problem with -snes_mf_operator option

[Vijay S. Mahadevan]

Matt,

Yes, I tested ex5 and it works correctly. But I am not suggesting any
errors in PETSc code here. I am kind of puzzled that my unchanged code
calling PETSc's SNESSolve works while using -snes_mf option (no
allocation for Jac or Prec) and with no option (allocation for both
Jac and Prec). And since -snes_mf_operator exists in between,  (no
allocation for Jac but allocate Prec), atleast in philosophy, I
expected it to work without any faults. This is also the reason why I
set the Prec = Identity rather than the true Jacobian to eliminate
user errors.

Anyway I still have not figured out why the NULL reference occurs when
PETSc allocates MFFD object in my current code. I was just looking for
suggestions here to help me find the error.

Vijay

On Wed, Mar 26, 2008 at 6:01 PM, Matthew Knepley <knepley at gmail.com> wrote:
> I am not sure what is going on with your code, but I have just tested an example
>  and it works. I recommend you try
>
>   cd src/snes/examples/tutorials
>   make ex5
>   ./ex5 -snes_monitor -snes_view
>   ./ex5 -snes_monitor -snes_view -snes_mf
>   ./ex5 -snes_monitor -snes_view -snes_mf_operator
>
>   Thanks,
>
>      Matt
>
>
>
>  On Wed, Mar 26, 2008 at 4:14 PM, Vijay S. Mahadevan <vijay.m at gmail.com> wrote:
>  > Hi all,
>  >
>  >  I have a nonlinear solver test code that can use a user specified
>  >  Jacobian function directly, set using SNESSetJacobian. Now if I use
>  >  -snes_mf option, the solution scheme depends only on the residual and
>  >  the convergence is equivalent to the case when using the real Jacobian
>  >  matrix itself. But if I try the -snes_mf_operator option, with the
>  >  Jacobian=NULL to start with and the preconditioner being correctly
>  >  allocated the memory needed, I end up with a NULL argument exception.
>  >  I also alternately set the preconditioner to Identity matrix in order
>  >  to avoid any problems from user code to trickling in, but to no avail.
>  >
>  >  Here's the call stack.
>  >
>  >  [0]PETSC ERROR: Null argument, when expecting valid pointer!
>  >  [0]PETSC ERROR: Null Object: Parameter # 1!
>  >  [0]PETSC ERROR:
>  >  ------------------------------------------------------------------------
>  >  [0]PETSC ERROR: Petsc Release Version 2.3.3, Patch 7, Fri Oct 26
>  >  14:21:35 CDT 2007 HG revision:
>  >  2e223033ba960114833e1f9713ab393ec78c056f
>  >  [0]PETSC ERROR: See docs/changes/index.html for recent updates.
>  >  [0]PETSC ERROR: See docs/faq.html for hints about trouble shooting.
>  >  [0]PETSC ERROR: See docs/index.html for manual pages.
>  >  [0]PETSC ERROR:
>  >  ------------------------------------------------------------------------
>  >  [0]PETSC ERROR: bin/test-dbg on a linux-gnu named grove by vijaysm Wed
>  >  Mar 26 16:06:45 2008
>  >  [0]PETSC ERROR: Libraries linked from
>  >  /state/partition1/local/petsc-2.3.3-p7/lib/linux-gnu-c-debug
>  >  [0]PETSC ERROR: Configure run at Fri Nov  9 15:02:46 2007
>  >  [0]PETSC ERROR: Configure options --with-cc=gcc --with-fc=ifort
>  >  --with-cxx=g++ --download-f-blas-lapack=1 --download-mpich=1
>  >  --with-shared=1
>  >  [0]PETSC ERROR:
>  >  ------------------------------------------------------------------------
>  >  [0]PETSC ERROR: PetscObjectGetComm() line 34 in src/sys/objects/gcomm.c
>  >  [0]PETSC ERROR: VecNormBegin() line 495 in src/vec/vec/utils/comb.c
>  >  [0]PETSC ERROR: MatMFFDCompute_WP() line 73 in src/mat/impls/mffd/wp.c
>  >  [0]PETSC ERROR: MatMult_MFFD() line 294 in src/mat/impls/mffd/mffd.c
>  >  [0]PETSC ERROR: MatMult() line 1632 in src/mat/interface/matrix.c
>  >  [0]PETSC ERROR: PCApplyBAorAB() line 584 in src/ksp/pc/interface/precon.c
>  >  [0]PETSC ERROR: GMREScycle() line 159 in src/ksp/ksp/impls/gmres/gmres.c
>  >  [0]PETSC ERROR: KSPSolve_GMRES() line 241 in src/ksp/ksp/impls/gmres/gmres.c
>  >  [0]PETSC ERROR: KSPSolve() line 379 in src/ksp/ksp/interface/itfunc.c
>  >  [0]PETSC ERROR: SNES_KSPSolve() line 2578 in src/snes/interface/snes.c
>  >  [0]PETSC ERROR: SNESSolve_LS() line 184 in src/snes/impls/ls/ls.c
>  >  [0]PETSC ERROR: SNESSolve() line 1871 in src/snes/interface/snes.c
>  >
>  >  From what I can understand from the PETSc code (snes.c, mffd.c), the
>  >  current_u for MFFD context is NULL here. And that is the reason for
>  >  the final exception. But I do not understand how this can be since it
>  >  works perfectly fine with -snes_mf option with no changes in the code.
>  >
>  >  Please do let me know if you think I should specifically be looking
>  >  for something to tackle this issue. Any help will be appreciated.
>  >
>  >  Thanks,
>  >  Vijay
>  >
>  >
>
>
>
>  --
>  What most experimenters take for granted before they begin their
>  experiments is infinitely more interesting than any results to which
>  their experiments lead.
>  -- Norbert Wiener
>
>