    # File lib/graphviz/math/matrix.rb, line 106
          def *(m)
            matrix = GraphViz::Math::Matrix.new( @line, @line )

            @line.times do |line|
              @line.times do |column|
                l = self.line(line+1)
                c = m.column(column+1)
                v = 0
                l.size.times do |i|
                  v += l[i]*c[i]
                end
                matrix[line+1,column+1] = v
              end
            end

            return matrix
          end