# File lib/graphviz/math/matrix.rb, line 180
      def remove_column(n)
        unless (0...@column).to_a.include?(n-1)
          raise CoordinateError, "Column out of range (#{n} for 1..#{@column})!"
        end

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