From a7f5e639a541b1567cbfd0616516cb54e9c38978 Mon Sep 17 00:00:00 2001 From: Wolfgang Bangerth Date: Fri, 2 Sep 2005 15:14:28 +0000 Subject: [PATCH] Add another comment. git-svn-id: https://svn.dealii.org/trunk@11358 0785d39b-7218-0410-832d-ea1e28bc413d --- deal.II/examples/step-18/step-18.cc | 26 ++++++++++++++++++++++++++ 1 file changed, 26 insertions(+) diff --git a/deal.II/examples/step-18/step-18.cc b/deal.II/examples/step-18/step-18.cc index fdab1b19de..8c368015eb 100644 --- a/deal.II/examples/step-18/step-18.cc +++ b/deal.II/examples/step-18/step-18.cc @@ -1423,6 +1423,32 @@ namespace QuasiStaticElasticity // and we can build it even for large 3d // problems. // + // It is also worth noting that the + // sparsity pattern we construct is + // global, i.e. comprises all degrees of + // freedom whether they will be owned by + // the processor we are on or another one + // (in case this program is run in + // parallel via MPI). This of course is + // not optimal -- it limits the size of + // the problems we can solve, since + // storing the entire sparsity pattern + // (even if only for a short time) on + // each processor does not scale + // well. However, there are several more + // places in the program in which we do + // this, for example we always keep the + // global triangulation and DoF handler + // objects around, even if we only work + // on part of them. At present, deal.II + // does not have the necessary facilities + // to completely distribute these objects + // (a task that, indeed, is very hard to + // achieve with adaptive meshes, since + // well-balanced subdivisions of a domain + // tend to become unbalanced as the mesh + // is adaptively refined). + // // With this data structure, we can then // go to the PETSc sparse matrix and tell // it to pre-allocate all the entries we -- 2.39.5