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
