From: Wolfgang Bangerth <bangerth@math.tamu.edu>
Date: Sat, 1 Aug 2009 02:18:37 +0000 (+0000)
Subject: Make sure we back out of the steepest decent if the gradient is
X-Git-Tag: v8.0.0~7406
X-Git-Url: https://gitweb.dealii.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=e48d18a34af7c7188788ad8dc30f0674a96f76e7;p=dealii.git

Make sure we back out of the steepest decent if the gradient is
zero. This happens, for example, in bits/distorted_cells_06 without
this hunk.


git-svn-id: https://svn.dealii.org/trunk@19159 0785d39b-7218-0410-832d-ea1e28bc413d
---

diff --git a/deal.II/deal.II/source/grid/grid_tools.cc b/deal.II/deal.II/source/grid/grid_tools.cc
index b328ca0fd2..97e7977728 100644
--- a/deal.II/deal.II/source/grid/grid_tools.cc
+++ b/deal.II/deal.II/source/grid/grid_tools.cc
@@ -1541,6 +1541,18 @@ namespace internal
 		       step_length);
 	      }
 
+					     // sometimes, the
+					     // (unprojected) gradient
+					     // is perpendicular to
+					     // the manifold, but we
+					     // can't go there if
+					     // respect_manifold==true. in
+					     // that case, gradient=0,
+					     // and we simply need to
+					     // quite the loop here
+	    if (gradient.norm() == 0)
+	      break;
+	    
 					     // so we need to go in
 					     // direction -gradient. the
 					     // optimal value of the