We introduce the concept of single-linkage equivalence of edge-weighted graphs, we apply it to characterise maximal spanning trees and "ultrasimilarities", and we discuss how it relates to the popular single-linkage clustering algorithm. Key words and phrases: Edge-weighted graphs, single-linkage clustering, maximal/minimal spanning trees, single-linkage equivalence, edge equivalence, ultra-similarities, ultra-metrics, subdominant ultra-metrics.
Andreas W. M. Dress, Taoyang Wu, XiaoMing Xu