[CIG-SHORT] PyLith problems

[Brad Aagaard]

Jiangning-

The zero pivot suggests that you have a singular matrix. This usually means 
that the problem is not sufficiently constrained (some sort of rigid body 
motion is allowed). This is what why the asm preconditioner doesn't work for 
the two-cell examples. I think it would also show up if you have cells that 
are not associated with any material (i.e., the ids don't match), so that the 
stiffness matrix contains a bug of zeros.

Brad


On Thursday 06 December 2007, Jiangning Lu wrote:
> Hi,
>
> When I tried to run one of my model by setting pc_type = asm, I got the
> following error:
> ......
>  -- Solving linear equations.
> [0]PETSC ERROR: --------------------- Error Message -------------
> [0]PETSC ERROR: Detected zero pivot in LU factorization
> see
> http://www.mcs.anl.gov/petsc/petsc-as/documentation/troubleshooting.html#Ze
>roPivot! [0]PETSC ERROR: Zero pivot row 61695 value 2.29519e-19 tolerance
> 2.93442e-13 * rowsum 0.293442!
> [0]PETSC ERROR: Petsc Development Version 2.3.3, Patch 8, unknown HG
> revision: unknown
> [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:
> /chandler/home/jlu/scratch1/pylith_workarea/nemesis/trunk/mpinemesis on a
> linux-gnu named elsasser by jlu Thu Dec  6 12:50:16 2007
> [0]PETSC ERROR: Libraries linked from
> /chandler/home/jlu/scratch1/pylith_workarea/petsc-dev/lib
> [0]PETSC ERROR: Configure run at Wed Nov 28 15:24:59 2007
> [0]PETSC ERROR: Configure options --with-sieve=1 --with-clanguage=C++
> --with-shared=1 --download-f-blas-lapack=1 --with-boost=1
> --download-boost=1 --with-chaco=1 --download-chaco=1 --with-mpi=1
> --download-mpich=1
> --with-mpi-shared=1
> [0]PETSC ERROR:
> ------------------------------------------------------------------------
> [0]PETSC ERROR: MatLUFactorNumeric_Inode() line 1495 in
> src/mat/impls/aij/seq/inode.c
> [0]PETSC ERROR: MatLUFactorNumeric() line 2276 in
> src/mat/interface/matrix.c [0]PETSC ERROR: PCSetUp_ILU() line 564 in
> src/ksp/pc/impls/factor/ilu/ilu.c [0]PETSC ERROR: PCSetUp() line 788 in
> src/ksp/pc/interface/precon.c [0]PETSC ERROR: KSPSetUp() line 234 in
> src/ksp/ksp/interface/itfunc.c [0]PETSC ERROR: PCSetUpOnBlocks_ASM() line
> 224 in src/ksp/pc/impls/asm/asm.c [0]PETSC ERROR: PCSetUpOnBlocks() line
> 821 in src/ksp/pc/interface/precon.c [0]PETSC ERROR: KSPSetUpOnBlocks()
> line 158 in src/ksp/ksp/interface/itfunc.c [0]PETSC ERROR: KSPSolve() line
> 347 in src/ksp/ksp/interface/itfunc.c [0]PETSC ERROR: preallocateOperator()
> line 190 in
> unknowndirectory/solver_embed.cpp
>
> When I changed the setting to pc_type = jacobi, the error did not show up,
> but the result looks not right either.
> Any thoughts?
>
> Thanks!!
> Jiangning
>
> ---
> Jiangning Lü
> 54-521     x3-6389
> Geophysics
> EAPS, MIT
> johnnylu at mit.edu (????
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