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].

Mon Nov 20 08:52:54 EST 1995