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git-svn-id: https://svn.dealii.org/trunk@21307 0785d39b-7218-0410-832d-ea1e28bc413d

diff --git a/deal.II/examples/step-45/step-45.cc b/deal.II/examples/step-45/step-45.cc
index bc52cf6793ab51e5f3c4d39832e8e4422cbe671e..be9ef9cba57966ee0db5c118326b420905e4d60c 100644 (file)
--- a/deal.II/examples/step-45/step-45.cc
+++ b/deal.II/examples/step-45/step-45.cc
@@ -59,7 +59,9 @@ using namespace dealii;
                                 // will hold the constraints from the
                                 // periodic boundary condition. We will
                                 // initialize it in the
-                                // <code>setup_system()</code> function.
+                                // <code>make_periodicity_constraints()</code>
+                                // function which we call from
+                                // <code>make_grid_and_dofs()</code>.
 class LaplaceProblem
 {
   public:
@@ -82,6 +84,7 @@ class LaplaceProblem
     void assemble_system ();
     void output_results ();
     void make_grid_and_dofs ();
+    void make_periodicity_constraints ();
     void solve ();   
 };
 
@@ -130,6 +133,8 @@ LaplaceProblem::LaplaceProblem ()
 {}
 
 
+                                 // @sect4{LaplaceProblem::make_grid_and_dofs}
+
 void LaplaceProblem::make_grid_and_dofs ()
 {
   GridGenerator::hyper_cube (triangulation);
@@ -265,6 +270,18 @@ void LaplaceProblem::make_grid_and_dofs ()
                                 // Assembling the system matrix and the
                                 // right-hand side vector is done as in other
                                 // tutorials before.
+                                //
+                                // The only difference here is that we don't
+                                // copy elements from local contributions
+                                // into the global matrix and later fix up
+                                // constrained degrees of freedom, but that
+                                // we let the ConstraintMatrix do this job in
+                                // one swoop for us using the
+                                // ConstraintMatrix::distribute_local_to_global
+                                // function(). This was previously already
+                                // demonstrated in step-16, step-22, for
+                                // example, along with a discussion in the
+                                // introduction of step-27.
 void LaplaceProblem::assemble_system ()
 {
   QGauss<2>  quadrature_formula(2);