例2设初等矩阵 0010 1 0100 k P P 1000 1 0001 C 求PP2P3及(PP2P3 01 0 1 1P2B3 0 0 C C              =               =               = 1 1 1 1 1 1 1 0 0 0 1 1 0 0 0 0 1 0 0 0 0 1 0 2 1 2 3 k P c P P 例 设初等矩阵 1 1 2 3 1 2 3 ( ) − 求P P P 及 P P P               = 1 1 0 0 1 c k                              = 1 1 1 1 1 0 1 0 1 1 2 3 k c PP P