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Re: SNES Problem


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
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