THE UPPER AND LOWER BOUNDS ON NON-REAL EIGENVALUES OF INDEFINITE STURM-LIOUVILLE PROBLEMS.

The present paper gives a priori upper and lower bounds on nonreal eigenvalues of regular indefinite Sturm-Liouville problems only under the integrability conditions. More generally, a lower bound on non-real eigenvalues of the self-adjoint operator in Krein space is obtained. [ABSTRACT FROM AUTHOR]