From: Martin Kronbichler <kronbichler@lnm.mw.tum.de>
Date: Mon, 23 Feb 2015 14:29:36 +0000 (+0100)
Subject: Comment on the behavior of FE_TraceQ as compared to FE_Q.
X-Git-Tag: v8.3.0-rc1~430^2
X-Git-Url: https://gitweb.dealii.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=2da2ffd863848b59eba0b8aa4fff1cc6f3d6150d;p=dealii.git

Comment on the behavior of FE_TraceQ as compared to FE_Q.
---

diff --git a/include/deal.II/fe/fe_trace.h b/include/deal.II/fe/fe_trace.h
index 48c3fd8ffe..757d30a6e8 100644
--- a/include/deal.II/fe/fe_trace.h
+++ b/include/deal.II/fe/fe_trace.h
@@ -40,8 +40,6 @@ DEAL_II_NAMESPACE_OPEN
  *
  * @todo Polynomials::LagrangeEquidistant should be and will be replaced by
  * Polynomials::LagrangeGaussLobatto as soon as such a polynomial set exists.
- * @todo so far, hanging nodes are not implemented
- *
  */
 
 template <int dim, int spacedim=dim>
@@ -55,6 +53,11 @@ public:
    */
   FE_TraceQ(unsigned int p);
 
+  /**
+   * @p clone function instead of a copy constructor.
+   *
+   * This function is needed by the constructors of @p FESystem.
+   */
   virtual FiniteElement<dim,spacedim> *clone() const;
 
   /**
@@ -78,9 +81,6 @@ public:
   virtual std::pair<Table<2,bool>, std::vector<unsigned int> >
   get_constant_modes () const;
 
-
-
-
   /**
    * Return whether this element implements its hanging node constraints in
    * the new way, which has to be used to make elements "hp compatible".
@@ -130,6 +130,7 @@ private:
    * Store a copy of FE_Q for delegating the hp-constraints functionality.
    */
   FE_Q<dim, spacedim> fe_q;
+
   /**
    * Return vector with dofs per vertex, line, quad, hex.
    */
diff --git a/source/fe/fe_trace.cc b/source/fe/fe_trace.cc
index 4d5306fbc2..0acd179ef7 100644
--- a/source/fe/fe_trace.cc
+++ b/source/fe/fe_trace.cc
@@ -68,12 +68,9 @@ template <int dim, int spacedim>
 std::string
 FE_TraceQ<dim,spacedim>::get_name () const
 {
-  // note that the
-  // FETools::get_fe_from_name
-  // function depends on the
-  // particular format of the string
-  // this function returns, so they
-  // have to be kept in synch
+  // note that the FETools::get_fe_from_name function depends on the
+  // particular format of the string this function returns, so they have to be
+  // kept in synch
 
   std::ostringstream namebuf;
   namebuf << "FE_TraceQ<"
@@ -95,6 +92,11 @@ FE_TraceQ<dim,spacedim>::has_support_on_face (const unsigned int shape_index,
   Assert (face_index < GeometryInfo<dim>::faces_per_cell,
           ExcIndexRange (face_index, 0, GeometryInfo<dim>::faces_per_cell));
 
+  // FE_TraceQ shares the numbering of elemental degrees of freedom with FE_Q
+  // except for the missing interior ones (quad dofs in 2D and hex dofs in
+  // 3D). Therefore, it is safe to ask fe_q for the corresponding
+  // information. The assertion 'shape_index < this->dofs_per_cell' will make
+  // sure that we only access the trace dofs.
   return fe_q.has_support_on_face (shape_index, face_index);
 }
 
@@ -117,6 +119,9 @@ template <int dim, int spacedim>
 std::vector<unsigned int>
 FE_TraceQ<dim,spacedim>::get_dpo_vector (const unsigned int deg)
 {
+  // This constructs FE_TraceQ in exactly the same way as FE_Q except for the
+  // interior degrees of freedom that are not present here (lnine in 1D, quad
+  // in 2D, hex in 3D).
   AssertThrow(deg>0,ExcMessage("FE_TraceQ needs to be of degree > 0."));
   std::vector<unsigned int> dpo(dim+1, 1U);
   dpo[dim]=0;