Hi Jed, Thanks for your reply. The assembled matrix I have corresponds to the full problem on the full mesh. There are no "Neumann" problems (or any sort of domain decomposition) defined in the code generates the matrix. However, I think assembling the full problem is equivalent to implicitly assembling the "Neumann" problems, since the system can be partitioned as;
[A_{LL} | A_{LI}] [u_L] [F] -----------|------------ -------- = ----- [A_{IL} |A_{II} ] [u_I] [G] and G should correspond to the Neumann problem. I might be thinking wrong (or maybe I completely misunderstood the idea), if so please correct me. But I think that the problem is that I am not explicitly telling PCBDDC which dofs are interface dofs. Regards, Abdullah Ali Sivas On Tue, 23 Oct 2018 at 23:16, Jed Brown <j...@jedbrown.org> wrote: > Did you assemble "Neumann" problems that are compatible with your > definition of interior/interface degrees of freedom? > > Abdullah Ali Sivas <abdullahasi...@gmail.com> writes: > > > Dear all, > > > > I have a series of linear systems coming from a PDE for which BDDC is an > > optimal preconditioner. These linear systems are assembled and I read > them > > from a file, then convert into MATIS as required (as in > > > https://www.mcs.anl.gov/petsc/petsc-current/src/ksp/ksp/examples/tutorials/ex72.c.html > > ). I expect each of the systems converge to the solution in almost same > > number of iterations but I don't observe it. I think it is because I do > not > > provide enough information to the preconditioner. I can get a list of > inner > > dofs and interface dofs. However, I do not know how to use them. Has > anyone > > have any insights about it or done something similar? > > > > Best wishes, > > Abdullah Ali Sivas >