SNES Problem

[Barry Smith]

   Based on my understanding. This is correct.

   Suggest you run a TINY problem with your "old" code
and the TS (and or SNES one). Print out everything. The
current solution the result from calling Get_DRO() and
compare the runs, when and why do they change? This will
help understand what is going on.

    Barry


On Fri, 17 Mar 2006, Nils Erik Svangård wrote:

> Ok, I managed to compile and link rk.c to my fortran program, I forgot
> that in C you need a ;  in the end of every statement. (stupid mistake
> ;) )
>
> I have just added one line to see if it works.
>
>  /* computing new dt */
>     dt = dt * dt_fac;
>
>     /* Start Nisse stuff */
>        ierr = PetscPrintf(PETSC_COMM_WORLD,"Nisse prints dt: %f\n",dt);
>     /* End nisse stuff */
>
>
>     if(ts->ptime+dt > ts->max_time){
>        dt = ts->max_time - ts->ptime;
>     }
>
> I just try to print the current timestep, however this is never
> printed. And I'm not really sure that it is the timestep that is
> causing the problems.
>
> I have used call TSGetTimeStep(ts,timestep,ierr) to monitor what
> timestep TS uses and it seem ok. However after the first iteration of
> FormFunction everything seems ok, but in start of the second iteration
> all values are really strange.
>
> I see the same thing when using SNES and my back euler implementation,
> it iterate many more times however, but all of a sudden the all "in"
> values are in the range 0.2-0.7 (for all 7 equations) and my code
> bombs because of the strange values.
>
> When using TS and  running with  -snes_mf -ts_type beuler -ksp_rtol
> 1.e-10 this is what printed just before producing strange values:
> KSP Object:
>  type: gmres
>    GMRES: restart=30, using Classical (unmodified) Gram-Schmidt
> Orthogonalization with no iterative refinement
>    GMRES: happy breakdown tolerance 1e-30
>  maximum iterations=10000, initial guess is zero
>  tolerances:  relative=1e-10, absolute=1e-50, divergence=10000
>  left preconditioning
> PC Object:
>  type: none
>  linear system matrix = precond matrix:
>  Matrix Object:
>    type=mffd, rows=70000, cols=70000
>        SNES matrix-free approximation:
>          err=1e-07 (relative error in function evaluation)
>          Using wp compute h routine
>          Computes normA
>
>
> And just to make sure that I havent misunderstood how SNES and TS work:
> If the original 3-stage RK uses (my numbering):
> 1.  RO0(L)=RO(L)
>     Get_DRO(RO(L))
>     RO(L)=RO0(L)+CFL*DRO(L)
> 2.  RO0(L)=.5*(RO0(L)+RO(L))
>     Get_DRO(RO(L))
>     RO(L)=RO0(L)+.5*CFL*DRO(L)
> 3.  Get_DRO(RO(L))
>     RO(L)=RO0(L)+.5*CFL*DRO(L)
>
> Then this should be in TS which should return du/dt which is DRO:
>      RO(L)=xx(1,L)
>      Get_DRO(RO(L))
>      ff(1,L) = DRO(L)
>
> And in SNES with back euler:
>      (Old RO from previous iteration ORO(L)
>      RO(L)=xx(1,L)
>      Get_DRO(RO(L))
>      ff(1,L)= RO(L)-OLD(1,L)-TSF(L)*DRO(L)
>
>
> This became a long mail, I hope this shows if I missed something vital.
> /nisse
> On 3/16/06, Nils Erik Svangård <nilserik at gmail.com> wrote:
>> Barry,
>> the problem is making the objectfile, but I'll try again when I have
>> the code. I will check the makefile for the c-examples.
>> /nisse
>>
>> On 3/16/06, Barry Smith <bsmith at mcs.anl.gov> wrote:
>>>
>>>    Nisse,
>>>
>>>      Just list it in your makefile with all your other object
>>> files (that come from Fortran). Send the output if this fails.
>>>
>>>     Barry
>>>
>>>
>>> On Thu, 16 Mar 2006, Nils Erik Svangård wrote:
>>>
>>>> I havent managed to get rk.c compiled with changes. how do I compile
>>>> it in my working directory to get a object file. I just realised that
>>>> I probably forgot to link it against $TSLIB but should I need to that
>>>> when I dont do any linking, the linking is done when linking the
>>>> fortran and the c code?
>>>> Or what am I doing wrong (I not that good with C++ and linking).
>>>> /nisse
>>>>
>>>> On 3/15/06, Barry Smith <bsmith at mcs.anl.gov> wrote:
>>>>>
>>>>>    Both
>>>>>
>>>>>
>>>>> On Wed, 15 Mar 2006, Nils Erik Svangård wrote:
>>>>>
>>>>>>>
>>>>>>>    Sorry, I forgot. Is the linear solver converging? If not, then that
>>>>>>> is the problem? Use a tolerance like -ksp_rtol 1.e-10 and see if the
>>>>>>> nonlinear solver converges.
>>>>>>>
>>>>>>
>>>>>> I'll try that when I have access to the code. I havent checked if the
>>>>>> linear solver converges is thera a -kspmonitor or -kspconvergedreason
>>>>>> I should use?
>>>>>>
>>>>>> /nisse
>>>>>>
>>>>>>
>>>>>
>>>>
>>>>
>>>> --
>>>> Nils-Erik Svangård
>>>> E-Mail: nilserik at gmail.com
>>>> MSN: schweingaard at hotmail.com
>>>> Skype: schweingaard
>>>> Mobil: +46-(0)70-3612178
>>>>
>>>>
>>>
>>
>>
>> --
>> Nils-Erik Svangård
>> E-Mail: nilserik at gmail.com
>> MSN: schweingaard at hotmail.com
>> Skype: schweingaard
>> Mobil: +46-(0)70-3612178
>>
>
>
> --
> Nils-Erik Svangård
> E-Mail: nilserik at gmail.com
> MSN: schweingaard at hotmail.com
> Skype: schweingaard
> Mobil: +46-(0)70-3612178
>
>