 The figure below show the effect of two refinement iterations on a T-shaped quadrilateral mesh.Just as for Catmull–Clark surfaces, Doo–Sabin limit surfaces can also be evaluated directly without any recursive refinement, by means of the technique of Jos Stam.The solution is, however, not as computationally efficient as for Catmull-Clark surfaces because the Doo–Sabin subdivision matrices are not in general diagonalizable.