1-λ a a a
a 1-λ a a
a a 1-λ a
a a a 1-λ
c1+c2+c3+c4
3a+1-λ a a a
3a+1-λ 1-λ a a
3a+1-λ a 1-λ a
3a+1-λ a a 1-λ
=
ri-r1，i=2，3，4
0 1-a-λ 0 0
0 0 1-a-λ 0
0 0 0 1-a-λ
= (3a+1-λ)(1-a-λ)^3.
所以R的特征值為λ 1 = 3a+1，λ 2 = λ 3 = λ 4 = 1-a。