1 -3 4 0
-1 4 -5 a
1 -1 3 5
-1 2 b-2 -1
r2+r1,r3-r1,r4+r1
1 -3 4 0
0 -1 -1 a
0 2 -1 5
0 -1 b+2 -1
r3+2r2,r4-r2
1 -3 4 0
0 -1 -1 a
0 0 -3 2a+5
0 0 b+3 -1-a
暂时只能化到这里了