[petsc-dev] PETSc MG Solvers vs agmg

[Dave Nystrom]

Barry Smith writes:
 > 
 > 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.

Thanks for the info.

 > > 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.

http://homepages.ulb.ac.be/~ynotay/AGMG

 > Barry
 > 
 > > 
 > > Thanks,
 > > 
 > > Dave