Change Change VTK output for general polyhedral meshes

Now the polyhedral connectivity is only stored when needed (that is
when general polyhedrons are present). This improves a lot the
creation of output files.

src/output/VTKWriter.hpp

@@ -322,6 +322,8 @@ class VTKWriter
       {
         Array<int8_t> types(mesh->numberOfCells());
         const auto& cell_type           = mesh->connectivity().cellType();
+        const auto& cell_to_node_matrix = mesh->connectivity().cellToNodeMatrix();
+
         parallel_for(
           mesh->numberOfCells(), PUGS_LAMBDA(CellId j) {
             switch (cell_type[j]) {
@@ -342,7 +344,11 @@ class VTKWriter
               break;
             }
             case CellType::Pyramid: {
-              types[j] = 14;
+              if (cell_to_node_matrix[j].size() == 5) {
+                types[j] = 14;   // quadrangle basis
+              } else {
+                types[j] = 41;   // polygonal basis
+              }
               break;
             }
             case CellType::Prism: {
@@ -365,10 +371,16 @@ class VTKWriter
             }
           });
         _write_array(fout, "types", types);
-      }
         if constexpr (MeshType::Dimension == 3) {
+          const bool has_general_polyhedron = [&] {
+            for (size_t i = 0; i < types.size(); ++i) {
+              if (types[i] == 41)
+                return true;
+            }
+            return false;
+          }();
+          if (has_general_polyhedron) {
             const auto& cell_to_face_matrix   = mesh->connectivity().cellToFaceMatrix();
-        const auto& cell_to_node_matrix   = mesh->connectivity().cellToNodeMatrix();
             const auto& face_to_node_matrix   = mesh->connectivity().faceToNodeMatrix();
             const auto& cell_face_is_reversed = mesh->connectivity().cellFaceIsReversed();
 
@@ -422,6 +434,9 @@ class VTKWriter
             }
             fout << "</DataArray>\n";
           }
+        }
+      }
+
       fout << "</Cells>\n";
       fout << "</Piece>\n";
       fout << "</UnstructuredGrid>\n";