9类平均法( Average linkage) ∑∑叭(X,X) p'q XEGp Xi p>q ∑∑d(X1,X pg Xi∈CpX/∈Gq类平均法(Average linkage)     = Xi Gp X j Gq i j p q p q d X X n n d G G ( , ) 1 ( , )     = Xi Gp X j Gq i j p q p q d X X n n d G G ( , ) 1 ( , ) 2 2