Hi, I tried to test ml using "-pc_type ml" on my problem. It was working ok using LU or hypre/boomeramg. However I got the warning:
Gen_Prolongator warning : max eigen <= 0.0 Gen_Prolongator warning : max eigen <= 0.0 Gen_Prolongator warning : max eigen <= 0.0 Gen_Prolongator warning : max eigen <= 0.0 Gen_Prolongator warning : max eigen <= 0.0 When I use hypre, I used "-pc_type hypre -pc_hypre_type boomeramg which gives good and fast result for solving my poisson eqn. Is there a recommendation for ml as well? Moreover, although I got answers from ml, my answer using ml differs from LU and hypre from the 3 sig. fig. When I run the example ex2f, I get different norms of error: LU: Norm of error 0.1192E-05 iterations 4 hypre: Norm of error < 1.e-12,iterations 1 ml: Norm of error 0.2098E-03 iterations 2 It seems that norm of error for ml is a bit too high. How can I make it lower? Thank you. Hong Zhang wrote: > On Thu, 16 Aug 2007, Ben Tay wrote: > > >> Btw, is the file to download >> ftp://ftp.mcs.anl.gov/pub/petsc/externalpackages/ml-5.0.tar.gz? >> > > Yes. You can simply use '--download-ml=1' during configuration. > > Run your program with '-help' to see all options for using ml. > See ~petsc/src/ksp/ksp/examples/tests/ex26.c on how to use ML. > > Hong > > >> Thanks >> >> Matthew Knepley wrote: >> >>> The multigrid PC needs information about the grid and discretization. If you >>> cannot provide this, use AMG through Hypre or ML. Or if you have a >>> structured grid, consider using DMMG. >>> >>> Thanks, >>> >>> Matt >>> >>> On 8/15/07, Ben Tay <zonexo at gmail.com> wrote: >>> >>> >>>> Hi, >>>> >>>> I found that there's a multigrid option in the manual which can be used >>>> by adding -pctype mg -pcmgtype PC_MG_MULTIPLICATIVE. >>>> >>>> However, it seems that I am actually just using LU since with or without >>>> this option, I got exactly the same answer. Am I using multigrid the >>>> wrong way? >>>> >>>> Thanks >>>> >>>> >>>> >>>> >>> >>> >> > > >
