    # 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