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

Moritz.Huck at isea.rwth-aachen.de Moritz.Huck at isea.rwth-aachen.de
Fri Dec 14 10:28:06 CST 2018


Hello, 
thank you  this seems to be a reasonable explanation.
I will try this for my "steady" phases.
I have also phases where my Neumann boundary conditions change with time (in my real application, here I uses constant conditions), in this time I also need the results at exact time points.
Can I get these without setting explicit end times?

Best Regards,
Moritz


-----Ursprüngliche Nachricht-----
Von: Zhang, Hong <hongzhang at anl.gov> 
Gesendet: Freitag, 14. Dezember 2018 17:13
An: Huck, Moritz <Moritz.Huck at isea.rwth-aachen.de>
Cc: petsc-users <petsc-users at mcs.anl.gov>
Betreff: Re: [petsc-users] Solution "jumps" after setting timestep



> On Dec 14, 2018, at 5:16 AM, Moritz.Huck at isea.rwth-aachen.de wrote:
> 
> Correction.
> Not exactly more like this
> While t<2
> 	t=TSGetTime
> 	h=TSGetTimeStep
> 	TSSetMaxTime(min(t+h,2)
> 	TSSolve
> t=TSGetTime
> TSSetMaxTime(t+1e-3)
> TSSolve
> While t<10
> 	t=TSGetTime
> 	h=TSGetTimeStep
> 	TSSetMaxTime(min(t+h,10)
> 	TSSolve
> 
> @Hong
> No did not reset the time. Shouldn’t the time  already 2 in this case?

My mistake. The time looks fine. Now I understand what your code does.

You might want to use TSSetTimeStep() to change the step size and there is no need to have loops. You can define a TSPostStep function and call TSSolve() just once. When solving a DAE, each call to TSSolve() would trigger a restart step internally to calculate an initial slope for the DAE. I suspect that the jump was caused by these restart steps.

Hong  

> -----Ursprüngliche Nachricht-----
> Von: petsc-users <petsc-users-bounces at mcs.anl.gov> Im Auftrag von 
> Moritz.Huck--- via petsc-users
> Gesendet: Freitag, 14. Dezember 2018 12:06
> An: Emil Constantinescu <emconsta at mcs.anl.gov>; Zhang, Hong 
> <hongzhang at anl.gov>
> Cc: petsc-users <petsc-users at mcs.anl.gov>
> Betreff: Re: [petsc-users] Solution "jumps" after setting timestep
> 
> In this example yes.
> 
> -----Ursprüngliche Nachricht-----
> Von: Emil Constantinescu <emconsta at mcs.anl.gov>
> Gesendet: Donnerstag, 13. Dezember 2018 20:21
> An: Zhang, Hong <hongzhang at anl.gov>; Huck, Moritz 
> <Moritz.Huck at isea.rwth-aachen.de>
> Cc: petsc-users <petsc-users at mcs.anl.gov>
> Betreff: Re: [petsc-users] Solution "jumps" after setting timestep
> 
> Okay, so you start your integration with "TSSetMaxTime and then call TSSolve (TSSetExactFinalTime is set to TS_EXACTFINALTIME_MATCHSTEP)"
> 
> Then after it's done at t=2 you tell TS that TSSetTimeStep(ts,1e-3) and call TSSolve again?
> 
> Emil
> 
> 
> 
> On 12/13/18 11:36 AM, Zhang, Hong via petsc-users wrote:
>> 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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