From 127d9a4a4e66ae7dc2e4aba0769d8e7e79a6e59a Mon Sep 17 00:00:00 2001
From: Daniel Arndt <daniel.arndt@iwr.uni-heidelberg.de>
Date: Thu, 9 Aug 2018 11:21:02 +0200
Subject: [PATCH] Add test for level difference across periodic faces on serial
 Triangulations

---
 tests/grid/periodicity_01.cc     | 91 ++++++++++++++++++++++++++++++++
 tests/grid/periodicity_01.output |  3 ++
 2 files changed, 94 insertions(+)
 create mode 100644 tests/grid/periodicity_01.cc
 create mode 100644 tests/grid/periodicity_01.output

diff --git a/tests/grid/periodicity_01.cc b/tests/grid/periodicity_01.cc
new file mode 100644
index 0000000000..588e79f458
--- /dev/null
+++ b/tests/grid/periodicity_01.cc
@@ -0,0 +1,91 @@
+// ---------------------------------------------------------------------
+//
+// 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.md at
+// the top level directory of deal.II.
+//
+// ---------------------------------------------------------------------
+
+// Check that there is at most a one level difference between cells
+// across periodic boundary faces for serial Triangulations.
+
+#include <deal.II/base/geometry_info.h>
+
+#include <deal.II/grid/grid_generator.h>
+#include <deal.II/grid/grid_out.h>
+#include <deal.II/grid/grid_tools.h>
+#include <deal.II/grid/tria.h>
+#include <deal.II/grid/tria_accessor.h>
+#include <deal.II/grid/tria_iterator.h>
+
+#include "../tests.h"
+
+template <int dim>
+void
+test()
+{
+  double left  = -1.;
+  double right = 1.;
+
+  Triangulation<dim> tria;
+
+  GridGenerator::hyper_cube(tria, left, right, true);
+
+  // setup periodic boundary conditions
+  std::vector<
+    GridTools::PeriodicFacePair<typename Triangulation<dim>::cell_iterator>>
+    periodicity_vector;
+
+  // for the hypercube faces
+  unsigned int id1 = 0; // id of the left boundary
+  unsigned int id2 = 1; // id of the right boundary boundary
+  GridTools::collect_periodic_faces(
+    tria, id1, id2, /*x-direction*/ 0, periodicity_vector);
+
+  tria.add_periodicity(periodicity_vector);
+
+  const unsigned int n_refinements = 5;
+  const double       tolerance     = 1.e-3;
+
+  for (unsigned int n = 0; n < n_refinements; ++n)
+    {
+      for (const auto &cell : tria.active_cell_iterators())
+        if (cell->center()[0] > -tolerance)
+          cell->set_refine_flag();
+
+      tria.execute_coarsening_and_refinement();
+    }
+
+  // Let's check how many cells have a periodic neighbor.
+  unsigned int neighbor_count = 0;
+
+  for (const auto &cell : tria.active_cell_iterators())
+    for (unsigned int f = 0; f < GeometryInfo<2>::faces_per_cell; ++f)
+      if (cell->has_periodic_neighbor(f))
+        ++neighbor_count;
+
+  deallog << "Found " << neighbor_count << " faces with periodic neighbor"
+          << std::endl;
+
+  const unsigned int expected_neighbor_count =
+    Utilities::pow(2, (dim - 1) * (n_refinements - 1)) +
+    Utilities::pow(2, (dim - 1) * n_refinements);
+  AssertThrow(neighbor_count == expected_neighbor_count, ExcInternalError());
+}
+
+
+int
+main()
+{
+  initlog();
+  test<2>();
+  test<3>();
+  return 0;
+}
diff --git a/tests/grid/periodicity_01.output b/tests/grid/periodicity_01.output
new file mode 100644
index 0000000000..cf04d7bf87
--- /dev/null
+++ b/tests/grid/periodicity_01.output
@@ -0,0 +1,3 @@
+
+DEAL::Found 48 faces with periodic neighbor
+DEAL::Found 1280 faces with periodic neighbor
-- 
2.39.5