Add comment about a case where we had a TODO previously.

git-svn-id: https://svn.dealii.org/trunk@4891 0785d39b-7218-0410-832d-ea1e28bc413d

diff --git a/deal.II/deal.II/source/numerics/matrices.cc b/deal.II/deal.II/source/numerics/matrices.cc
index 8d59abe53d3f7446fad785a3f26b4658254401b7..f8a70f1f27641854f8b7c6090ccf71d14e26154c 100644 (file)
--- a/deal.II/deal.II/source/numerics/matrices.cc
+++ b/deal.II/deal.II/source/numerics/matrices.cc
@@ -671,9 +671,35 @@ create_boundary_mass_matrix_1 (const Mapping<dim>        &mapping,
                           cell_matrix(i,j));
              else
                {
-//TODO:[?] We assume here that shape functions that have support also on the boundary also have their support point on the boundary (by having their indices in dof_is_on_face set true). This is not true, however, e.g. for discontinuous elements.
-                                                  // compare here for relative
-                                                  // smallness
+                                                  // assume that all
+                                                  // shape functions
+                                                  // that are nonzero
+                                                  // on the boundary
+                                                  // are also listed
+                                                  // in the
+                                                  // @p{dof_to_boundary}
+                                                  // mapping. if that
+                                                  // is not the case,
+                                                  // then the
+                                                  // boundary mass
+                                                  // matrix does not
+                                                  // make that much
+                                                  // sense anyway, as
+                                                  // it only contains
+                                                  // entries for
+                                                  // parts of the
+                                                  // functions living
+                                                  // on the boundary
+                                                  //
+                                                  // these, we may
+                                                  // compare here for
+                                                  // relative
+                                                  // smallness of all
+                                                  // entries in the
+                                                  // local matrix
+                                                  // which are not
+                                                  // taken over to
+                                                  // the global one
                  Assert (std::fabs(cell_matrix(i,j)) <= 1e-10 * max_diag_entry,
                          ExcInternalError ());
                };