I don't think bjacobi is working on GPUs. I know Dominic made a pull request a few months ago, but I don't know if its been integrated into next. -Paul
On Mon, May 19, 2014 at 12:45 PM, Matthew Knepley <[email protected]> wrote: > On Mon, May 19, 2014 at 1:42 PM, Jonathan Wong <[email protected]>wrote: > >> Thanks for the input. To clarify, I'm trying to compare GPU algorithms to >> Petsc, and they only have cg/jacobi for what I'm comparing at the moment. >> This is why I'm not using gmres (which also works well). >> >> I can solve the problem with the GPU (custom code) using CG + jacobi for >> all the meshes. On the CPU side, I can solve everything with cg/bjacobi and >> almost all of my meshes with cg/jacobi except for my 50k node mesh. I can >> solve the problem with my finite element built-in direct solver (just takes >> awhile) on one processor. I've been reading that by default the bjacobi pc >> uses one block per processor. So I had assumed that for one processor >> block-jacobi and jacobi would give similar results. cg+bjacobi works fine. >> cg+jacobi does not. >> > > "Jacobi" means preconditioning by the inverse of the diagonal of the > matrix. Block-Jacobi means using a preconditioner > formed from each of the blocks, in this case 1 block. By default the inner > preconditioner is ILU(0), not jacobi. You can > make them equivalent using -sub_pc_type jacobi. > > Matt > > >> I'll just look into the preconditioner code and use KSPview to try to >> figure out what the differences are for one processor. I'm not sure why the >> GPU can consistently solve the problem with cg/jacobi. I'm assuming this is >> due to the way round-off or the order of operations differences between the >> two. >> >> >> On Mon, May 19, 2014 at 6:35 AM, Jed Brown <[email protected]> wrote: >> >>> Matthew Knepley <[email protected]> writes: >>> > No, Block-Jacobi and Jacobi are completely different. If you are not >>> > positive definite, you should be using MINRES. >>> >>> MINRES requires an SPD preconditioner. >>> >> >> > > > -- > 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 >
