[CIG-SHORT] PyLith problems

[Brad Aagaard]

Jiangning-

I don't follow what you are trying to do. I can run the examples/3d/tet4 with 
the asm precondition without any problems. As I mentioned previously, there 
is no magic preconditioner for all problems. Finding the best one for the 
problem you are solving will require some intuition, experience, and a little 
experimentation.

If the problem runs but you get unexpected results for a given preconditioner, 
it may be suggesting that something is wrong with the mesh or the problem 
setup. I recommend starting with mesh/parameters that seem to work and 
incrementally work towards the problem you want to solve to isolate where the 
problem may be originating.

Brad

On Thursday 06 December 2007, Jiangning Lu wrote:
> Hi Brad,
>
> I'm using the same boundary conditions in this model with the
> example/3d/tet4/dislocation case.
>
> Using the same mesh,I also run another problem successfully without a fault
> specified. From this can I say that the material ids are correct? In other
> words, specifying a fault will not change the material id settings?
>
> Thanks,
>
> Jiangning
>
> Quoting Brad Aagaard <baagaard at usgs.gov>:
> > 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 (????
> >> _______________________________________________
> >> CIG-SHORT mailing list
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> >
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>
> ---
> Jiangning Lü
> 54-521     x3-6389
> Geophysics
> EAPS, MIT
> johnnylu at mit.edu (????