Hey Walter,
Have you tried using just lu or super lu ? You might
also want to check and see whats the output for -ksp_monitor_singular_value
and increase the gmres restart steps.
Thanks.
On Mon, May 26, 2014 at 1:57 PM, walter kou <[email protected]> wrote:
> Hi all,
> I ran a larger case: with elements = 200, and found for each calculation in
> the iteration, system.final_linear_residual() is about 0.5%.
>
> 1) Is the system.final_linear_residual() r = b -A X* (X* is the solution)
> ? right?
>
> 2) It seems final residual is too big, and the equation is not solved well
> (here |b| is about 1e-4). Does anyone have suggestion in playing with
> solvers of Ax=b?
> Here my case is on nonlinear elasticity, and A is almost symmetrical
> positive definite (only components influenced by boundary conditions will
> break the symmetry).
>
>
> Also, following the suggestion of Paul, I use -ksp_view and find my solver
> information is as below:
>
> KSP Object: 4 MPI processes
> type: gmres
> GMRES: restart=30, using Classical (unmodified) Gram-Schmidt
> Orthogonalization with no iterative refinement
> GMRES: happy breakdown tolerance 1e-30
> maximum iterations=250
> tolerances: relative=1e-08, absolute=1e-50, divergence=10000
> left preconditioning
> using nonzero initial guess
> using PRECONDITIONED norm type for convergence test
> PC Object: 4 MPI processes
> type: bjacobi
> block Jacobi: number of blocks = 4
> Local solve is same for all blocks, in the following KSP and PC
> objects:
> KSP Object: (sub_) 1 MPI processes
> type: preonly
> maximum iterations=10000, initial guess is zero
> tolerances: relative=1e-05, absolute=1e-50, divergence=10000
> left preconditioning
> using NONE norm type for convergence test
> PC Object: (sub_) 1 MPI processes
> type: ilu
> ILU: out-of-place factorization
> 0 levels of fill
> tolerance for zero pivot 2.22045e-14
> using diagonal shift to prevent zero pivot
> matrix ordering: natural
> factor fill ratio given 1, needed 1
> Factored matrix follows:
> Matrix Object: 1 MPI processes
> type: seqaij
> rows=324, cols=324
> package used to perform factorization: petsc
> total: nonzeros=16128, allocated nonzeros=16128
> total number of mallocs used during MatSetValues calls =0
> not using I-node routines
> linear system matrix = precond matrix:
> Matrix Object: () 1 MPI processes
> type: seqaij
> rows=324, cols=324
> total: nonzeros=16128, allocated nonzeros=19215
> total number of mallocs used during MatSetValues calls =0
> not using I-node routines
> linear system matrix = precond matrix:
> Matrix Object: () 4 MPI processes
> type: mpiaij
> rows=990, cols=990
> total: nonzeros=58590, allocated nonzeros=64512
> total number of mallocs used during MatSetValues calls =0
> not using I-node (on process 0) routines
>
>
>
> /*********************************************************
> Thanks,
>
> Walter
>
>
> On Thu, May 22, 2014 at 12:18 PM, Paul T. Bauman <[email protected]>
> wrote:
>
> >
> >
> >
> > On Thu, May 22, 2014 at 12:11 PM, walter kou <[email protected]
> >wrote:
> >
> >> OK, but libMesh calls a library, defaulting to PETSc if it's installed.
> >> Which library are you using?
> >>
> >> PETSc-3.3
> >>
> >
> > I recommend checking out the PETSc documentation (
> > http://www.mcs.anl.gov/petsc/petsc-as/documentation/) and tutorials. But
> > you'll want to start with -ksp_view to get the parameters PETSc is using.
> >
>
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--
Vikram Garg
Postdoctoral Associate
Center for Computational Engineering
Massachusetts Institute of Technology
http://web.mit.edu/vikramvg/www/
http://www.runforindia.org/runners/vikramg
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