4×4矩阵B=
1 0 0 1
1 2 3 -1
3 -1 0 4
1 4 5 2 r1-r1,r3-3r1,r4-r1
~
1 0 0 1
0 2 3 -2
0 -1 0 1
0 4 5 1 r4-2r2,r2+2r3
~
1 0 0 1
0 0 3 0
0 -1 0 1
0 0 -1 5 r2/3,r4+r2,r3*(-1),交换行次序
~
1 0 0 1
0 1 0 -1
0 0 1 0
0 0 0 5 r4/5,r1-r4,r2+r4
~
1 0 0 0
0 1 0 0
0 0 1 0
0 0 0 1
所以矩阵的秩为r(B)=4