  We define the local periodic linking number, LK, between two oriented closed
or open chains in a system with three-dimensional periodic boundary conditions.
The properties of LK indicate that it is an appropriate measure of entanglement
between a collection of chains in a periodic system. Using this measure of
linking to assess the extent of entanglement in a polymer melt we study the
effect of CReTA algorithm on the entanglement of polyethylene chains. Our
numerical results show that the statistics of the local periodic linking number
observed for polymer melts before and after the application of CReTA are the
same.
