[petsc-dev] PETSc MG Solvers vs agmg
Barry Smith
bsmith at mcs.anl.gov
Tue May 1 08:40:11 CDT 2012
On May 1, 2012, at 8:34 AM, Dave Nystrom wrote:
> I have a 2d resistive mhd code that has an interface to both agmg and various
> multigrid solvers available from PETSc including gamg, hypre and ml. I'm not
> that familiar with multigrid and so it is difficult for me to know how to
> experiment with the various mg packages and tune them to my particular
> problems. In my code, agmg is a stand alone solver. I have a couple of
> questions.
>
> 1. Is it possible to use the PETSc mg solvers effectively without an
> iterative method by choosing preonly as the iterative method - like I do for
> the PETSc direct solves?
Use -ksp_type richardson Note that using -ksp_type preonly would result in only 1 iteration of the multigrid method and hence not what you want.
Note that algebraic multigrid methods are generally designed to be used with a Krylov accelerator and convergence may suffer (i.e. it will take longer or not even converge) without a Krylov accelerator. Though, of course, experimenting to find the fastest is a good idea.
>
> 2. Is anyone on this list sufficiently familiar with agmg and the other
> PETSc mg solvers to know how to configure the PETSc mg solvers to work more
> like agmg? It seems that agmg gives better performance than the PETSc mg
> solvers but I also have issues with agmg including fragility.
Please send a link for information on agmg; I've never heard of that.
Barry
>
> Thanks,
>
> Dave
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