# File lib/ai4r/clusterers/ward_linkage.rb, line 52 def linkage_distance(cx, ci, cj) ni = @index_clusters[ci].length nj = @index_clusters[cj].length nx = @index_clusters[cx].length ( ( ( 1.0* (ni+nx) * read_distance_matrix(cx, ci) ) + ( 1.0* (nj+nx) * read_distance_matrix(cx, cj) ) ) / (ni + nj + nx) - ( 1.0 * nx * read_distance_matrix(ci, cj) / (ni+nj)**2 ) ) end