四阶行列式的计算 abcd badc dcba cdab

a b c d
b a d c
c d a b
d c b a
c1+c2+c3+c4
a+b+c+d b c d
a+b+c+d a d c
a+b+c+d d a b
a+b+c+d c b a
r2-r1,r3-r1,r4-r1
a+b+c+d b c d
0 a-b d-c c-d
0 d-b a-c b-d
0 c-b b-c a-d
c2+c3
a+b+c+d b+c c d
0 a-b-c+d d-c c-d
0 a-b-c+d a-c b-d
0 0 b-c a-d
r3-r2
a+b+c+d b+c c d
0 a-b-c+d d-c c-d
0 0 a-d b-c
0 0 b-c a-d
c3+c4
a+b+c+d b+c c d
0 a-b-c+d d-c c-d
0 0 a+b-c-d b-c
0 0 a+b-c-d a-d
r4-r3
a+b+c+d b+c c d
0 a-b-c+d d-c c-d
0 0 a+b-c-d b-c
0 0 0 a-b+c-d
行列式 = (a+b+c+d)(a-b-c+d)(a+b-c-d)(a-b+c-d).

2*a^2*b^2-a^4-8*a*c*d*b+2*c^2*a^2+2*d^2*a^2-b^4+2*c^2*b^2+2*d^2*b^2+2*d^2*c^2-d^4-c^4


syms a b c d;x=[a b c d;b a d c;d c b a;c d a b]

x =

[ a, b, c, d]
[ b, ...