M. V. BerryH H Wills Physics Laboratory,
Bristol, United Kingdom.
C. J. HowlsSchool of Mathematics,
University of Southampton,
Southampton, United Kingdom.
There is no single source covering the material in this chapter. An overview
of some of the mathematical analysis is given in Arnol’d (1975, 1986). Many physical applications can be found in
Poston and Stewart (1978). For applications to wave physics, especially optics,
see Berry and Upstill (1980).