Terminate a loop in a timely manner.

In StraightBoundary::normal_vector(), we currently have a loop that could run
forever. This is not useful. Rather, terminate it after at most 10 iterations
and if it fails output some guidance to what the reason may be.

diff --git a/source/grid/tria_boundary.cc b/source/grid/tria_boundary.cc
index d7fae946ecd4e044816c51b2f83979098c5bccb8..61c0ea8f5e395c3b682735fee0184050ff3159d8 100644 (file)
--- a/source/grid/tria_boundary.cc
+++ b/source/grid/tria_boundary.cc
@@ -1,6 +1,6 @@
 // ---------------------------------------------------------------------
 //
-// Copyright (C) 1998 - 2014 by the deal.II authors
+// Copyright (C) 1998 - 2015 by the deal.II authors
 //
 // This file is part of the deal.II library.
 //
@@ -604,6 +604,7 @@ normal_vector (const typename Triangulation<dim,spacedim>::face_iterator &face,
 
   const double eps = 1e-12;
   Tensor<1,spacedim> grad_F[facedim];
+  unsigned int iteration = 0;
   while (true)
     {
       Point<spacedim> F;
@@ -630,6 +631,14 @@ normal_vector (const typename Triangulation<dim,spacedim>::face_iterator &face,
 
       const Point<facedim> delta_xi = -invert(H) * J;
       xi += delta_xi;
+      ++iteration;
+
+      Assert (iteration<10,
+              ExcMessage("The Newton iteration to find the reference point "
+                         "did not converge in 10 iterations. Do you have a "
+                         "deformed cell? (See the glossary for a definition "
+                         "of what a deformed cell is. You may want to output "
+                         "the vertices of your cell."));
 
       if (delta_xi.norm() < eps)
         break;