optimize and simplify computing relevant_dofs

simplify logic in extract_locally_relevant_dofs and
extract_locally_relevant_mg_dofs. A benchmark shows that the new
approach is faster.

diff --git a/source/dofs/dof_tools.cc b/source/dofs/dof_tools.cc
index 55ea3f86642fe6ae59f6422a8cde600780a83053..7ae323db0de0ae848aab9085acae07c8e0d997d2 100644 (file)
--- a/source/dofs/dof_tools.cc
+++ b/source/dofs/dof_tools.cc
@@ -946,11 +946,14 @@ namespace DoFTools
     // collect all the locally owned dofs
     dof_set = dof_handler.locally_owned_dofs();
 
-    // add the DoF on the adjacent ghost cells to the IndexSet, cache them
-    // in a set. need to check each dof manually because we can't be sure
-    // that the dof range of locally_owned_dofs is really contiguous.
+    // now add the DoF on the adjacent ghost cells to the IndexSet
+
+    // Note: It is not worth it to cache intermediate data in a set because
+    // add_indices is more efficient. I also benchmarked skipping the
+    // locally_owned_dofs by doing locally_owned_dofs().is_element() but
+    // that is also slower unless 70%+ of the DoFs are locally owned and they
+    // are contiguous. - Timo Heister
     std::vector<types::global_dof_index> dof_indices;
-    std::set<types::global_dof_index> global_dof_indices;
 
     typename DH::active_cell_iterator cell = dof_handler.begin_active(),
                                       endc = dof_handler.end();
@@ -959,16 +962,9 @@ namespace DoFTools
         {
           dof_indices.resize(cell->get_fe().dofs_per_cell);
           cell->get_dof_indices(dof_indices);
-
-          for (std::vector<types::global_dof_index>::iterator it=dof_indices.begin();
-               it!=dof_indices.end();
-               ++it)
-            if (!dof_set.is_element(*it))
-              global_dof_indices.insert(*it);
+          dof_set.add_indices(dof_indices.begin(), dof_indices.end());
         }
 
-    dof_set.add_indices(global_dof_indices.begin(), global_dof_indices.end());
-
     dof_set.compress();
   }
 
@@ -982,11 +978,14 @@ namespace DoFTools
     // collect all the locally owned dofs
     dof_set = dof_handler.locally_owned_mg_dofs(level);
 
-    // add the DoF on the adjacent ghost cells to the IndexSet, cache them
-    // in a set. need to check each dof manually because we can't be sure
-    // that the dof range of locally_owned_dofs is really contiguous.
+    // add the DoF on the adjacent ghost cells to the IndexSet
+
+    // Note: It is not worth it to cache intermediate data in a set because
+    // add_indices is more efficient. I also benchmarked skipping the
+    // locally_owned_dofs by doing locally_owned_dofs().is_element() but
+    // that is also slower unless 70%+ of the DoFs are locally owned and they
+    // are contiguous. - Timo Heister
     std::vector<types::global_dof_index> dof_indices;
-    std::set<types::global_dof_index> global_dof_indices;
 
     typename DH::cell_iterator cell = dof_handler.begin(level),
                                endc = dof_handler.end(level);
@@ -1001,16 +1000,9 @@ namespace DoFTools
 
         dof_indices.resize(cell->get_fe().dofs_per_cell);
         cell->get_mg_dof_indices(dof_indices);
-
-        for (std::vector<types::global_dof_index>::iterator it=dof_indices.begin();
-             it!=dof_indices.end();
-             ++it)
-          if (!dof_set.is_element(*it))
-            global_dof_indices.insert(*it);
+        dof_set.add_indices(dof_indices.begin(), dof_indices.end());
       }
 
-    dof_set.add_indices(global_dof_indices.begin(), global_dof_indices.end());
-
     dof_set.compress();
   }