def print
      warn "Cluster: mean = #{mean}, density = #{density}"
      lengths.sort { |a, b| a <=> b }.each do |elem|
        warn "#{elem[0]}, #{elem[1]}"
      end
      warn '--------------------------'
    end
def print
      warn "Cluster: mean = #{mean}, density = #{density}"
      lengths.sort { |a, b| a <=> b }.each do |elem|
        warn "#{elem[0]}, #{elem[1]}"
      end
      warn '--------------------------'
    end
Prints the current cluster