From d60d1def46479a06826de1b496e96cdb203f1d9f Mon Sep 17 00:00:00 2001
From: Wolfgang Bangerth <bangerth@math.tamu.edu>
Date: Mon, 17 Apr 2000 14:33:12 +0000
Subject: [PATCH] Add extract_boundary_dofs.

git-svn-id: https://svn.dealii.org/trunk@2734 0785d39b-7218-0410-832d-ea1e28bc413d
---
 deal.II/deal.II/include/dofs/dof_tools.h | 51 ++++++++++++----
 deal.II/deal.II/source/dofs/dof_tools.cc | 75 ++++++++++++++++++++++++
 deal.II/doc/news/2000/c-3-0.html         |  4 ++
 3 files changed, 117 insertions(+), 13 deletions(-)

diff --git a/deal.II/deal.II/include/dofs/dof_tools.h b/deal.II/deal.II/include/dofs/dof_tools.h
index d571b1114d..657f849d6a 100644
--- a/deal.II/deal.II/include/dofs/dof_tools.h
+++ b/deal.II/deal.II/include/dofs/dof_tools.h
@@ -350,28 +350,53 @@ class DoFTools
 				      * are then flagged #true#, while all
 				      * others are set to #false#.
 				      *
-				      * The size of #select# shall equal
-				      * the number of components in the
-				      * finite element used by #dof#.
+				      * The size of #component_select#
+				      * shall equal the number of
+				      * components in the finite
+				      * element used by #dof#.
 				      */
     template <int dim>
     static void
-    extract_dofs(const DoFHandler<dim> &dof_handler,
-		 const vector<bool>    &select,
-		 vector<bool>          &selected_dofs);
+    extract_dofs (const DoFHandler<dim> &dof_handler,
+		  const vector<bool>    &component_select,
+		  vector<bool>          &selected_dofs);
 
 				     /**
-				      * Do the same thing as #extract_dofs#
-				      * for one level of a multi-grid DoF
-				      * numbering.
+				      * Do the same thing as
+				      * #extract_dofs# for one level
+				      * of a multi-grid DoF numbering.
 				      */
     template <int dim>
     static void
-    extract_level_dofs(const unsigned int       level,
-		       const MGDoFHandler<dim> &dof,
-		       const vector<bool>      &select,
-		       vector<bool>            &selected_dofs);
+    extract_level_dofs (const unsigned int       level,
+			const MGDoFHandler<dim> &dof,
+			const vector<bool>      &select,
+			vector<bool>            &selected_dofs);
 
+				     /**
+				      * Extract all degrees of freedom
+				      * which are at the boundary and
+				      * belong to specified components
+				      * of the solution. The function
+				      * returns its results in the
+				      * last parameter which contains
+				      * #true# is a degree of freedom
+				      * is at the boundary and belongs
+				      * to one of the selected
+				      * components, and #false#
+				      * otherwise.
+				      *
+				      * The size of #component_select#
+				      * shall equal the number of
+				      * components in the finite
+				      * element used by #dof#.
+				      */
+    template <int dim>
+    static void
+    extract_boundary_dofs (const DoFHandler<dim> &dof_handler,
+			   const vector<bool>    &component_select,
+			   vector<bool>          &selected_dofs);
+    
 				     /**
 				      * This function can be used when
 				      * different variables shall be
diff --git a/deal.II/deal.II/source/dofs/dof_tools.cc b/deal.II/deal.II/source/dofs/dof_tools.cc
index dc8c1768af..6fb8885849 100644
--- a/deal.II/deal.II/source/dofs/dof_tools.cc
+++ b/deal.II/deal.II/source/dofs/dof_tools.cc
@@ -711,6 +711,74 @@ DoFTools::extract_level_dofs(const unsigned int       level,
 
 
 
+#if deal_II_dimension != 1
+
+template <int dim>
+void
+DoFTools::extract_boundary_dofs (const DoFHandler<dim> &dof_handler,
+				 const vector<bool>    &component_select,
+				 vector<bool>          &selected_dofs)
+{
+  Assert (component_select.size() == dof_handler.get_fe().n_components(),
+	  ExcWrongSize (component_select.size(),
+			dof_handler.get_fe().n_components()));
+
+  selected_dofs.resize (dof_handler.n_dofs(), false);
+  vector<unsigned int> face_dof_indices (dof_handler.get_fe().dofs_per_face);
+  for (DoFHandler<dim>::active_cell_iterator cell=dof_handler.begin_active();
+       cell!=dof_handler.end(); ++cell)
+    for (unsigned int face=0; face<GeometryInfo<dim>::faces_per_cell; ++face)
+      if (cell->at_boundary(face))
+	{
+	  cell->face(face)->get_dof_indices (face_dof_indices);
+	  for (unsigned int i=0; i<dof_handler.get_fe().dofs_per_face; ++i)
+	    if (component_select[dof_handler.get_fe().
+				face_system_to_component_index(i).first] == true)
+	      selected_dofs[face_dof_indices[i]] = true;
+	};
+};
+
+
+#else
+
+template <>
+void
+DoFTools::extract_boundary_dofs (const DoFHandler<1> &dof_handler,
+				 const vector<bool>  &component_select,
+				 vector<bool>        &selected_dofs)
+{
+  Assert (component_select.size() == dof_handler.get_fe().n_components(),
+	  ExcWrongSize (component_select.size(),
+			dof_handler.get_fe().n_components()));
+	  
+  selected_dofs.resize (dof_handler.n_dofs(), false);
+
+  Assert (dof_handler.get_fe().dofs_per_face == dof_handler.get_fe().dofs_per_vertex,
+	  ExcInternalError());
+  
+				   // loop over coarse grid cells
+  for (DoFHandler<1>::cell_iterator cell=dof_handler.begin(0);
+       cell!=dof_handler.end(0); ++cell)
+    {
+				       // check left-most vertex
+      if (cell->neighbor(0) == dof_handler.end())
+	for (unsigned int i=0; i<dof_handler.get_fe().dofs_per_face; ++i)
+	  if (component_select[dof_handler.get_fe().
+			      face_system_to_component_index(i).first] == true)
+	    selected_dofs[cell->vertex_dof_index(0,i)] = true;
+				       // check right-most vertex
+      if (cell->neighbor(1) == dof_handler.end())
+	for (unsigned int i=0; i<dof_handler.get_fe().dofs_per_face; ++i)
+	  if (component_select[dof_handler.get_fe().
+			      face_system_to_component_index(i).first] == true)
+	    selected_dofs[cell->vertex_dof_index(1,i)] = true;
+    };
+};
+
+
+#endif
+
+
 
 template <int dim>
 void
@@ -1195,6 +1263,13 @@ template void DoFTools::extract_level_dofs(unsigned int level,
 					   const vector<bool>& local_select,
 					   vector<bool>& selected_dofs);
 
+#if deal_II_dimension != 1
+template
+void
+DoFTools::extract_boundary_dofs (const DoFHandler<deal_II_dimension> &,
+				 const vector<bool>                  &,
+				 vector<bool>                        &);
+#endif 
 
 template
 void
diff --git a/deal.II/doc/news/2000/c-3-0.html b/deal.II/doc/news/2000/c-3-0.html
index 4aa72144ea..965b934762 100644
--- a/deal.II/doc/news/2000/c-3-0.html
+++ b/deal.II/doc/news/2000/c-3-0.html
@@ -63,6 +63,10 @@
   estimates the norm of the gradient on each cell from finite
   difference approximations. 
 
+  <li> New: <code class="member">DoFTools::extract_boundary_dofs</code> 
+  finds all degrees of freedom which are at the boundary and belong to
+  specified components.
+
   <li> New: <code class="member">DoFTools::compute_intergrid_constraints</code> 
   allows to use different discretization grids for different variables.
 </ol>
-- 
2.39.5