Eigenfunction Expansions Associated with Second-order Differential Equations

Book excerpt: Vol. 1. The Sturm-Liouville expansion -- The singular case : series expansions -- The general singular case -- Examples -- The nature of the spectrum -- An alternative method : transform theory -- The distribution of the eigenvalues -- General theorems on eigenfunctions -- Convergence of the expansion under Fourier conditions -- Summability -- vol. 2. Expansions in a rectangle -- Expansions in the whole plane -- Extensions of the theory -- Variation of the eigenvalues : the problem of the general finite region -- Separable equations -- The nature of the spectrum -- The distribution of the eigenvalues -- Convergence and summability theorems -- Perturbation theory -- Perturbation theory involving continuous spectra -- The case in which q(x) is periodic -- Miscellaneous theorems.