Gravitational Encounters and the Evolution of Galactic Nuclei. I. Method
  An algorithm is described for evolving the phase-space density of stars or
compact objects around a massive black hole at the center of a galaxy. The
technique is based on numerical integration of the Fokker-Planck equation in
energy-angular momentum space, f(E,L,t), and includes, for the first time,
diffusion coefficients that describe the effects of both random and correlated
encounters (resonant relaxation), as well as energy loss due to emission of
gravitational waves. Destruction or loss of stars into the black hole are
treated by means of a detailed boundary-layer analysis. Performance of the
algorithm is illustrated by calculating two-dimensional, time-dependent and
steady-state distribution functions and their corresponding loss rates.
