From e44161e8e65eb3c4666b82853c47b16c6aaeeaae Mon Sep 17 00:00:00 2001
From: bangerth <bangerth@0785d39b-7218-0410-832d-ea1e28bc413d>
Date: Thu, 26 Apr 2012 07:58:10 +0000
Subject: [PATCH] Add an assertion and document why the function can't work in
 this context.

git-svn-id: https://svn.dealii.org/trunk@25448 0785d39b-7218-0410-832d-ea1e28bc413d
---
 deal.II/include/deal.II/dofs/dof_tools.h | 16 ++++++++++++++++
 deal.II/source/dofs/dof_tools.cc         |  9 ++++++++-
 2 files changed, 24 insertions(+), 1 deletion(-)

diff --git a/deal.II/include/deal.II/dofs/dof_tools.h b/deal.II/include/deal.II/dofs/dof_tools.h
index fb15726895..633d040ec4 100644
--- a/deal.II/include/deal.II/dofs/dof_tools.h
+++ b/deal.II/include/deal.II/dofs/dof_tools.h
@@ -1114,6 +1114,22 @@ namespace DoFTools
                                     * non-zero components. Elements
                                     * in the mask corresponding to
                                     * later components are ignored.
+                                    *
+                                    * @note This function will not work
+                                    * for DoFHandler objects that are
+                                    * built on a
+                                    * parallel::distributed::Triangulation
+                                    * object. The reasons is that the
+                                    * output argument @p selected_dofs
+                                    * has to have a length equal to <i>all</i>
+                                    * global degrees of freedom.
+                                    * Consequently, this does not scale
+                                    * to very large problems. If you
+                                    * need the functionality of this
+                                    * function for parallel triangulations,
+                                    * then you need to use the other
+                                    * DoFTools::extract_boundary_dofs
+                                    * function.
                                     */
   template <class DH>
   void
diff --git a/deal.II/source/dofs/dof_tools.cc b/deal.II/source/dofs/dof_tools.cc
index d25e6df7cb..f865b18bf2 100644
--- a/deal.II/source/dofs/dof_tools.cc
+++ b/deal.II/source/dofs/dof_tools.cc
@@ -3752,9 +3752,16 @@ namespace DoFTools
                          std::vector<bool>             &selected_dofs,
                          const std::set<types::boundary_id_t> &boundary_indicators)
   {
-    AssertDimension (component_select.size(),n_components(dof_handler));
+    AssertDimension (component_select.size(), n_components(dof_handler));
     Assert (boundary_indicators.find (types::internal_face_boundary_id) == boundary_indicators.end(),
             ExcInvalidBoundaryIndicator());
+    Assert ((dynamic_cast<const parallel::distributed::Triangulation<DH::dimension,DH::space_dimension>*>
+             (&dof_handler.get_tria())
+             ==
+             0),
+            ExcMessage ("This function can not be used with distributed triangulations."
+                        "See the documentation for more information."));
+
     const unsigned int dim=DH::dimension;
 
                                      // let's see whether we have to
-- 
2.39.5