From: Peter Munch <peterrmuench@gmail.com>
Date: Fri, 1 Jul 2022 20:38:44 +0000 (+0200)
Subject: Be explicit regarding zero tolerance in merge_triangulations
X-Git-Tag: v9.5.0-rc1~1120^2
X-Git-Url: https://gitweb.dealii.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=bc078dfb0acd6e2530dca8ecb9d19352e25d9efc;p=dealii.git

Be explicit regarding zero tolerance in merge_triangulations
---

diff --git a/include/deal.II/grid/grid_generator.h b/include/deal.II/grid/grid_generator.h
index a0f20e4c7a..d6de5006ab 100644
--- a/include/deal.II/grid/grid_generator.h
+++ b/include/deal.II/grid/grid_generator.h
@@ -1864,7 +1864,7 @@ namespace GridGenerator
    * {
    *   double length = std::numeric_limits<double>::max();
    *   for (const auto &cell : tria.active_cell_iterators())
-   *     for (unsigned int n = 0; n < GeometryInfo<dim>::lines_per_cell; ++n)
+   *     for (const auto n : cell->line_indices())
    *       length = std::min(length, (cell->line(n)->vertex(0) -
    *                                  cell->line(n)->vertex(1)).norm());
    *   return length;
@@ -1875,7 +1875,7 @@ namespace GridGenerator
    * @endcode
    *
    * This will merge any vertices that are closer than any pair of vertices on
-   * the input meshes.
+   * the input meshes. If the tolerance is set to zero, vertices are not merged.
    *
    * @note The two input triangulations must be
    * @ref GlossCoarseMesh "coarse meshes",
diff --git a/include/deal.II/grid/grid_tools.h b/include/deal.II/grid/grid_tools.h
index 4ba5992256..5a0d816229 100644
--- a/include/deal.II/grid/grid_tools.h
+++ b/include/deal.II/grid/grid_tools.h
@@ -439,7 +439,8 @@ namespace GridTools
    * vertices.
    *
    * Two vertices are considered equal if their difference in each coordinate
-   * direction is less than @p tol.
+   * direction is less than @p tol. This implies that nothing happens if
+   * the tolerance is set to zero.
    */
   template <int dim, int spacedim>
   void
diff --git a/source/grid/grid_generator.cc b/source/grid/grid_generator.cc
index ebaaae4f0b..41fa3a00f4 100644
--- a/source/grid/grid_generator.cc
+++ b/source/grid/grid_generator.cc
@@ -6544,6 +6544,10 @@ namespace GridGenerator
       GridTools::consistently_order_cells(cells);
     result.clear();
     result.create_triangulation(vertices, cells, subcell_data);
+
+    Assert(duplicated_vertex_tolerance > 0.0 ||
+             n_accumulated_vertices == result.n_vertices(),
+           ExcInternalError());
   }
 
 
diff --git a/source/grid/grid_tools.cc b/source/grid/grid_tools.cc
index d8c3279452..f4549dfb95 100644
--- a/source/grid/grid_tools.cc
+++ b/source/grid/grid_tools.cc
@@ -744,6 +744,9 @@ namespace GridTools
                              std::vector<unsigned int> &   considered_vertices,
                              const double                  tol)
   {
+    if (tol == 0.0)
+      return; // nothing to do per definition
+
     AssertIndexRange(2, vertices.size());
     std::vector<unsigned int> new_vertex_numbers(vertices.size());
     std::iota(new_vertex_numbers.begin(), new_vertex_numbers.end(), 0);