Cluster networks and Bruhat-Tits buildings
  Clustering procedure for the case where instead of a fixed metric one applies a family of metrics is considered. In this case instead of a classification tree one obtains a classification network (a directed acyclic graph with non directed cycles).   Relation to Bruhat-Tits buildings is discussed. Dimension of a general cluster system is considered. 
S.V. Kozyrev
math.MG cs.DM