B=[9 -4 -2 -4
    -56 32 -28 44
    -14 -14 6 -14
    42 -33 21 -45]
ev=eig(B)
null(B-ev(1)*eye(4))
null(B-ev(2)*eye(4))
[V,d]=eig(B)	    

A=[0 13 8 4
    4 9 8 4
    8 6 12 8
    0 5 0 -4
    ]
ev=eig(A)
null(A-ev(1)*eye(4))
null(A-ev(2)*eye(4))
null(A-ev(3)*eye(4))
[V,d]=eig(A)	    
(A-ev(3)*eye(4))*null(A-ev(3)*eye(4))
(A-ev(3)*eye(4))*V
