THE OPTIMAL N-BODY METHOD FOR STABILITY STUDIES OF GALAXIES

The stability of a galaxy model is most easily assessed through N-body simulation. Particle-mesh codes have been widely used for this purpos e, since they enable the largest number of particles to be employed. W e show that the functional expansion technique, originally proposed by Clutton-Brock for other simulation problems, is in fact superior for stability work. For simulations of linear evolution, it is not much sl ower than grid methods using the same number of particles and reproduc es analytical results with much greater accuracy. This success rests o n its ability to represent global modes with a modest number of basis functions; grid methods may be more effective for other applications h owever. Our conclusions are based on implementations of functional exp ansion and grid algorithms for disk galaxies.