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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  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  for the semiconductor equations. A systematic comparison of the two approaches was made by Bank, et al. .