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 > >
