Polynomial Solutions of Linear Differential Equations: Spectral Problems, Asymptotic and WKB-Analysis

Linear ordinary differential equations with polynomial coefficients and their solutions in the complex plane have been an active area of mathematical research since the mid-19th century, with contributions from such prominent figures as G. Lamé, M. Bôcher, E. Heine, F. Klein, T. Stieltjes, G. D. Birkhoff, and many others. During the 19th century, interest focused mainly on second-order equations because of their importance in physics. The existence of a polynomial solution to a linear diffe...