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Published online by Cambridge University Press: 04 August 2017
Since galaxies are collisionless relaxed systems, actions are an extremely useful tool for understanding their dynamics. There are many potential applications of actions: (1) When orbits in an N-body simulation are characterized by their actions, the six dimensional distribution function, can be reduced to a more tractable three dimensional function, f(J). (2) Actions are adiabatic invariants, and thus are useful for studying slowly evolving systems. Binney, May and Ostriker (1986) have applied this technique to study the response of the spheroid to the disc. (3) the spectral decomposition of an orbit can be used to help generate self–consistent galaxy models (Spergel 1987).