# File lib/backports/1.9.2/stdlib/matrix/lup_decomposition.rb, line 47
    def p
      rows = Array.new(@row_size){Array.new(@col_size, 0)}
      @pivots.each_with_index{|p, i| rows[i][p] = 1}
      Matrix.send :new, rows, @col_size
    end