On Mon, Jul 25, 2016 at 3:17 PM, Ari Rappaport <[email protected]> wrote:
> Hi there! > I am a student intern at Voss Scientific, a contractor for national labs. > I have been researching multigrid methods this summer. My office has an > established particle code which uses petsc libraries for matrix solutions. > There is an interest in using multigrid methods to precondition our > matrices. We have attempted to use the Algebraic Multigrid Preconditioner > on our field solver and it was quite effective with one processor. However, > when we moved to four processors the PCAMG took about 1000 times as many > iterations. I am wondering if there are any special considerations that > need to be made for using AMG on multiple domains which in turn means > multiple processors? Also, I understand there is also a PCMG option that > takes advantage of the actual grid structure of the problem. I am also > wondering if this could improve preconditioning. > 1) For all convergence questions, we need to see the output of -ksp_monitor_true_residual -ksp_view -ksp_converged_reason 2) Are you solving an elliptic equation? 3) GAMG should give about the same convergence in parallel, but I do not know what you used until I see -ksp_view output Matt > Thanks, > Ari > -- What most experimenters take for granted before they begin their experiments is infinitely more interesting than any results to which their experiments lead. -- Norbert Wiener
