If what you want to do is apply a block preconditioner to a matrix arising from a regular grid, DA can already do this automatically. This uses the PCFieldSplit, and can be completely controlled from the command line. It is designed to do these sorts of things.
I do not understand your last question. Matt On Fri, Jan 29, 2010 at 11:29 AM, Michel Cancelliere <fernandez858 at gmail.com > wrote: > Thank you for your promptly response, i will use unsorted inex set as > you suggest (because my submatrices are very large (4 submatrices N/2 > x N/2 from the original one Nx N), > I realize that i cannot use block matrices because the reordering > split within the blocks and the resulting matrices are not block > matrices anymore. In terms of performance how much can affect this to > the code, in the sense if i apply for example an ILU preconditioner to > a block matrix (baij) and solve the same system but this time using an > aij matrix ? not sure if it is clear > > Thanks > Michel > > > > > On 1/29/10, Jed Brown <jed at 59a2.org> wrote: > > On Fri, 29 Jan 2010 09:43:05 -0600 (CST), abhyshr at mcs.anl.gov wrote: > >> Instead of calling MatGetSubMatrix to get each submatrix you can use > >> MatGetSubMatrices to extract several submatrices at once. See > >> > http://www.mcs.anl.gov/petsc/petsc-as/snapshots/petsc-current/docs/manualpages/Mat/MatGetSubMatrices.html#MatGetSubMatrices > . > > > > I don't think Michel was asking to extract multiple matrices. In > > serial, MatGetSubMatrices is implemented by calling MatGetSubMatrix so > > there is no weaker assumption on index set sortedness. > > > > 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/20100129/6156b1b1/attachment.htm>
