# File lib/extras/as_rectarray.rb, line 32
        def invertCols!
                (@cols/2).times do|j|
                        for i in 0...@rows do
                                a = index(i,j)
                                b = index(i,@cols - 1 - j)
                                temp = @arr[a]
                                @arr[a] = @arr[b]
                                @arr[b] = temp
                        end
                end
        end