How to merge two triangulation?

[Deepika Kushwah]

Hello Everyone, 

I am trying to merge two triangulations and the code is here: 

int main ()
{
  Triangulation<2> final_triangulation;

  Triangulation<2> first_triangulation;
  const std::vector<Point<2>> vertices = {
                        Point<2>(0.0, 0.0),
                        Point<2>(1.0, 0.0),
                        Point<2>(0.0, 1.0),
                        Point<2>(1.0, 1.0)};

   const std::vector<std::array<int,GeometryInfo<2>::vertices_per_cell>>
    cell_vertices = {{{0, 1, 2, 3}}};
   
    const unsigned int n_cells = cell_vertices.size();
   
   std::cout<<"cells"<<" "<<n_cells<<std::endl;
   
   std::vector<CellData<2>> cells_1(n_cells, CellData<2>());
   
  for (unsigned int i = 0; i < n_cells; ++i)
  {
    for (unsigned int j = 0; j < cell_vertices[i].size(); ++j)
    {
      cells_1[i].vertices[j] = cell_vertices[i][j];
      cells_1[j].material_id = 3;
    }
     cells_1[i].material_id = 4;
     
  }
 first_triangulation.create_triangulation (vertices, cells_1, SubCellData());
 
 
  Triangulation<2> second_triangulation;
  const std::vector<Point<2>> vertices_1 = {
                        Point<2>(0.0, 1.0),
                        Point<2>(1.0, 1.0),
                        Point<2>(0.0, 2.0),
                        Point<2>(1.0, 2.0)};

   const std::vector<std::array<int,GeometryInfo<2>::vertices_per_cell>>
    cell_vertices_1 = {{{2, 3, 4, 5}}};
   
    const unsigned int n_cells_1 = cell_vertices_1.size();
   
   std::cout<<"cells_2"<<" "<<n_cells<<std::endl;
   
   std::vector<CellData<2>> cells_2(n_cells_1, CellData<2>());
   
  for (unsigned int i = 0; i < n_cells_1; ++i)
  {
    for (unsigned int j = 0; j < cell_vertices_1[i].size(); ++j)
    {
      cells_2[i].vertices[j] = cell_vertices_1[i][j];
      cells_2[j].material_id = 1;
    }
     cells_2[i].material_id = 2;
     
  }
 
   second_triangulation.create_triangulation (vertices_1, cells_2, SubCellData());
 
   GridGenerator::merge_triangulations(first_triangulation,
                            second_triangulation,
                            final_triangulation);
                           

  //final_triangulation.refine_global(0);
  //final_triangulation.set_all_manifold_ids_on_boundary(42);
 
  //final_triangulation.execute_coarsening_and_refinement();
  std::ofstream out("grid-1.vtk");
  GridOut       grid_out;
  grid_out.write_vtk(final_triangulation, out);
  std::cout << "Grid written to grid-1.vtk" << std::endl;
   }

But this is showing the following error:

[ 66%] Linking CXX executable try2
[ 66%] Built target try2
[100%] Run try2 with Debug configuration
cells 1
cells_2 1

--------------------------------------------------------
An error occurred in line <602> of file <./source/grid/grid_tools.cc> in function
    std::tuple<std::vector<dealii::Point<spacedim, double>, std::allocator<dealii::Point<spacedim, double> > >, std::vector<dealii::CellData<dim>, std::allocator<dealii::CellData<dim> > >, dealii::SubCellData> dealii::GridTools::get_coarse_mesh_description(const dealii::Triangulation<dim, spacedim>&) [with int dim = 2; int spacedim = 2]
The violated condition was:
    std::find(used_vertices.begin(), used_vertices.end(), false) == used_vertices.end()
Additional information:
    The level zero vertices should form a contiguous range.

Stacktrace:
-----------
#0  /lib/x86_64-linux-gnu/libdeal.ii.g.so.9.3.2: std::tuple<std::vector<dealii::Point<2, double>, std::allocator<dealii::Point<2, double> > >, std::vector<dealii::CellData<2>, std::allocator<dealii::CellData<2> > >, dealii::SubCellData> dealii::GridTools::get_coarse_mesh_description<2, 2>(dealii::Triangulation<2, 2> const&)
#1  /lib/x86_64-linux-gnu/libdeal.ii.g.so.9.3.2: void dealii::GridGenerator::merge_triangulations<2, 2>(std::vector<dealii::Triangulation<2, 2> const*, std::allocator<dealii::Triangulation<2, 2> const*> > const&, dealii::Triangulation<2, 2>&, double, bool)
#2  /lib/x86_64-linux-gnu/libdeal.ii.g.so.9.3.2: void dealii::GridGenerator::merge_triangulations<2, 2>(dealii::Triangulation<2, 2> const&, dealii::Triangulation<2, 2> const&, dealii::Triangulation<2, 2>&, double, bool)
#3  ./try2: main
--------------------------------------------------------

make[3]: *** [CMakeFiles/run.dir/build.make:71: CMakeFiles/run] Aborted (core dumped)
make[2]: *** [CMakeFiles/Makefile2:116: CMakeFiles/run.dir/all] Error 2
make[1]: *** [CMakeFiles/Makefile2:123: CMakeFiles/run.dir/rule] Error 2
make: *** [Makefile:137: run] Error 2

I am not able to understand this error message.

 How to resolve this error? Please help.

Thanks & Regards,

Deepika

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