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 b328ca0fd2475d002e73fe33d90ec0151d116956..97e7977728a1ce5c8e35bc68c741d371396af375 100644 (file)
--- 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