Clustering analysis of periodic point vortices with the L function

The motion of point vortices with periodic boundary conditions was studied by using Weierstrass zeta functions. The scattering and recoupling of a vortex pair by a third vortex becomes remarkable when the vortex density is large. The clustering of vortices with various initial conditions is quantitated by the L function used in the point process theory in spatial ecology. It is shown that clustering persists if the initial distribution is clustered like an infinite row or a checkered pattern.