On Sat, May 16, 2020 at 5:12 PM Gary Hu <hugary1...@gmail.com> wrote:
> Hello all, > > I am new to libMesh. I am trying to solve a generalized eigen-value problem > for an integral equation. I tried example "Solving a generalized Eigen > Problem" and it works fine. > > Next, I modified the assembly routine to have a skeleton like this: > > for (const auto & elem : mesh.active_local_element_ptr_range()) > for (const auto & elem_remote : mesh.active_element_ptr_range()) > > So basically for each local element, I am looping over all the active > elements (local and nonlocal) to assemble the integral equation. I am > pretty confident that I used fe->reinit and other housekeeping stuff > properly. > It sounds like you are trying to build a dense matrix... in such a case all the extra "bookkeeping" indices etc. that are required for sparse matrices is not required, so this approach won't scale well. I think you may want to look into building a dense matrix for your method, e.g. MatCreateDense in PETSc [0]. We don't have C++ interfaces for MatDense in libMesh yet since our main focus is FEA but it's something I think we'd definitely like to have a PR adding. Regarding your original question, I don't see anything obviously wrong with the GhostingFunctor approach you are taking, so it may just be a coding bug that's causing it to not work. I'd start by adding print statements to check whether it's actually being called and what elements are being added to coupled_elements. I don't know how much time you want to spend debugging this approach though, because even if it works I fear it is going to be incredibly slow, not only due to the storing-dense-matrix-in-sparse-format issue, but also because of the N^2 assembly loop you've proposed above... perhaps there is an existing way to speed up whatever you are doing (fast multipole method?) which you should look into first. [0]: https://www.mcs.anl.gov/petsc/petsc-current/docs/manualpages/Mat/MatCreateDense.html -- John _______________________________________________ Libmesh-users mailing list Libmesh-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/libmesh-users
