SNES Problem

[Barry Smith]

On Wed, 15 Mar 2006, Nils Erik Svangård wrote:

>>
>>    It doesn't like the nonlinear system. If you run on one process with
>> -pc_type lu -snes_monitor what happens? Same problem or does it get
>> past the first timestep? If it fails what if you use a much smaller time
>> step, does it convergen then?
>
> I'll try that when I have access to the code and compiler again,
> however I use -snes_mf because I dont have any jacobian and I seem to
> remember that using -pc_type lu dosent work when using -snes_mf, but I
> might have understood wrong.

   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.

    Barry

> I have used the same timestep I use for the old 3-stage RK I can try a
> really small timestep instead.
> And it fails both when using TS or SNES, which probably almost the
> same thing considering they both try to solve the first timestep.
>
>>>
>>> I have looked at rk.c, and I'm not sure how to use it.
>>> Have I understood correctly that I should: get at copy of rk.c put it
>>> in my working dir, somehow change it so it uses some global variables
>>> or neigboring cellvalues to compute the timestep with the same
>>> algorithm used in the old fortran code, then compile rk.c and make
>>> sure the object file gets linked when compiling my fortran program
>>
>>    Yes,
>>
>
> OK, I will try my best, I have never tried something like that before.
> I rebuild petsc also?)
>
> /nisse
>
>
> --
> Nils-Erik Svangård
> E-Mail: nilserik at gmail.com
> MSN: schweingaard at hotmail.com
> Skype: schweingaard
> Mobil: +46-(0)70-3612178
>
>