Fully Dynamic Delaunay Triangulation in Logarithmic Expected Time per Operation Triangulation de Delaunay pleinement dynamique en temps moyen logarithmique par op eration

The Delaunay Tree is a hierarchical data structure that has been introduced in [6] and analyzed in [7,4]. For a given set of sites S in the plane and an order of insertion for these sites, the Delaunay Tree stores all the successive Delaunay triangulations. As proved before, the Delaunay Tree allows the insertion of a site in logarithmic expected time and linear expected space, when the insertion sequence is randomized. In this paper, we describe an algorithm maintaining the Delaunay Tree under insertions and deletions of sites. This can be done in O(log n) expected time for an insertion and O(log logn) expected time for a deletion, where n is the number of sites currently present in the strucuture. For deletions, by expected time, we mean averaging over all already inserted sites for the choice of the deleted sites. The algorithm has been e ectively coded and experimental results are given.