Dear all, I calculated the eigenvectors of a unitary matrix with Maple10. (that is, I'm dealing complex vector space) Also, I computed it with C program made by myself. The eigenvalues coincide in two methods up to their order. But eigenvectors are different up to complex phase. Let me say, Let E_M(i) be the i-th eigenvector of the given matrix A calculated by Maple10 and let E_C(j) be the j-th eigenvector of A computed by the C program. Both of them are eigenvectors of A, that is, A&*E_M(i) = lambda(i)*E_M(i) and A&*E_C(i) = lambda(i)*E_C(i) are satisfied. But, dotprod(E_C(i), E_M(j)) != kronecker_delta(i,j).