阿理第2步等价于:若a2≠0时,用矩阵 010 2)(i=34,…,n) a 12 22a2 左乘2,即有:2421=00a43…a9=A0 nn(3) (3) (3) 3 (3) 3 (3) 3 3 (2) 2 (2) 2 3 (2) 2 2 (1) 1 (1) 1 3 (1) 1 2 (1) 1 1 2 2 2 (2) 2 2 (2) 2 2 2 2 3 2 (2) 2 2 0 0 ... ... ... ... ... ... 0 0 ... 0 ... ... : ( 3,4,..., ) 0 0 ... 1 ... ... ... 0 1 ... 0 0 1 0 ... 0 1 0 0 ... 0 2 0 A a a a a a a a a a a a A L A i n a a l l L l a n n n n n n ( ) ( ) i i n =                 = = =                 − = −  左乘 ，即有 同理第 步等价于：若 时，用矩阵  