B.M. Brown, M. Langer, M. Marletta, C. Tretter and M. Wagenhofer,
Eigenvalue bounds for the singular Sturm–Liouville problem
with a complex potential,
J. Phys. A 36 (2003), 3773–3787
Abstract:
The main objective of this paper is to report on a recent algorithm to
enclose the eigenvalues of non-selfadjoint singular Sturm–Liouville problems.