From: Timo Heister <timo.heister@gmail.com>
Date: Sat, 7 Sep 2024 00:53:47 +0000 (-0400)
Subject: address comments
X-Git-Url: https://gitweb.dealii.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=refs%2Fpull%2F17639%2Fhead;p=dealii.git

address comments
---

diff --git a/include/deal.II/grid/grid_generator.h b/include/deal.II/grid/grid_generator.h
index 6acc16bbab..90f9c9fa98 100644
--- a/include/deal.II/grid/grid_generator.h
+++ b/include/deal.II/grid/grid_generator.h
@@ -2429,20 +2429,20 @@ namespace GridGenerator
    * Perform an Alfeld split (also called barycentric refinement) of a simplex
    * mesh.
    *
-   * @note Currently only implemented for @p dim = 2.
-
-   * This function takes a simplex mesh (@p in_tria) and subdivides each
-   * triangle into three triangles with a single new vertex (the barycenter). In
-   * the process, the simplex mesh is flattened (no hierarchy is kept).
+   * Each simplex cell in the input mesh (given in @p in_tria) is refined into
+   * three (for @p dim = 2) or four (for @p dim = 3) simplices connecting to the
+   * barycenter, which is the only new vertex added for each input cell. In the
+   * process, the simplex mesh is flattened (no hierarchy is kept).
+   *
+   * @note Currently only implemented for @p dim = 2 and hanging nodes are not
+   * supported.
    *
    * @image html alfeld-split.svg
    *
    * The meshes produced by this function can be used for Scott-Vogelius
-   elements
-   * for the Stokes equation: The $P_k - DGP_{k-1}$ element is point-wise
-   divergence
-   * free on barycentric refined meshes for $k\geq 2$ for @p dim = 2 and $k\geq 3$
-   * for @p dim = 3, see @cite Farrell2021.
+   * elements for the Stokes equation: The $P_k - DGP_{k-1}$ element is
+   * point-wise divergence free on barycentric refined meshes for $k\geq 2$
+   * for @p dim = 2 and $k\geq 3$ for @p dim = 3, see @cite Farrell2021.
    *
    * Also see
    * @ref simplex "Simplex support".
diff --git a/source/grid/grid_generator.cc b/source/grid/grid_generator.cc
index 2c483da6e4..6ece144599 100644
--- a/source/grid/grid_generator.cc
+++ b/source/grid/grid_generator.cc
@@ -8423,16 +8423,12 @@ namespace GridGenerator
     static const ndarray<unsigned int, 3, 3> table_2D_cell = {
       {{{0, 1, 3}}, {{1, 2, 3}}, {{2, 0, 3}}}};
 
-    /* Boundary-faces 2d:
-     * After converting, each of the 4 quadrilateral faces is defined by faces
-     * of 2 different triangles, i.e., lines. Note that lines are defined by 2
-     * vertices.
-     */
+    // Boundary-faces 2d:
+    // Each face of the original simplex is defined by the following vertices:
     static const ndarray<unsigned int, 4, 2, 2>
       vertex_ids_for_boundary_faces_2d = {
         {{{{{0, 1}}}}, {{{{1, 2}}}}, {{{{2, 0}}}}}};
 
-
     std::vector<Point<spacedim>> vertices;
     std::vector<CellData<dim>>   cells;
     SubCellData                  subcell_data;
@@ -8449,12 +8445,18 @@ namespace GridGenerator
     // (ii) create new barycenter vertex location
     for (const auto &cell : ref_tria.cell_iterators())
       {
+        AssertThrow(
+          cell->reference_cell().is_simplex(),
+          ExcMessage(
+            "Cell with invalid ReferenceCell encountered. GridGenerator::alfeld_split_of_simplex_mesh() "
+            "only supports simplex meshes as input."));
+
         // temporary array storing the global indices of each cell entity in the
         // sequence: vertices, edges/faces, cell
-        std::array<unsigned int, dim == 2 ? 4 : 5> local_vertex_indices;
+        std::array<unsigned int, 4> local_vertex_indices;
 
         // (i) copy the existing vertex locations
-        Tensor<1, spacedim> barycenter;
+        Point<spacedim> barycenter;
         for (const auto v : cell->vertex_indices())
           {
             const auto v_global = cell->vertex_index(v);
@@ -8474,7 +8476,7 @@ namespace GridGenerator
 
         // (ii) barycenter:
         local_vertex_indices[3] = vertices.size();
-        vertices.push_back(Point<spacedim>() + barycenter / 3.);
+        vertices.push_back(barycenter / 3.);
 
         // helper function for creating cells and subcells
         const auto add_cell = [&](const unsigned int struct_dim,
@@ -8490,14 +8492,7 @@ namespace GridGenerator
 
           if (struct_dim == dim) // cells
             {
-              if (dim == 2)
-                {
-                  AssertDimension(index_vertices.size(), 3);
-                }
-              else if (dim == 3)
-                {
-                  AssertDimension(index_vertices.size(), 4);
-                }
+              AssertDimension(index_vertices.size(), dim + 1);
 
               CellData<dim> cell_data(index_vertices.size());
               for (unsigned int i = 0; i < index_vertices.size(); ++i)
@@ -8506,11 +8501,10 @@ namespace GridGenerator
                                    local_vertex_indices.size());
                   cell_data.vertices[i] =
                     local_vertex_indices[index_vertices[i]];
-                  cell_data.material_id =
-                    material_or_boundary_id; // inherit material id
-                  cell_data.manifold_id =
-                    manifold_id; // inherit cell-manifold id
                 }
+              cell_data.material_id =
+                material_or_boundary_id;           // inherit material id
+              cell_data.manifold_id = manifold_id; // inherit cell-manifold id
               cells.push_back(cell_data);
             }
           else if (dim == 2 && struct_dim == 1) // an edge of a simplex