    # File lib/graphviz/math/matrix.rb, line 163
          def remove_line(n)
            unless (0...@line).to_a.include?(n-1)
              raise CoordinateError, "Line out of range (#{n} for 1..#{@line})!"
            end

            matrix = GraphViz::Math::Matrix.new( @line - 1, @column )
            nline = 0
            @line.times do |line|
              next if line == n - 1
              @column.times do |column|
                matrix[nline+1, column+1] = self[line+1, column+1]
              end
              nline += 1
            end
            return matrix
          end