sentences:  The model is a Hamiltonian system of "N" points in the two-dimensional plane executing the motion
  
  In the point-vortex gas interpretation, the particles represent either point vortices in a two-dimensional fluid, or parallel line vortices in a three-dimensional fluid.The constant "k""i" is the circulation of the fluid around the "i"th vortex.The Hamiltonian "H" is the interaction term of the fluid's integrated kinetic energy; it may be either positive or negative.