Gomilko, A. M., & Pivovarchik, V. N. (2001). Asymptotics of Solutions of the Sturm–Liouville Equation with Respect to a Parameter.
Ukrains’kyi Matematychnyi Zhurnal
,
53
(6), 742-757.
https://umj.imath.kiev.ua/index.php/umj/article/view/4297