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
