1. Armentano M, Duŕan R. Asymptotic lower bounds for eigenvalues by nonconforming finite element methods. ETNA, 2004, 17: 93–101
2. Babuška I, Osborn J. Finite element Galerkin approximation of the eigenvalues and eigenvectors of selfadjoint problem. Math Comput, 1989, 52: 275–297
3. Babuška I, Osborn J. In: Ciarlet P G, Lions J L, eds. Eigenvalue Problems. Handbook of Numerical Analysis, V. II: Finite Element Methods (Part I). North-Holland: Elsevier, 1991
4. Ciarlet P. The Finite Element Method for Elliptic Problems. Amsterdam: North-Holland, 1978
5. Chatelin F. Spectral Approzimations of Linear Operators. New York: Academic Press, 1983