]> https://gitweb.dealii.org/ - dealii-svn.git/commitdiff
Add a comment to the place where we skip copying elements into Trilinos.
authorbangerth <bangerth@0785d39b-7218-0410-832d-ea1e28bc413d>
Wed, 13 Aug 2008 03:08:02 +0000 (03:08 +0000)
committerbangerth <bangerth@0785d39b-7218-0410-832d-ea1e28bc413d>
Wed, 13 Aug 2008 03:08:02 +0000 (03:08 +0000)
git-svn-id: https://svn.dealii.org/trunk@16532 0785d39b-7218-0410-832d-ea1e28bc413d

deal.II/examples/step-31/step-31.cc

index df879ac0a416193986c642fbadab3110d9b62443..7e17aa1e92b28260acd9999704cd8331c8cd07bf 100644 (file)
@@ -177,8 +177,20 @@ TrilinosAmgPreconditioner<dim>::TrilinosAmgPreconditioner(
                vector_valued_problem (VectorValuedProblem)
 {
   
-                                // Init Epetra Matrix, avoid 
-                                // storing the nonzero elements.
+                                // Init Epetra Matrix. Even though we build
+                                // up the sparsity pattern to only include
+                                // those entries that actually couple, there
+                                // are quite a number of entries in the
+                                // sparse matrix that are actually zero
+                                // (these are at rows or columns that
+                                // correspond to degrees of freedom that are
+                                // either constrained by hanging nodes or by
+                                // boundary values). We avoid copying these
+                                // nonzero elements to the Trilinos matrix to
+                                // keep the preconditioner as compact as
+                                // possible. While this increases the number
+                                // of outer iterations by a tiny bit but
+                                // makes the overall scheme faster.
   {
     Map.reset (new Epetra_Map(n_u, 0, communicator));
     

In the beginning the Universe was created. This has made a lot of people very angry and has been widely regarded as a bad move.

Douglas Adams


Typeset in Trocchi and Trocchi Bold Sans Serif.