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