Variational principles for real eigenvalues of self-adjoint operator pencils in non-separated root zones are studied.
HASANOV, MAHİR (2007) "Spectral Problems for Operator Pencils in Non-Separated Root Zones," Turkish Journal of Mathematics: Vol. 31: No. 1, Article 3. Available at: https://journals.tubitak.gov.tr/math/vol31/iss1/3