On Tue, May 1, 2012 at 6:18 PM, Karthik Duraisamy <dkarthik at stanford.edu>wrote:
> Hello, > > Sorry (and thanks for the reply). I've attached the no multigrid case. I > didn't include it because (at least to the untrained eye, everything looks > the same). > Did you send all the output from the MG case? There must be a PC around it. By default its GMRES, so there would be an extra GMRES loop compared to the case without MG. Matt > Regards, > Karthik > > KSP Object: 8 MPI processes > type: gmres > GMRES: restart=100, using Classical (unmodified) Gram-Schmidt > Orthogonalization with no iterative refinement > GMRES: happy breakdown tolerance 1e-30 > maximum iterations=1 > using preconditioner applied to right hand side for initial guess > tolerances: relative=1e-05, absolute=1e-50, divergence=1e+10 > left preconditioning > using nonzero initial guess > using PRECONDITIONED norm type for convergence test > PC Object: 8 MPI processes > type: bjacobi > block Jacobi: number of blocks = 8 > 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 1e-12 > 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=9015, cols=9015 > package used to perform factorization: petsc > total: nonzeros=517777, allocated nonzeros=517777 > total number of mallocs used during MatSetValues calls =0 > using I-node routines: found 3476 nodes, limit used is 5 > linear system matrix = precond matrix: > Matrix Object: 1 MPI processes > type: seqaij > rows=9015, cols=9015 > total: nonzeros=517777, allocated nonzeros=517777 > total number of mallocs used during MatSetValues calls =0 > using I-node routines: found 3476 nodes, limit used is 5 > linear system matrix = precond matrix: > Matrix Object: 8 MPI processes > type: mpiaij > rows=75000, cols=75000 > total: nonzeros=4427800, allocated nonzeros=4427800 > total number of mallocs used during MatSetValues calls =0 > using I-node (on process 0) routines: found 3476 nodes, limit used is > 5 > > > ----- Original Message ----- > From: "Matthew Knepley" <knepley at gmail.com> > To: "PETSc users list" <petsc-users at mcs.anl.gov> > Sent: Tuesday, May 1, 2012 3:15:14 PM > Subject: Re: [petsc-users] Multigrid > > > On Tue, May 1, 2012 at 6:12 PM, Karthik Duraisamy < dkarthik at stanford.edu> > wrote: > > > > Hello Barry, > > Thank you for your super quick response. I have attached the output of > ksp_view and it is practically the same as that when I don't use PCMG. The > part I don't understand is how PCMG able to function at the zero grid level > and still produce a much better convergence than when using the default PC. > Is there any additional smoothing or interpolation going on? > > > > You only included one output, so I have no way of knowing what you used > before. However, this is running GMRES/ILU. > > > Also, for Algebraic Multigrid, would you recommend BoomerAMG or ML ? > > > > They are different algorithms. Its not possible to say generally that one > is better. Try them both. > > > Matt > > > Best regards, > Karthik. > > type: mg > MG: type is MULTIPLICATIVE, levels=1 cycles=v > Cycles per PCApply=1 > Not using Galerkin computed coarse grid matrices > Coarse grid solver -- level ------------------------------- > KSP Object: (mg_levels_0_) 8 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=1, initial guess is zero > tolerances: relative=1e-05, absolute=1e-50, divergence=10000 > left preconditioning > using PRECONDITIONED norm type for convergence test > PC Object: (mg_levels_0_) 8 MPI processes > type: bjacobi > block Jacobi: number of blocks = 8 > Local solve is same for all blocks, in the following KSP and PC objects: > KSP Object: (mg_levels_0_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: (mg_levels_0_sub_) 1 MPI processes > type: ilu > ILU: out-of-place factorization > 0 levels of fill > tolerance for zero pivot 1e-12 > 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=9015, cols=9015 > package used to perform factorization: petsc > total: nonzeros=517777, allocated nonzeros=517777 > total number of mallocs used during MatSetValues calls =0 > using I-node routines: found 3476 nodes, limit used is 5 > linear system matrix = precond matrix: > Matrix Object: 1 MPI processes > type: seqaij > rows=9015, cols=9015 > total: nonzeros=517777, allocated nonzeros=517777 > total number of mallocs used during MatSetValues calls =0 > using I-node routines: found 3476 nodes, limit used is 5 > linear system matrix = precond matrix: > Matrix Object: 8 MPI processes > type: mpiaij > rows=75000, cols=75000 > total: nonzeros=4427800, allocated nonzeros=4427800 > total number of mallocs used during MatSetValues calls =0 > using I-node (on process 0) routines: found 3476 nodes, limit used is 5 > linear system matrix = precond matrix: > Matrix Object: 8 MPI processes > type: mpiaij > rows=75000, cols=75000 > total: nonzeros=4427800, allocated nonzeros=4427800 > total number of mallocs used during MatSetValues calls =0 > using I-node (on process 0) routines: found 3476 nodes, limit used is 5 > > > > ----- Original Message ----- > From: "Barry Smith" < bsmith at mcs.anl.gov > > To: "PETSc users list" < petsc-users at mcs.anl.gov > > Sent: Tuesday, May 1, 2012 1:39:26 PM > Subject: Re: [petsc-users] Multigrid > > > On May 1, 2012, at 3:37 PM, Karthik Duraisamy wrote: > > > Hello, > > > > I have been using PETSc for a couple of years with good success, but > lately as my linear problems have become stiffer (condition numbers of the > order of 1.e20), I am looking to use better preconditioners. I tried using > PCMG with all the default options (i.e., I just specified my preconditioner > as PCMG and did not add any options to it) and I am immediately seeing > better convergence. > > > > What I am not sure of is why? I would like to know more about the > default parameters (the manual is not very explicit) and more importantly, > want to know why it is working even when I haven't specified any grid > levels and coarse grid operators. Any > > help in this regard will be appreciated. > > First run with -ksp_view to see what solver it is actually using. > > Barry > > > > > Also, ultimately I want to use algebraic multigrid so is PCML a better > option than BoomerAMG? I tried BoomerAMG with mixed results. > > > > Thanks, > > Karthik > > > > > > > > -- > > > > ======================================= > > Karthik Duraisamy > > Assistant Professor (Consulting) > > Durand Building Rm 357 > > Dept of Aeronautics and Astronautics > > Stanford University > > Stanford CA 94305 > > > > Phone: 650-721-2835 > > Web: www.stanford.edu/~dkarthik > > ======================================= > > > > > > -- > What most experimenters take for granted before they begin their > experiments is infinitely more interesting than any results to which their > experiments lead. > -- Norbert Wiener > -- What most experimenters take for granted before they begin their experiments is infinitely more interesting than any results to which their experiments lead. -- Norbert Wiener -------------- next part -------------- An HTML attachment was scrubbed... URL: <http://lists.mcs.anl.gov/pipermail/petsc-users/attachments/20120501/7fa99aba/attachment.htm>
