# File lib/matrix.rb, line 305
  def column(j) # :yield: e
    if block_given?
      0.upto(row_size - 1) do
        |i|
        yield @rows[i][j]
      end
    else
      col = (0 .. row_size - 1).collect {
        |i|
        @rows[i][j]
      }
      Vector.elements(col, false)
    end
  end