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 Subject: Re: [OMPI users] 3D domain decomposition with MPI From: Eugene Loh (eugene.loh_at_[hidden]) Date: 2010-03-10 20:07:57 Next message: Eugene Loh: "Re: [OMPI users] 3D domain decomposition with MPI" Previous message: Gus Correa: "Re: [OMPI users] 3D domain decomposition with MPI" In reply to: Gus Correa: "Re: [OMPI users] 3D domain decomposition with MPI" Next in thread: Gus Correa: "Re: [OMPI users] 3D domain decomposition with MPI" Reply: Gus Correa: "Re: [OMPI users] 3D domain decomposition with MPI" Gus Correa wrote: > Also, I wonder why you want to decompose on both X and Y ("pencils"), > and not only X ("books"), > which may give you a smaller/simpler domain decomposition > and communication footprint. > Whether you can or cannot do this way depends on your > computation, which I don't know about. I'm not sure I'm following the entire thread, but higher-dimensional decompositions, though more complicated, can improve the communciation:computation ratio. For example, say you have a 100x100x100 grid to distribute over 100 processes. Even if you have only one ghost cell at each surface, a 1d decomposition would place a 1x100x100 "book" on each process with 2x100x100 ghost cells: a 2:1 ratio of ghost:real cells! That's a lot. In contrast, if you had 10x10x100 pencils, there would be (4*10+4)x100 ghosts. The ratio drops to 0.44. This is an extreme case, but it illustrates the point. Indeed, maybe you could even drop to a 25x20x20 "box". Then the ghost:real ratio might be around 0.29 or so. Next message: Eugene Loh: "Re: [OMPI users] 3D domain decomposition with MPI" Previous message: Gus Correa: "Re: [OMPI users] 3D domain decomposition with MPI" In reply to: Gus Correa: "Re: [OMPI users] 3D domain decomposition with MPI" Next in thread: Gus Correa: "Re: [OMPI users] 3D domain decomposition with MPI" Reply: Gus Correa: "Re: [OMPI users] 3D domain decomposition with MPI"