From cd0146b15487a7f22e673fa30b0bb9bba1529600 Mon Sep 17 00:00:00 2001
From: bangerth <bangerth@0785d39b-7218-0410-832d-ea1e28bc413d>
Date: Tue, 7 Dec 2010 13:46:23 +0000
Subject: [PATCH] When codim=1, we can't take for granted that the left
 neighbor of the right neighbor is the current cell.

git-svn-id: https://svn.dealii.org/trunk@22937 0785d39b-7218-0410-832d-ea1e28bc413d
---
 .../deal.II/grid/tria_accessor.templates.h    | 19 +++++++------------
 deal.II/source/grid/tria_accessor.cc          | 14 ++++++++++++--
 2 files changed, 19 insertions(+), 14 deletions(-)

diff --git a/deal.II/include/deal.II/grid/tria_accessor.templates.h b/deal.II/include/deal.II/grid/tria_accessor.templates.h
index e9068436ac..6b95623667 100644
--- a/deal.II/include/deal.II/grid/tria_accessor.templates.h
+++ b/deal.II/include/deal.II/grid/tria_accessor.templates.h
@@ -2832,19 +2832,14 @@ inline
 unsigned int
 CellAccessor<dim,spacedim>::neighbor_face_no (const unsigned int neighbor) const
 {
-  if (dim==1)
-    return neighbor_of_neighbor(neighbor);
+  const unsigned int n2=neighbor_of_neighbor_internal(neighbor);
+  if (n2!=numbers::invalid_unsigned_int)
+				     // return this value as the
+				     // neighbor is not coarser
+    return n2;
   else
-    {
-      const unsigned int n2=neighbor_of_neighbor_internal(neighbor);
-      if (n2!=numbers::invalid_unsigned_int)
-					 // return this value as the
-					 // neighbor is not coarser
-	return n2;
-      else
-					 // the neighbor is coarser
-	return neighbor_of_coarser_neighbor(neighbor).first;
-    }
+				     // the neighbor is coarser
+    return neighbor_of_coarser_neighbor(neighbor).first;
 }
 
 DEAL_II_NAMESPACE_CLOSE
diff --git a/deal.II/source/grid/tria_accessor.cc b/deal.II/source/grid/tria_accessor.cc
index 376c94744f..00b028184c 100644
--- a/deal.II/source/grid/tria_accessor.cc
+++ b/deal.II/source/grid/tria_accessor.cc
@@ -1322,7 +1322,16 @@ unsigned int CellAccessor<dim,spacedim>::neighbor_of_neighbor_internal (const un
 {
   AssertIndexRange (neighbor, GeometryInfo<dim>::faces_per_cell);
 
-  if (dim==1)
+				   // if we have a 1d mesh in 1d, we
+				   // can assume that the left
+				   // neighbor of the right neigbor is
+				   // the current cell. but that is an
+				   // invariant that isn't true if the
+				   // mesh is embedded in a higher
+				   // dimensional space, so we have to
+				   // fall back onto the generic code
+				   // below
+  if ((dim==1) && (spacedim==dim))
     return GeometryInfo<dim>::opposite_face[neighbor];
 
   const TriaIterator<CellAccessor<dim, spacedim> > neighbor_cell = this->neighbor(neighbor);
@@ -1375,7 +1384,8 @@ template <int dim, int spacedim>
 unsigned int CellAccessor<dim,spacedim>::neighbor_of_neighbor (const unsigned int neighbor) const
 {
   const unsigned int n2=neighbor_of_neighbor_internal(neighbor);
-  Assert (n2!=numbers::invalid_unsigned_int, TriaAccessorExceptions::ExcNeighborIsCoarser());
+  Assert (n2!=numbers::invalid_unsigned_int,
+	  TriaAccessorExceptions::ExcNeighborIsCoarser());
 
   return n2;
 }
-- 
2.39.5