A = matrix([[6, -2, 3, 0],[1, 3, 0, 1],[1, -2, 6, -2],[2, 1, 3, 7]])
D = matrix([[6, 0,0, 0],[0, 3, 0, 0],[0, 0, 6, 0],[0, 0, 0, 7]])
L = matrix([[0,0,0, 0],[-1, 0,0,0],[-1, 2, 0,0],[-2, -1, -3, 0]])
U = matrix([[0, 2, -3, 0],[0,0, 0, -1],[0,0,0, 2],[0,0,0,0]])
tmp = (D - L).inverse()
T = tmp*U
show(A.eigenvalues())