On Mon, May 4, 2009 at 2:56 PM, Randall Mackie <rlmackie862 at gmail.com>wrote:
> Jed, > > Can you explain how to tell if the matrix is truly blocked? What's the > difference between a blocked matrix and one with several degrees of freedom > at each node, or are they the same thing? I'm solving Maxwell's equations > in 3D, so I have three vector field components at each node, is that what > you mean by blocked? Yes, that is blocked. Matt > > Thanks, Randy > > > Jed Brown wrote: > >> Ryan Yan wrote: >> >>> Could you make a little bit more clarification >>> on why the MatSetValuesBlocked() have some advantage on blocked >>> structure? >>> >> >> In addition to the assembly advantages that Satish pointed out, BAIJ >> requires less storage for the column indices, effectively improving the >> arithmetic intensity of many kernels, and speeding up matrix >> factorization (e.g. symbolic factorization only needs to compute fill in >> terms of blocks instead of individual elements). The use of inodes with >> AIJ (default when applicable) reduces the memory bandwidth requirements >> of the column indices, turns point relaxation smoothers (SOR) into >> stronger block relaxation, and allows a certain amount of unrolling. >> BAIJ requires even less metadata, provides more regular memory access, >> and does more unrolling. >> >> If your matrix is truly blocked, BAIJ should provide better performance >> with all preconditioners that support it. Many third-party >> preconditioners will not work with BAIJ, so it is useful to give your >> matrix a prefix (or check the options database if you are getting your >> matrix from a DA or similar) so that you can set it's type with >> -foo_mat_type when using a preconditioner that requires it. >> >> Jed >> >> -- 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 -------------- next part -------------- An HTML attachment was scrubbed... URL: <http://lists.mcs.anl.gov/pipermail/petsc-users/attachments/20090504/01c23a6b/attachment-0001.htm>
