1. 1Lord Rayleigh, The Theory of Sound, Vol.1, Dover, New York, 1945, pp.109-118, 214-217.
2. 2Courant, R., and Hilbert, D., Methods of Mathematical Physics, Vol.1, Interscience, New York, 1953, pp.343-346.
3. 3Nayfeh, A., Perturbation Methods, Wiley, New York, 1973, pp.68-76.
4. Rates of change of eigenvalues and eigenvectors.
5. Variations of Eigenvalues and Eigenfunctions in Continuum Mechanics