Marletta, Marco Everitt, W. N. Zettl, A. Inequalities and eigenvalues of Sturm-Liouville problems near a singular boundary We study the behavior of eigenvalues of Sturm-Liouville problems (SLP) when an endpoint of the underlying interval approaches a singularity. Sturm-Liouville;Eigenvalues;Singular endpoint 2015-06-30
    https://figshare.le.ac.uk/articles/journal_contribution/Inequalities_and_eigenvalues_of_Sturm-Liouville_problems_near_a_singular_boundary/10164302