how to refine only the outer cells of a mesh?

[Loylick]

Hello!

I have hyper_ball triangulation refined couple of times globally. Now I want to refine only the cells which lay on the surface. In tutorial I've found the function refine_and_coarsen_fixed_number but I have not arrived at formulating the proper criteria. In examples you use a solution to buld the critaria to refine adaptively a mesh. What is the most simple way to make it?

Alex

[Daniel Arndt]

Alex,

have a look at step-1. The relevant piece of code there looks like

Triangulation<2>::active_cell_iterator cell = triangulation.begin_active();

Triangulation<2>::active_cell_iterator endc = triangulation.end();

for (; cell!=endc; ++cell)

{

  for (unsigned int v=0; v < GeometryInfo<2>::vertices_per_cell; ++v)

  {

    const double distance_from_center = center.distance (cell->vertex(v));

    if (std::fabs(distance_from_center - inner_radius) < 1e-10)

    {

      cell->set_refine_flag ();

      break;

    }

  }

}

triangulation.execute_coarsening_and_refinement ();

For your purpose, it should be sufficient to check for cell->at_boundary().

Best,

Daniel