On Fri, Jun 22, 2012 at 12:15 PM, Anton Popov <popov at uni-mainz.de> wrote:
> Hi petsc team, > I have a question about using nested matrices and vectors for coupled > solution of Stokes system with filedsplit preconditioner. > > Is there a simple example explaining how I can create nested matrix and > vector using > "MatCreateNest" and "VecCreateNest" functions, provided that I already > have all constituting blocks correctly assembled? > I could not find these example online, and if I do it straightforwardly > according to documentation, petsc complains that some vector blocks are not > setup. > You do not need MatNest to use FS. Some of us have a crazy MatNest attachment, so it seems like you do, but it will work with any matrix. > Do I need to define velocity and pressure splits using > "PCFieldSplitSetIS", because if I don't, petsc says "Unhandled case, must > have at least two fields, not 1!"? > If you really have Stokes (a 0 pressure block), use -pc_fieldsplit_detect_saddle_point. > Do I need to explicitly specify the blocksize, if I want to use the > filedsplit preconditioner for the velocity block? > No. > A small example would be extremely helpful > SNES ex62 runs it, but you need my FEM assembly configured to do that. I will post instructions soon. Matt > Thanks a lot, > > Anton > > -- 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/20120622/557c6386/attachment.html>
