A semi-numerical method for periodic orbits in a bisymmetrical potential
  We use a semi-numerical method to find the position and period of periodic orbits in a bisymmetrical potential, made up of a two dimensional harmonic oscillator, with an additional term of a Plummer potential, in a number of resonant cases. The results are compared with the outcomes obtained by the numerical integration of the equations of motion and the agreement is good. This indicates that the semi-numerical method gives general and reliable results. Comparison with other methods of locating periodic orbits is also made. 
Nicolaos D. Caranicolas and Euaggelos E. Zotos
physics.comp-ph