If the physical problem has several variables per grid point, that is, if there are several coupled partial differential equations, it is possible to introduce blocking in a natural way.
Blocking of the equations (which gives a small number of very large blocks) was used by Axelsson and Gustafsson [17] for the equations of linear elasticity, and blocking of the variables per node (which gives many very small blocks) was used by Aarden and Karlsson [1] for the semiconductor equations. A systematic comparison of the two approaches was made by Bank, et al. [26].