Two-dimensional illustration of the mesh indexing in RASCAS. A level l oct has five pointers (seven in 3D) to level l − 1 cells: the cell containing the oct (father, red arrow) and the four neighbours (six in 3D) (green arrows). A cell at level l − 1 has a pointer son either to an oct at level l if it is refined (blue arrow, left) or to the physical properties describing of the cell if it is a leaf cell (i.e. it is not refined; blue arrow, right). See text for a comprehensive description.