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 > ------------------------------------------------------------------------------ Time is money. Stop wasting it! Get your web API in 5 minutes. www.restlet.com/download http://p.sf.net/sfu/restlet _______________________________________________ Libmesh-users mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/libmesh-users
