Ryan Yan vyan2000 at gmail.com
Fri May 15 12:20:49 CDT 2009

```Hi all,
I am tring to use the tfs preconditioner to solve a large sparse mpiaij
matrix.

11111111111111111111111111111111111111111
It works very well with a small matrix 45*45(Actually a 9*9 block matrix
with blocksize 5) on 2 processors; Out put is as follows:

0 KSP preconditioned resid norm 3.014544557924e+04 true resid norm
2.219812091849e+04 ||Ae||/||Ax|| 1.000000000000e+00
1 KSP preconditioned resid norm 3.679021546908e-03 true resid norm
1.502747104104e-03 ||Ae||/||Ax|| 6.769704109737e-08
2 KSP preconditioned resid norm 2.331909907779e-09 true resid norm
8.737892755044e-10 ||Ae||/||Ax|| 3.936320910733e-14
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: tfs
linear system matrix = precond matrix:
Matrix Object:
type=mpiaij, rows=45, cols=45
total: nonzeros=825, allocated nonzeros=1350
using I-node (on process 0) routines: found 5 nodes, limit used is 5
Norm of error 2.33234e-09, Iterations 2

2222222222222222222222222222222222222222

However, when I use the same code for a larger sparse matrix, a 18656 *
18656 block matrix with blocksize 5); it encounters the followins
error.(Same error message for using 1 and 2 processors, seperately)

[0]PETSC ERROR:
------------------------------------------------------------------------
[0]PETSC ERROR: Caught signal number 11 SEGV: Segmentation Violation,
probably memory access out of range
[0]PETSC ERROR: Try option -start_in_debugger or -on_error_attach_debugger
[0]PETSC ERROR: or see
http://www.mcs.anl.gov/petsc/petsc-as/documentation/troubleshooting.html#Signal[0]PETSCERROR:
or try
http://valgrind.org on linux or man libgmalloc on Apple to find memory
corruption errors
[0]PETSC ERROR: likely location of problem given in stack below
[0]PETSC ERROR: ---------------------  Stack Frames
------------------------------------
[0]PETSC ERROR: Note: The EXACT line numbers in the stack are not available,
[0]PETSC ERROR:       INSTEAD the line number of the start of the function
[0]PETSC ERROR:       is given.
[0]PETSC ERROR: [0] PCSetUp_TFS line 116 src/ksp/pc/impls/tfs/tfs.c
[0]PETSC ERROR: [0] PCSetUp line 764 src/ksp/pc/interface/precon.c
[0]PETSC ERROR: [0] KSPSetUp line 183 src/ksp/ksp/interface/itfunc.c
[0]PETSC ERROR: [0] KSPSolve line 305 src/ksp/ksp/interface/itfunc.c
[0]PETSC ERROR: --------------------- Error Message
------------------------------------
[0]PETSC ERROR:
------------------------------------------------------------------------
[0]PETSC ERROR: Petsc Release Version 2.3.3, Patch 15, Tue Sep 23 10:02:49
CDT 2008 HG revision: 31306062cd1a6f6a2496fccb4878f485c9b91760
[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: ./kspex1reader_binmpiaij on a linux-gnu named vyan2000-linux
by vyan2000 Fri May 15 01:06:12 2009
/home/vyan2000/local/PPETSc/petsc-2.3.3-p15//lib/linux-gnu-c-debug
[0]PETSC ERROR: Configure run at Mon May  4 00:59:41 2009
[0]PETSC ERROR: Configure options
--with-mpi-dir=/home/vyan2000/local/mpich2-1.0.8p1/ --with-debugger=gdb
[0]PETSC ERROR:
------------------------------------------------------------------------
[0]PETSC ERROR: User provided function() line 0 in unknown directory unknown
file
application called MPI_Abort(MPI_COMM_WORLD, 59) - process 0[cli_0]:
aborting job:
application called MPI_Abort(MPI_COMM_WORLD, 59) - process 0

3333333333333333333333333333333333333333333333

I have the exact solution x in hands, so before I push the matrix into the
ksp solver, I did check the PETSC loaded matrix A and rhs vector b, by
verifying Ax-b=0,  in  both cases of 1 processor and 2 processors.

Any sugeestions?

Thank you very much,

Yan
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