 0:4 step  18 accepted t=2.42784    + 2.473e+00 dt=4.540e+00  wlte=0.0578  wltea=   -1 wlter=   -1
this point is "back on track"
      TSAdapt basic arkimex 0:4 step  19 accepted t=4.90058    + 4.540e+00 dt=4.649e+00  wlte=0.596  wltea=   -1 wlter=   -1

Von: Zhang, Hong <hongzhang at anl.gov<mailto:hongzhang at anl.gov>>
Gesendet: Donnerstag, 13. Dezember 2018 17:39
An: Huck, Moritz <Moritz.Huck at isea.rwth-aachen.de<mailto:Moritz.Huck at isea.rwth-aachen.de>>
Cc: petsc-users at mcs.anl.gov<mailto:petsc-users at mcs.anl.gov>
Betreff: Re: [petsc-users] Solution "jumps" after setting timestep

Can you show the outputs of -ts_monitor for both cases (one with oscillations and one without)?

Thanks,
Hong


On Dec 13, 2018, at 9:48 AM, Moritz.Huck at isea.rwth-aachen.de<mailto:Moritz.Huck at isea.rwth-aachen.de> wrote:

Hi,
Sure after reaching a steady state it looks like this:
    0 SNES Function norm 3.767377637168e-03
    1 SNES Function norm 2.529971638368e-05
    2 SNES Function norm 4.433873358247e-09
    3 SNES Function norm 4.535675922104e-11
    0 SNES Function norm 9.898938706929e-04
    1 SNES Function norm 1.322473621975e-05
    2 SNES Function norm 1.672724799379e-09
    3 SNES Function norm 1.338501638801e-11
    0 SNES Function norm 1.624500221071e-03
    1 SNES Function norm 2.448515345247e-05
    2 SNES Function norm 6.225549426481e-09
    3 SNES Function norm 1.062516222150e-10
    4 SNES Function norm 6.493758120241e-13
    0 SNES Function norm 1.106311709708e-03
    1 SNES Function norm 2.475673243430e-05
    2 SNES Function norm 9.969586735411e-09
    3 SNES Function norm 2.479591395229e-10
    4 SNES Function norm 1.542689576708e-12
    0 SNES Function norm 6.070943996748e-04
    1 SNES Function norm 1.648134285171e-05
    2 SNES Function norm 8.461078655420e-09
    3 SNES Function norm 2.480863447790e-10
    4 SNES Function norm 1.513977618851e-12
      TSAdapt basic arkimex 0:4 step  15 accepted t=5.67201    + 4.328e+00 dt=4.687e+00  wlte$
0.477  wltea=   -1 wlter=   -1

If I set the next target time (in tssolve) to be tlast+1e-3 it looks like this:
    0 SNES Function norm 4.734802409365e-03
    1 SNES Function norm 6.173939866359e-13
    0 SNES Function norm 5.633294284900e-04
    1 SNES Function norm 3.575533754564e-13
    0 SNES Function norm 9.651618110271e-04
    1 SNES Function norm 6.863177319359e-13
    0 SNES Function norm 7.706102281617e-04
    1 SNES Function norm 8.490865565002e-13
    0 SNES Function norm 5.028108294534e-04
    1 SNES Function norm 6.905750968862e-13
      TSAdapt basic arkimex 0:4 step  16 accepted t=10         + 1.000e-03 dt=2.612e-03  wlte$
0.0141  wltea=   -1 wlter=   -1

The SNES solver has a atoll of 1e-10, setting the atoll to lower values does not change the result.

Thank you,
Moritz

Von: Zhang, Hong <hongzhang at anl.gov<mailto:hongzhang at anl.gov>>
Gesendet: Donnerstag, 13. Dezember 2018 16:42
An: Huck, Moritz <Moritz.Huck at isea.rwth-aachen.de<mailto:Moritz.Huck at isea.rwth-aachen.de>>
Cc: petsc-users at mcs.anl.gov<mailto:petsc-users at mcs.anl.gov>
Betreff: Re: [petsc-users] Solution "jumps" after setting timestep

Can you please add command line options -ts_monitor -snes_monitor and show us the outputs?

Thanks,
Hong (Mr.)



On Nov 4, 2018, at 6:19 AM, Moritz.Huck--- via petsc-users <petsc-users at mcs.anl.gov<mailto:petsc-users at mcs.anl.gov>> wrote:

Hi,

I using the basic adaptor.
If I let the adaptor handle everything it does not oscillates.
I don’t mean setting the timestep at the start (which does not produces the
problem),
I need to set during runtime between two steps.

Best Regards,

Moritz

-----Ursprüngliche Nachricht-----
Von: Constantinescu, Emil M. <emconsta at anl.gov<mailto:emconsta at anl.gov>>
Gesendet: Samstag, 3. November 2018 15:43
An: Huck, Moritz <Moritz.Huck at isea.rwth-aachen.de<mailto:Moritz.Huck at isea.rwth-aachen.de>>; petsc-users at mcs.anl.gov<mailto:petsc-users at mcs.anl.gov>
Betreff: Re: [petsc-users] Solution "jumps" after setting timestep

On 11/3/18 4:56 AM, Moritz.Huck--- via petsc-users wrote:


Hi,

I am using the IMEX Runge Kutta to solve an implicit DAE (G=0).

When I manually set the time step (TSSetTimestep) my solution jumps.

When you don't set the time step, does it still oscillates? If not, can you
check if it oscillates when reducing the fixed initial time step?
Did you turn the adaptivity off (-ts_adapt_type none)?

Emil




If I go from  a steady state to the  same state, it oscillates a few
time and comes back to the steady solution.

Can this be prevented?

Thank you,

Moritz

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