Fix normal_vector crash for small cells

diff --git a/source/grid/manifold.cc b/source/grid/manifold.cc
index 6853c082b7ddf99cc1f7bdf7d1640a5d47463e9a..35d213df01a3e8bab23fbd459a087ad1361b8fbd 100644 (file)
--- a/source/grid/manifold.cc
+++ b/source/grid/manifold.cc
@@ -933,7 +933,16 @@ FlatManifold<dim, spacedim>::normal_vector(
                         "of what a deformed cell is. You may want to output "
                         "the vertices of your cell."));
 
-      if (delta_xi.norm() < eps)
+      // It turns out that the check in reference coordinates with an absolute
+      // tolerance can cause a convergence failure of the Newton method as
+      // seen in tests/manifold/flat_manifold_09.cc. To work around this, also
+      // use a convergence check in world coordinates. This check has to be
+      // relative to the size of the face of course. Here we decided to use
+      // diameter because it works for non-planar faces and is cheap to
+      // compute:
+      const double normalized_delta_world = (F - p).norm() / face->diameter();
+
+      if (delta_xi.norm() < eps || normalized_delta_world < eps)
         break;
     }
 

diff --git a/tests/manifold/flat_manifold_09.cc b/tests/manifold/flat_manifold_09.cc
new file mode 100644 (file)
index 0000000..c035ea4
--- /dev/null
+++ b/tests/manifold/flat_manifold_09.cc
@@ -0,0 +1,167 @@
+// ---------------------------------------------------------------------
+//
+// Copyright (C) 2018 by the deal.II authors
+//
+// This file is part of the deal.II library.
+//
+// The deal.II library is free software; you can use it, redistribute
+// it, and/or modify it under the terms of the GNU Lesser General
+// Public License as published by the Free Software Foundation; either
+// version 2.1 of the License, or (at your option) any later version.
+// The full text of the license can be found in the file LICENSE at
+// the top level of the deal.II distribution.
+//
+// ---------------------------------------------------------------------
+
+
+// Test that Manifold::get_normal_vector also works for very small cells (9+
+// refinement steps) instead of failing with
+//
+// "The Newton iteration to find the reference point did not converge in 10
+// iterations"
+
+// clang-format off
+/*
+Example output of a failing iteration:
+
+  1 delta_xi: 0.707107 xi: 1 1 F: 0.449978 0.159888 0 p: 0.45 0.159912 0 delta: 0.5
+  2 delta_xi: 1.26319e-12 xi: 1 1 F: 0.45 0.159912 0 p: 0.45 0.159912 0 delta: 8.45028e-13
+  3 delta_xi: 1.26319e-12 xi: 1 1 F: 0.45 0.159912 0 p: 0.45 0.159912 0 delta: 8.45028e-13
+  4 delta_xi: 1.26319e-12 xi: 1 1 F: 0.45 0.159912 0 p: 0.45 0.159912 0 delta: 8.45028e-13
+  5 delta_xi: 1.26319e-12 xi: 1 1 F: 0.45 0.159912 0 p: 0.45 0.159912 0 delta: 8.45028e-13
+  6 delta_xi: 1.26319e-12 xi: 1 1 F: 0.45 0.159912 0 p: 0.45 0.159912 0 delta: 8.45028e-13
+  7 delta_xi: 1.26319e-12 xi: 1 1 F: 0.45 0.159912 0 p: 0.45 0.159912 0 delta: 8.45028e-13
+  8 delta_xi: 1.26319e-12 xi: 1 1 F: 0.45 0.159912 0 p: 0.45 0.159912 0 delta: 8.45028e-13
+  9 delta_xi: 1.26319e-12 xi: 1 1 F: 0.45 0.159912 0 p: 0.45 0.159912 0 delta: 8.45028e-13
+  10 delta_xi: 1.26319e-12 xi: 1 1 F: 0.45 0.159912 0 p: 0.45 0.159912 0 delta: 8.45028e-13
+*/
+// clang-format on
+
+
+#include "../tests.h"
+
+
+// all include files you need here
+#include <deal.II/fe/fe_q.h>
+#include <deal.II/fe/fe_values.h>
+
+#include <deal.II/grid/grid_generator.h>
+#include <deal.II/grid/grid_out.h>
+#include <deal.II/grid/manifold_lib.h>
+#include <deal.II/grid/tria.h>
+#include <deal.II/grid/tria_accessor.h>
+#include <deal.II/grid/tria_iterator.h>
+
+template <int dim>
+void
+make_grid(Triangulation<dim> &triangulation)
+{
+  std::vector<std::vector<double>> spacing(3, std::vector<double>());
+
+  for (int i = 0; i < 5; ++i)
+    spacing[0].push_back(0.09);
+  spacing[0].push_back(0.1);
+  for (int i = 0; i < 10; ++i)
+    spacing[0].push_back(0.095);
+  for (int i = 0; i < 5; ++i)
+    spacing[0].push_back(0.2);
+
+  spacing[1].push_back(0.075);
+  spacing[1].push_back(0.075);
+  spacing[1].push_back(0.1);
+  spacing[1].push_back(0.08);
+  spacing[1].push_back(0.08);
+
+  const unsigned int z_slices = 4;
+  for (unsigned int z = 0; z < z_slices; ++z)
+    spacing[2].push_back(0.41 / z_slices);
+
+  Point<3>        p;
+  TableIndices<3> sizes;
+  sizes[0] = spacing[0].size();
+  sizes[1] = spacing[1].size();
+  sizes[2] = spacing[2].size();
+  Table<3, types::material_id> material_id;
+  material_id.TableBase<3, types::material_id>::reinit(sizes);
+
+  for (unsigned int z = 0; z < z_slices; ++z)
+    material_id(5, 2, z) = -1;
+
+  GridGenerator::subdivided_hyper_rectangle(
+    triangulation, spacing, p, material_id, false);
+}
+
+template <int dim>
+void
+check(Triangulation<dim> &tria)
+{
+  FE_Q<dim> fe(2);
+
+  Quadrature<dim - 1> quadrature_formula(fe.get_unit_face_support_points());
+
+  FEFaceValues<dim> fe_face_values(
+    fe, quadrature_formula, update_normal_vectors | update_quadrature_points);
+
+  Tensor<1, dim> n;
+  for (const auto &cell : tria.active_cell_iterators())
+    {
+      for (unsigned int face = 0; face < GeometryInfo<dim>::faces_per_cell;
+           ++face)
+        if (cell->face(face)->at_boundary())
+          {
+            fe_face_values.reinit(cell, face);
+            for (unsigned int q_point = 0; q_point < quadrature_formula.size();
+                 ++q_point)
+              n += (cell->face(face)->get_manifold().normal_vector(
+                cell->face(face), fe_face_values.quadrature_point(q_point)));
+          }
+    }
+  std::cout << n << std::endl;
+}
+
+template <int dim>
+void
+test()
+{
+  Triangulation<dim> tria;
+  make_grid(tria);
+  tria.refine_global(1);
+
+
+  Point<dim> p;
+  p(0) = 0.45;
+  p(1) = 0.16;
+  for (unsigned int step = 0; step < 10; ++step)
+    {
+      std::cout << "step " << step << std::endl;
+      for (auto cell : tria.active_cell_iterators())
+        {
+          for (unsigned int v = 0; v < GeometryInfo<dim>::vertices_per_cell;
+               ++v)
+            {
+              if (p.distance(cell->vertex(v)) < 0.03 / (1 << step))
+                {
+                  cell->set_refine_flag();
+                  break;
+                }
+            }
+        }
+
+      tria.execute_coarsening_and_refinement();
+
+      check(tria);
+    }
+
+
+  deallog << "OK" << std::endl;
+}
+
+int
+main()
+{
+  initlog();
+
+
+  test<3>();
+  return 0;
+}

diff --git a/tests/manifold/flat_manifold_09.output b/tests/manifold/flat_manifold_09.output
new file mode 100644 (file)
index 0000000..0fd8fc1
--- /dev/null
+++ b/tests/manifold/flat_manifold_09.output
@@ -0,0 +1,2 @@
+
+DEAL::OK