From: Daniel Arndt <daniel.arndt@iwr.uni-heidelberg.de>
Date: Wed, 1 Aug 2018 18:07:17 +0000 (+0200)
Subject: Allow merging multiple Triangulation objects at once
X-Git-Tag: v9.1.0-rc1~851^2~3
X-Git-Url: https://gitweb.dealii.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=fd8a21a6a7a68730e0d41c8ceb6a16f1304fb7f2;p=dealii.git

Allow merging multiple Triangulation objects at once
---

diff --git a/doc/news/changes/minor/20180801DanielArndt b/doc/news/changes/minor/20180801DanielArndt
new file mode 100644
index 0000000000..f29df0e876
--- /dev/null
+++ b/doc/news/changes/minor/20180801DanielArndt
@@ -0,0 +1,4 @@
+New: GridGenerator::merge_triangulations can merge multiple 
+Triangulation objects at once.
+<br>
+(Daniel Arndt, 2018/08/01)
diff --git a/include/deal.II/grid/grid_generator.h b/include/deal.II/grid/grid_generator.h
index 56da7be560..a96ad98b0d 100644
--- a/include/deal.II/grid/grid_generator.h
+++ b/include/deal.II/grid/grid_generator.h
@@ -1164,6 +1164,18 @@ namespace GridGenerator
                        const double duplicated_vertex_tolerance = 1.0e-12,
                        const bool   copy_manifold_ids           = false);
 
+  /**
+   * Same as above but allows to merge more than two triangulations at once.
+   */
+  template <int dim, int spacedim>
+  void
+  merge_triangulations(
+    const std::initializer_list<const Triangulation<dim, spacedim> *const>
+                                  triangulations,
+    Triangulation<dim, spacedim> &result,
+    const double                  duplicated_vertex_tolerance = 1.0e-12,
+    const bool                    copy_manifold_ids           = false);
+
   /**
    * Given the two triangulations specified as the first two arguments, create
    * the triangulation that contains the finest cells of both triangulation
diff --git a/source/grid/grid_generator.cc b/source/grid/grid_generator.cc
index e868b93980..50d0cb86fc 100644
--- a/source/grid/grid_generator.cc
+++ b/source/grid/grid_generator.cc
@@ -4139,61 +4139,55 @@ namespace GridGenerator
 
   template <int dim, int spacedim>
   void
-  merge_triangulations(const Triangulation<dim, spacedim> &triangulation_1,
-                       const Triangulation<dim, spacedim> &triangulation_2,
-                       Triangulation<dim, spacedim> &      result,
-                       const double duplicated_vertex_tolerance,
-                       const bool   copy_manifold_ids)
+  merge_triangulations(
+    const std::initializer_list<const Triangulation<dim, spacedim> *const>
+                                  triangulations,
+    Triangulation<dim, spacedim> &result,
+    const double                  duplicated_vertex_tolerance,
+    const bool                    copy_manifold_ids)
   {
-    // if either Triangulation is empty then merging is just a copy.
-    if (triangulation_1.n_cells() == 0)
-      {
-        result.copy_triangulation(triangulation_2);
-        return;
-      }
-    if (triangulation_2.n_cells() == 0)
+    for (const auto triangulation : triangulations)
       {
-        result.copy_triangulation(triangulation_1);
-        return;
+        (void)triangulation;
+        Assert(triangulation->n_levels() == 1,
+               ExcMessage("The input triangulations must be non-empty "
+                          "and must not be refined."));
       }
 
-    Assert(triangulation_1.n_levels() == 1,
-           ExcMessage("The input triangulations must be non-empty "
-                      "and must not be refined."));
-    Assert(triangulation_2.n_levels() == 1,
-           ExcMessage("The input triangulations must be non-empty "
-                      "and must not be refined."));
-
     // get the union of the set of vertices
-    std::vector<Point<spacedim>> vertices = triangulation_1.get_vertices();
-    vertices.insert(vertices.end(),
-                    triangulation_2.get_vertices().begin(),
-                    triangulation_2.get_vertices().end());
+    unsigned int n_vertices = 0;
+    for (const auto triangulation : triangulations)
+      n_vertices += triangulation->n_vertices();
+
+    std::vector<Point<spacedim>> vertices;
+    vertices.reserve(n_vertices);
+    for (const auto triangulation : triangulations)
+      vertices.insert(vertices.end(),
+                      triangulation->get_vertices().begin(),
+                      triangulation->get_vertices().end());
 
     // now form the union of the set of cells
     std::vector<CellData<dim>> cells;
-    cells.reserve(triangulation_1.n_cells() + triangulation_2.n_cells());
-    for (const auto &cell : triangulation_1.cell_iterators())
-      {
-        CellData<dim> this_cell;
-        for (unsigned int v = 0; v < GeometryInfo<dim>::vertices_per_cell; ++v)
-          this_cell.vertices[v] = cell->vertex_index(v);
-        this_cell.material_id = cell->material_id();
-        this_cell.manifold_id = cell->manifold_id();
-        cells.push_back(std::move(this_cell));
-      }
+    unsigned int               n_cells = 0;
+    for (const auto triangulation : triangulations)
+      n_cells += triangulation->n_cells();
 
-    // now do the same for the other other mesh. note that we have to
-    // translate the vertex indices
-    for (const auto &cell : triangulation_2.cell_iterators())
+    cells.reserve(n_cells);
+    unsigned int n_accumulated_vertices = 0;
+    for (const auto triangulation : triangulations)
       {
-        CellData<dim> this_cell;
-        for (unsigned int v = 0; v < GeometryInfo<dim>::vertices_per_cell; ++v)
-          this_cell.vertices[v] =
-            cell->vertex_index(v) + triangulation_1.n_vertices();
-        this_cell.material_id = cell->material_id();
-        this_cell.manifold_id = cell->manifold_id();
-        cells.push_back(std::move(this_cell));
+        for (const auto &cell : triangulation->cell_iterators())
+          {
+            CellData<dim> this_cell;
+            for (unsigned int v = 0; v < GeometryInfo<dim>::vertices_per_cell;
+                 ++v)
+              this_cell.vertices[v] =
+                cell->vertex_index(v) + n_accumulated_vertices;
+            this_cell.material_id = cell->material_id();
+            this_cell.manifold_id = cell->manifold_id();
+            cells.push_back(std::move(this_cell));
+          }
+        n_accumulated_vertices += triangulation->n_vertices();
       }
 
     // Now for the SubCellData
@@ -4207,8 +4201,11 @@ namespace GridGenerator
 
             case 2:
               {
-                subcell_data.boundary_lines.reserve(triangulation_1.n_lines() +
-                                                    triangulation_2.n_lines());
+                unsigned int n_boundary_lines = 0;
+                for (const auto triangulation : triangulations)
+                  n_boundary_lines += triangulation->n_lines();
+
+                subcell_data.boundary_lines.reserve(n_boundary_lines);
 
                 auto copy_line_manifold_ids =
                   [&](const Triangulation<dim, spacedim> &tria,
@@ -4230,23 +4227,28 @@ namespace GridGenerator
                         }
                   };
 
-                copy_line_manifold_ids(triangulation_1, 0);
-                copy_line_manifold_ids(triangulation_2,
-                                       triangulation_1.n_vertices());
+                unsigned int n_accumulated_vertices = 0;
+                for (const auto triangulation : triangulations)
+                  {
+                    copy_line_manifold_ids(*triangulation,
+                                           n_accumulated_vertices);
+                    n_accumulated_vertices += triangulation->n_vertices();
+                  }
                 break;
               }
 
             case 3:
               {
-                subcell_data.boundary_quads.reserve(triangulation_1.n_quads() +
-                                                    triangulation_2.n_quads());
+                unsigned int n_boundary_quads = 0;
+                for (const auto triangulation : triangulations)
+                  n_boundary_quads += triangulation->n_quads();
+
+                subcell_data.boundary_quads.reserve(n_boundary_quads);
                 // we can't do better here than to loop over all the lines
-                // bounding a face. For regular meshes an (interior) line in 3D
-                // is part of four cells. So this should be an appropriate
+                // bounding a face. For regular meshes an (interior) line in
+                // 3D is part of four cells. So this should be an appropriate
                 // guess.
-                subcell_data.boundary_lines.reserve(
-                  triangulation_1.n_cells() * 4 +
-                  triangulation_2.n_cells() * 4);
+                subcell_data.boundary_lines.reserve(4 * n_boundary_quads);
 
                 auto copy_face_and_line_manifold_ids =
                   [&](const Triangulation<dim, spacedim> &tria,
@@ -4287,10 +4289,13 @@ namespace GridGenerator
                               boundary_line); // trivially_copyable
                           }
                   };
-
-                copy_face_and_line_manifold_ids(triangulation_1, 0);
-                copy_face_and_line_manifold_ids(triangulation_2,
-                                                triangulation_1.n_vertices());
+                unsigned int n_accumulated_vertices = 0;
+                for (const auto triangulation : triangulations)
+                  {
+                    copy_face_and_line_manifold_ids(*triangulation,
+                                                    n_accumulated_vertices);
+                    n_accumulated_vertices += triangulation->n_vertices();
+                  }
                 break;
               }
             default:
@@ -4298,14 +4303,19 @@ namespace GridGenerator
           }
       }
 
-    // throw out duplicated vertices from the two meshes, reorder vertices as
-    // necessary and create the triangulation
-    std::vector<unsigned int> considered_vertices;
-    GridTools::delete_duplicated_vertices(vertices,
-                                          cells,
-                                          subcell_data,
-                                          considered_vertices,
-                                          duplicated_vertex_tolerance);
+    // throw out duplicated vertices
+    // since GridTools::delete_duplicated_vertices can only consider
+    // one duplications at once, we have to call the function one time less
+    // than the number of Triangulation objects to be merged.
+    for (unsigned int i = 0; i < triangulations.size(); ++i)
+      {
+        std::vector<unsigned int> considered_vertices;
+        GridTools::delete_duplicated_vertices(vertices,
+                                              cells,
+                                              subcell_data,
+                                              considered_vertices,
+                                              duplicated_vertex_tolerance);
+      }
 
     // reorder the cells to ensure that they satisfy the convention for
     // edge and face directions
@@ -4315,6 +4325,34 @@ namespace GridGenerator
   }
 
 
+
+  template <int dim, int spacedim>
+  void
+  merge_triangulations(const Triangulation<dim, spacedim> &triangulation_1,
+                       const Triangulation<dim, spacedim> &triangulation_2,
+                       Triangulation<dim, spacedim> &      result,
+                       const double duplicated_vertex_tolerance,
+                       const bool   copy_manifold_ids)
+  {
+    // if either Triangulation is empty then merging is just a copy.
+    if (triangulation_1.n_cells() == 0)
+      {
+        result.copy_triangulation(triangulation_2);
+        return;
+      }
+    if (triangulation_2.n_cells() == 0)
+      {
+        result.copy_triangulation(triangulation_1);
+        return;
+      }
+    merge_triangulations({&triangulation_1, &triangulation_2},
+                         result,
+                         duplicated_vertex_tolerance,
+                         copy_manifold_ids);
+  }
+
+
+
   template <int dim, int spacedim>
   void
   create_union_triangulation(
diff --git a/source/grid/grid_generator.inst.in b/source/grid/grid_generator.inst.in
index 6ac4262276..659485982f 100644
--- a/source/grid/grid_generator.inst.in
+++ b/source/grid/grid_generator.inst.in
@@ -69,6 +69,15 @@ for (deal_II_dimension : DIMENSIONS; deal_II_space_dimension : SPACE_DIMENSIONS)
         Triangulation<deal_II_dimension, deal_II_space_dimension> &,
         const std::vector<unsigned int> &);
 
+      template void
+      merge_triangulations(
+        const std::initializer_list<
+          const Triangulation<deal_II_dimension, deal_II_space_dimension>
+            *const> triangulations,
+        Triangulation<deal_II_dimension, deal_II_space_dimension> &result,
+        const double duplicated_vertex_tolerance = 1.0e-12,
+        const bool   copy_manifold_ids           = false);
+
       template void
       merge_triangulations(
         const Triangulation<deal_II_dimension, deal_II_space_dimension>
diff --git a/tests/grid/merge_triangulations_06.cc b/tests/grid/merge_triangulations_06.cc
new file mode 100644
index 0000000000..4b046796bb
--- /dev/null
+++ b/tests/grid/merge_triangulations_06.cc
@@ -0,0 +1,171 @@
+// ---------------------------------------------------------------------
+//
+// 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.
+//
+// ---------------------------------------------------------------------
+
+
+
+#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"
+
+
+// Test the version of GridTools::merge_triangulations that takes a
+// std::initializer_list.
+
+void
+test_2d()
+{
+  constexpr int      dim = 2;
+  Triangulation<dim> tria_1;
+  {
+    GridGenerator::hyper_cube(tria_1);
+    Tensor<1, dim> shift_vector;
+    shift_vector[0] = -1.;
+    shift_vector[1] = -1.;
+    GridTools::shift(shift_vector, tria_1);
+  }
+
+  Triangulation<dim> tria_2;
+  {
+    GridGenerator::hyper_cube(tria_2);
+    Tensor<1, dim> shift_vector;
+    shift_vector[1] = -1.;
+    GridTools::shift(shift_vector, tria_2);
+  }
+
+  Triangulation<dim> tria_3;
+  {
+    GridGenerator::hyper_cube(tria_3);
+    Tensor<1, dim> shift_vector;
+    shift_vector[0] = -1.;
+    GridTools::shift(shift_vector, tria_3);
+  }
+
+  Triangulation<dim> tria_4;
+  {
+    GridGenerator::hyper_cube(tria_4);
+  }
+
+  // now merge triangulations
+  Triangulation<dim> result;
+  GridGenerator::merge_triangulations({&tria_1, &tria_2, &tria_3, &tria_4},
+                                      result);
+
+  GridOut().write_gnuplot(result, deallog.get_file_stream());
+
+  deallog << "     Total number of cells        = " << result.n_cells()
+          << std::endl
+          << "     Total number of vertices = " << result.n_used_vertices()
+          << std::endl;
+}
+
+void
+test_3d()
+{
+  constexpr int      dim = 3;
+  Triangulation<dim> tria_1;
+  {
+    GridGenerator::hyper_cube(tria_1);
+    Tensor<1, dim> shift_vector;
+    shift_vector[0] = -1.;
+    shift_vector[1] = -1.;
+    shift_vector[2] = -1.;
+    GridTools::shift(shift_vector, tria_1);
+  }
+
+  Triangulation<dim> tria_2;
+  {
+    GridGenerator::hyper_cube(tria_2);
+    Tensor<1, dim> shift_vector;
+    shift_vector[1] = -1.;
+    shift_vector[2] = -1.;
+    GridTools::shift(shift_vector, tria_2);
+  }
+
+  Triangulation<dim> tria_3;
+  {
+    GridGenerator::hyper_cube(tria_3);
+    Tensor<1, dim> shift_vector;
+    shift_vector[0] = -1.;
+    shift_vector[2] = -1.;
+    GridTools::shift(shift_vector, tria_3);
+  }
+
+  Triangulation<dim> tria_4;
+  {
+    Tensor<1, dim> shift_vector;
+    shift_vector[2] = -1.;
+    GridGenerator::hyper_cube(tria_4);
+    GridTools::shift(shift_vector, tria_4);
+  }
+
+  Triangulation<dim> tria_5;
+  {
+    GridGenerator::hyper_cube(tria_5);
+    Tensor<1, dim> shift_vector;
+    shift_vector[0] = -1.;
+    shift_vector[1] = -1.;
+    GridTools::shift(shift_vector, tria_5);
+  }
+
+  Triangulation<dim> tria_6;
+  {
+    GridGenerator::hyper_cube(tria_6);
+    Tensor<1, dim> shift_vector;
+    shift_vector[1] = -1.;
+    GridTools::shift(shift_vector, tria_6);
+  }
+
+  Triangulation<dim> tria_7;
+  {
+    GridGenerator::hyper_cube(tria_7);
+    Tensor<1, dim> shift_vector;
+    shift_vector[0] = -1.;
+    GridTools::shift(shift_vector, tria_7);
+  }
+
+  Triangulation<dim> tria_8;
+  {
+    GridGenerator::hyper_cube(tria_8);
+  }
+
+  // now merge triangulations
+  Triangulation<dim> result;
+  GridGenerator::merge_triangulations(
+    {&tria_1, &tria_2, &tria_3, &tria_4, &tria_5, &tria_6, &tria_7, &tria_8},
+    result);
+
+  GridOut().write_gnuplot(result, deallog.get_file_stream());
+
+  deallog << "     Total number of cells        = " << result.n_cells()
+          << std::endl
+          << "     Total number of vertices = " << result.n_used_vertices()
+          << std::endl;
+}
+
+int
+main()
+{
+  initlog();
+
+  test_2d();
+  test_3d();
+
+  return 0;
+}
diff --git a/tests/grid/merge_triangulations_06.output b/tests/grid/merge_triangulations_06.output
new file mode 100644
index 0000000000..3248035357
--- /dev/null
+++ b/tests/grid/merge_triangulations_06.output
@@ -0,0 +1,225 @@
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+DEAL::     Total number of cells        = 8
+DEAL::     Total number of vertices = 27