Orthogonal Functions - Sansone, Giovanni, and Diamond, Ainsley H (Translated by), and Hille, Einar (Foreword by)

Easy to read but rigorous in its attention to detail and technique, this graduate-level text covers expansion in a series of orthogonal functions and preliminary notions of Hilbert space, expansion in Fourier series and in series of Legendre polynomials and spherical harmonics, and expansions in Laguerre and Hermite series.

Orthogonal Functions 2004, Dover Publications, Mineola, NY

ISBN-13: 9780486438016