# File lib/ai4r/clusterers/single_linkage.rb, line 110
      def update_distance_matrix(ci, cj)
        ci, cj = cj, ci if cj > ci
        distances_to_new_cluster = Array.new
        (@distance_matrix.length+1).times do |cx|
          if cx!= ci && cx!=cj
            distances_to_new_cluster << linkage_distance(cx, ci, cj) 
          end
        end
        if cj==0 && ci==1
          @distance_matrix.delete_at(1) 
          @distance_matrix.delete_at(0)         
        elsif cj==0
          @distance_matrix.delete_at(ci-1) 
          @distance_matrix.delete_at(0) 
        else
          @distance_matrix.delete_at(ci-1) 
          @distance_matrix.delete_at(cj-1)
        end
        @distance_matrix.each do |d| 
          d.delete_at(ci)
          d.delete_at(cj)
        end
        @distance_matrix << distances_to_new_cluster
      end