# File lib/backports/1.9.2/stdlib/matrix.rb, line 357
  def column(j) # :yield: e
    if block_given?
      return self if j >= column_size || j < -column_size
      row_size.times do |i|
        yield @rows[i][j]
      end
      self
    else
      return nil if j >= column_size || j < -column_size
      col = Array.new(row_size) {|i|
        @rows[i][j]
      }
      Vector.elements(col, false)
    end
  end