N-body simulations using customised potential-density pair basis sets
  Potential-density pair basis sets can be used for highly efficient N-body simulation codes, but they suffer from a lack of versatility, i.e. a basis set has to be constructed for each different class of stellar system. We present numerical techniques for generating a biorthonormal potential-density pair basis set which has a general specified pair as its lowest order member. We go on to demonstrate how the set can be used to construct N-body equilibria, which we then evolve using an N-body code which calculates forces using the basis set. 
M. J. W. Brown and J. C. B. Papaloizou