[petsc-users] Any suggestion for this kinds of matrix?

[Matthew Knepley]

On Thu, Nov 10, 2011 at 1:48 PM, Bao Kai <paeanball at gmail.com> wrote:

> Dear all,
>
> I have been trying with PETSC to solve the linear system from mixed finite
> element method.
>
> The pattern of the matrix is as the following, but due to the irregular
> boundary involved, the matrix A is not strictly symmetric.
>
>    A     dt* C
>
>    C^T     0
>
>  As a  result of the matrix pattern, the diagonal entries of the
> bottom-right portion are all zero.
>
> I am just wondering if there are any suggestion of the type of the solver
> and preconditioner for this kinds of linear system?  Thank you very much.
>
> When I tried to solve the system with PETSC, I got the following
> information. (  PCType PCASM,  KSPType, KSPFGMRES )
>

ILU is jsut not going to work for this type of matrix (a saddle point). I
suggest reading about PCFIELDSPLIT.

   Matt


> [0]PETSC ERROR: --------------------- Error Message
> ------------------------------------
> [0]PETSC ERROR: Object is in wrong state!
> [0]PETSC ERROR: Matrix is missing diagonal entry 288398!
> [0]PETSC ERROR:
> ------------------------------------------------------------------------
> [0]PETSC ERROR: Petsc Release Version 3.2.0, Patch 4, Sun Oct 23 12:23:18
> CDT 2011
> [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: Libraries linked from
> /home/baok/software/petsc-3.2-p4/arch-linux2-c-debug-withhypre/lib
> [0]PETSC ERROR: Configure run at Thu Nov 10 11:49:03 2011
> [0]PETSC ERROR: Configure options --download-hypre=yes
> [0]PETSC ERROR:
> ------------------------------------------------------------------------
> [0]PETSC ERROR: MatILUFactorSymbolic_SeqAIJ_ilu0() line 1636 in
> /home/baok/software/petsc-3.2-p4/src/mat/impls/aij/seq/aijfact.c
> [0]PETSC ERROR: MatILUFactorSymbolic_SeqAIJ() line 1740 in
> /home/baok/software/petsc-3.2-p4/src/mat/impls/aij/seq/aijfact.c
> [0]PETSC ERROR: MatILUFactorSymbolic() line 6092 in
> /home/baok/software/petsc-3.2-p4/src/mat/interface/matrix.c
> [0]PETSC ERROR: PCSetUp_ILU() line 216 in
> /home/baok/software/petsc-3.2-p4/src/ksp/pc/impls/factor/ilu/ilu.c
> [0]PETSC ERROR: PCSetUp() line 819 in
> /home/baok/software/petsc-3.2-p4/src/ksp/pc/interface/precon.c
> [0]PETSC ERROR: KSPSetUp() line 260 in
> /home/baok/software/petsc-3.2-p4/src/ksp/ksp/interface/itfunc.c
> [0]PETSC ERROR: PCSetUpOnBlocks_ASM() line 339 in
> /home/baok/software/petsc-3.2-p4/src/ksp/pc/impls/asm/asm.c
> [0]PETSC ERROR: PCSetUpOnBlocks() line 852 in
> /home/baok/software/petsc-3.2-p4/src/ksp/pc/interface/precon.c
> [0]PETSC ERROR: KSPSetUpOnBlocks() line 154 in
> /home/baok/software/petsc-3.2-p4/src/ksp/ksp/interface/itfunc.c
> [0]PETSC ERROR: KSPSolve() line 380 in
> /home/baok/software/petsc-3.2-p4/src/ksp/ksp/interface/itfunc.c
> [0]PETSC ERROR: main() line 261 in src/ksp/ksp/examples/tutorials/ex78.c
>
>
> Best Regards,
> Kai
>
>


-- 
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
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.mcs.anl.gov/pipermail/petsc-users/attachments/20111110/2ea2b385/attachment-0001.htm>