Hi Dmitry, Thanks very much. I will try if that works. Subramanya On Nov 26, 2013, at 4:03 PM, Dmitry Karpeyev <[email protected]> wrote:
> Ah, that might still be true, although that ought to be changed. > In any event, you can use the DM to set the bounds for the VI, > and set up PCFieldSplit as I explained in the previous email. > > Let me know if this works for you. > Cheers, > Dmitry. > > > On Tue, Nov 26, 2013 at 3:01 PM, Subramanya Sadasiva <[email protected]> > wrote: > Hi Dmitry, > I was under the impression that I needed to use the DM to use the VI solver. > Is that not the case? > Thanks, > Subramanya. > > On Nov 26, 2013, at 3:17 PM, Dmitry Karpeyev <[email protected]> wrote: > >> I assume you are referring to using the Schur-complement flavor of >> PCFieldSplit? >> How many variables do you have? Are they all C0? Is the basis nodal? If >> so, >> you don't necessarily need DMlibMesh: >> >> Assume you have m P1 variables (maybe m==2?). You can lay your degrees of >> freedom >> in the variable-major order (by this I mean having contiguous nodal >> coefficients corresponding >> to a given node -- maybe that's called 'node-major':-). >> Then use these options: >> -pc_type fieldsplit -pc_fieldsplit_block_size m -pc_fieldsplit_0_fields 0 >> -pc_fieldsplit_1_fields 1\ >> -pc_fieldsplit_type schur -pc_fieldsplit_schur_factorization_type full >> >> This will put the 0-th (in the zero-base C-speak) variable into the 0-th >> split, and the first variable >> in the first split. You can also permute the column blocks, if necessary, >> or put more variables >> into each split. You might try -pc_fieldsplit_schur_factorization_type >> upper or lower. >> >> The crucial part, however, is to have a good preconditioner for S, which in >> the terminology of the notes >> you sent is S = D - C inv(A) B. By default PETSc will use D as the >> preconditioner for S. That may >> or may not be good enough. Otherwise you will need to assemble a >> preconditioner for S, things >> will get more hairy, and we might need to put more support for that into >> libMesh. >> >> Hope this helps. >> Dmitry. >> >> >> On Tue, Nov 26, 2013 at 1:56 PM, Subramanya Sadasiva <[email protected]> >> wrote: >> >> Hi Dmitry, >> I am using the DM solver to solve a Cahn Hilliard equation using a C0 >> discretization. I would like to use the preconditioner used in >> >> http://www.mcs.anl.gov/~anitescu/Presentations/2011/anitescu-2011-SIAM-CSE-DVI.pdf >> >> >> I have been able to use the PETSC-DM solver with the VI solver to solve the >> Cahn Hilliard equation, but I haven’t been able to get a field-split >> preconditioner to work. >> >> Thanks, >> Subramanya >> >> >> On Nov 26, 2013, at 2:07 PM, Dmitry Karpeyev <[email protected]> wrote: >> >>> DMlibMesh should work, but it's in need of an overhaul and simplification. >>> Could you tell me how you intend to use it? That way we can figure out >>> what needs to be done to make it usable. >>> Thanks. >>> Dmitry. >>> >>> >>> On Thu, Nov 21, 2013 at 1:32 PM, subramanya sadasiva <[email protected]> >>> wrote: >>> Hi , I want to use petsc fieldsplit preconditioners with the petsc-dm >>> solver that has been implemented as part of libmesh. The last time I tried >>> it, I had trouble because dmcreatefielddecomposition was not being called. >>> Is there someone that could guide me with trying to correct this in >>> libmesh? Thanks, Subramanya >>> ------------------------------------------------------------------------------ >>> Shape the Mobile Experience: Free Subscription >>> Software experts and developers: Be at the forefront of tech innovation. >>> Intel(R) Software Adrenaline delivers strategic insight and game-changing >>> conversations that shape the rapidly evolving mobile landscape. Sign up now. >>> http://pubads.g.doubleclick.net/gampad/clk?id=63431311&iu=/4140/ostg.clktrk >>> _______________________________________________ >>> Libmesh-users mailing list >>> [email protected] >>> https://lists.sourceforge.net/lists/listinfo/libmesh-users >>> >>> >>> >>> -- >>> Dmitry Karpeev >>> Mathematics and Computer Science >>> Argonne National Laboratory >>> Argonne, Illinois, USA >>> and >>> Computation Institute >>> University of Chicago >>> 5735 S. Ellis Avenue >>> Chicago, IL 60637 >>> ----------------------- >>> Phone: 630-252-1229 >>> Fax: 630-252-5986 >> >> >> >> > > > > ------------------------------------------------------------------------------ Rapidly troubleshoot problems before they affect your business. Most IT organizations don't have a clear picture of how application performance affects their revenue. With AppDynamics, you get 100% visibility into your Java,.NET, & PHP application. Start your 15-day FREE TRIAL of AppDynamics Pro! http://pubads.g.doubleclick.net/gampad/clk?id=84349351&iu=/4140/ostg.clktrk _______________________________________________ Libmesh-users mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/libmesh-users
