Hi Emmanuel,
Eigenvectors are not defined uniquely, in the sense that if v is an eigenvector of M, then any nonzero constant times v is also an eigenvector of M. In your case for eigenvalue 0, the book eigenvector is [2; -1] and the Matlab eigenvector is V(:,1) = [-.8944; .4472]. These differ only by an overall multiplicative constant. Similarly for eigenvalue 5, [1; 2] and [.4472; .8944] differ only by an overall multiplicative constant. It's necessary to make a definite choice and Matlab defines its eigenvectors so that norm(eigenvector) = 1 but this is not a requirement.
