Optimal implementations of UPGMA and other common clustering algorithms.

Ilan Gronau Shlomo Moran Optimal implementations of UPGMA and other common clustering algorithms. 205-210 2007 104 Inf. Process. Lett. 6 http://dx.doi.org/10.1016/j.ipl.2007.07.002 db/journals/ipl/ipl104.html#GronauM07