From 28d8f3cb4107242efe489212776a290a3b0a4341 Mon Sep 17 00:00:00 2001
From: Wolfgang Bangerth <bangerth@math.tamu.edu>
Date: Wed, 1 Jul 2015 11:20:54 -0500
Subject: [PATCH] Add a declared but not implemented function.

This addresses a linker error recently posted to the mailing list. The issue
is that we have iterators that represent faces of cells and a specialization
for the faces of 1d cells, i.e., vertices. These class specializations have
most of the regular accessor members declared, but here is one that was
declared without being defined.

This patch adds a definition of the function. The issue is relatively
uncritical since the so-defined function does not actually have to do
anything other than return an invalid object (vertices have no children).
---
 doc/news/changes.h                            |  8 ++++++++
 include/deal.II/dofs/dof_accessor.h           |  6 ++++--
 include/deal.II/dofs/dof_accessor.templates.h | 12 ++++++++++++
 3 files changed, 24 insertions(+), 2 deletions(-)

diff --git a/doc/news/changes.h b/doc/news/changes.h
index 8f0c051b50..b1dc8ddad2 100644
--- a/doc/news/changes.h
+++ b/doc/news/changes.h
@@ -532,6 +532,14 @@ inconvenience this causes.
 <h3>Specific improvements</h3>
 
 <ol>
+  <li> Fixed: The specialization of DoFAccessor for zero-dimensional objects,
+  i.e., for vertices as created by accessing the faces of one-dimensional
+  cells, had a member function DoFAccessor::child() that was declared but not
+  implemented. This is now fixed.
+  <br>
+  (Wolfgang Bangerth,  2015/07/01)
+  </li>
+
   <li> Improved: Functions::Monomial::gradient function now works when both base and exponent
   are equal to zero for one or more components of the monomial.
   Also, an assertion is added to avoid exponentiation of negative base numbers with real exponents.
diff --git a/include/deal.II/dofs/dof_accessor.h b/include/deal.II/dofs/dof_accessor.h
index 89b7cf4e28..89ee601037 100644
--- a/include/deal.II/dofs/dof_accessor.h
+++ b/include/deal.II/dofs/dof_accessor.h
@@ -294,7 +294,7 @@ public:
    */
 
   /**
-   * Return an iterator pointing to the the @p c-th child.
+   * Return an iterator pointing to the @p c-th child.
    */
   TriaIterator<DoFAccessor<structdim,DH, level_dof_access> >
   child (const unsigned int c) const;
@@ -798,7 +798,9 @@ public:
    */
 
   /**
-   * Return an iterator pointing to the the @p c-th child.
+   * Return an invalid iterator of a type that represents pointing to a child
+   * of the current object. The object is invalid because points (as represented
+   * by the current class) do not have children.
    */
   TriaIterator<DoFAccessor<0,DH<1,spacedim>, level_dof_access > >
   child (const unsigned int c) const;
diff --git a/include/deal.II/dofs/dof_accessor.templates.h b/include/deal.II/dofs/dof_accessor.templates.h
index 0585f22126..cd691524bb 100644
--- a/include/deal.II/dofs/dof_accessor.templates.h
+++ b/include/deal.II/dofs/dof_accessor.templates.h
@@ -2325,6 +2325,18 @@ DoFAccessor<0,DH<1,spacedim>, level_dof_access>::operator != (const DoFAccessor<
 
 
 
+template <template <int, int> class DH, int spacedim, bool level_dof_access>
+inline
+TriaIterator<DoFAccessor<0,DH<1,spacedim>, level_dof_access > >
+DoFAccessor<0,DH<1,spacedim>, level_dof_access>::child (const unsigned int i) const
+{
+  return TriaIterator<DoFAccessor<0,DH<1,spacedim>, level_dof_access > >();
+}
+
+
+
+
+
 /*------------------------- Functions: DoFCellAccessor -----------------------*/
 
 
-- 
2.39.5