SNES Problem

[Nils Erik Svangård]

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