Orthogonal Functions - Dover Phoenix Editions Author:G. Sansone The theory of orthogonal expansions originated 200 years ago, with a debate over the motion of a vibrating string that animated the mathematical world. The theory has since developed into an important area of modern mathematical thought, and this highly regarded treatise presents the classical theory of orthogonal series. Easy to read but rigoro... more »us in its attention to detail and appropriate technique, this graduate-level text contains a wealth of factual and bibliographical information. A rich compilation of general results and convenient criteria, this volume opens with a chapter on expansion in a series of orthogonal functions and preliminary notions of Hilbert space. It advances to expansion in Fourier series and in series of Legendre polynomials and spherical harmonics, concluding with expansions in Laguerre and Hermite series. 1959 ed.« less