11 Concluding comments It
Perhaps more importantly, a variety of styles are represented on how to treat and interpret the potential function, and how to treat the variables. These may roughly be sUl11T1arised as follows: (1) seek the equilibrium manifold directly - as with Amson, Papageorgiou and, to some extent, Poston and Wilson and then interpret the results in terms of catastrophe theory; (2) define variables carefully, and then use the canonical form of surface - Casti and Swain, Mees, Isard, Wagstaff and Dendrinos. In this second category, we have seen many ways of handling the variables within this framework. The obvious thing to do is to take the state variables as the main dependent variables of the system of interest (Casti and Swain, t1ees, Isard and Dendrinos), but Wagstaff has also shown that the main variable can be taken as the potential function. It is also possible in some cases to take space and/ or time as control variables.