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

Thu Dec 13 09:48:51 CST 2018

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> 
Gesendet: Donnerstag, 13. Dezember 2018 16:42
An: Huck, Moritz <Moritz.Huck at isea.rwth-aachen.de>
Cc: 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. < <mailto:emconsta at anl.gov> emconsta at anl.gov> 
Gesendet: Samstag, 3. November 2018 15:43
An: Huck, Moritz < <mailto:Moritz.Huck at isea.rwth-aachen.de> Moritz.Huck at isea.rwth-aachen.de>;  <mailto:petsc-users at mcs.anl.gov> 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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