Controling the refinement of an element

In legacy (old) dolfin, there’s a parameter:

parameters["refinement_algorithm"]

which has the options

[plaza,plaza_with_parent_facets,regular_cut]

You can read the source to find out exactly what these do. But I believe the most popular is plaza refinement with parent facets since it preserves parent-child information between refinement levels.

Two reasons for bisecting into 4 rather than 2 simplices:

  1. Old dolfin doesn’t support non-conforming meshes, you cannot have hanging nodes.
  2. Following the previous point, it’s important to preserve mesh quality. This is extremely difficult if you restrict yourself to bisection of triangles only.