Ben, > > 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
I got the same warning on using ML for my application, which results in unacceptable computational result in my case. I've sent a request to ML developer for its interpretation yesterday. > 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 You may test other available options (see -help), in particular, find out the smoother and MG cycle used by hypre and apply the same to ML. Good luck, Hong > > 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 > >>>> > >>>> > >>>> > >>>> > >>> > >>> > >> > > > > > > > >
