Try the following solver options: -pc_type lu -pc_factor_mat_solver_package superlu
What was the output from the -ksp_monitor_singular_value ? Thanks. On Thu, May 29, 2014 at 6:52 PM, walter kou <[email protected]> wrote: > Hi Vikram, > > How to try using just lu or super lu? I am pretty ignorant in playing with > proper ksp options in the command line. > > Could you point out any introductory materials on this? > > Thanks so much. > > > > > On Wed, May 28, 2014 at 11:54 AM, Vikram Garg <[email protected]> > wrote: > >> 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. >>> > >>> >>> ------------------------------------------------------------------------------ >>> The best possible search technologies are now affordable for all >>> companies. >>> Download your FREE open source Enterprise Search Engine today! >>> Our experts will assist you in its installation for $59/mo, no >>> commitment. >>> Test it for FREE on our Cloud platform anytime! >>> >>> http://pubads.g.doubleclick.net/gampad/clk?id=145328191&iu=/4140/ostg.clktrk >>> _______________________________________________ >>> Libmesh-users mailing list >>> [email protected] >>> https://lists.sourceforge.net/lists/listinfo/libmesh-users >>> >> >> >> >> -- >> Vikram Garg >> Postdoctoral Associate >> Center for Computational Engineering >> Massachusetts Institute of Technology >> http://web.mit.edu/vikramvg/www/ >> >> http://www.runforindia.org/runners/vikramg >> > > -- Vikram Garg Postdoctoral Associate Center for Computational Engineering Massachusetts Institute of Technology http://web.mit.edu/vikramvg/www/ http://www.runforindia.org/runners/vikramg ------------------------------------------------------------------------------ Time is money. 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