ABSTRACT
A large fraction of classical, and also quantum, physics uses a common type of mathematics. Certain partial differential equations occur over and over again in different fields. The methods of solution of these equations and the special functions which arise are thus generally useful tools which should be known to all physicists. Similar courses are offered in mathematics departments. There, one is usually concerned with the rigorous logical development of the mathematics. The student interested in such matters should and must go to the mathematicians. A similar equation is obtained for processes involving the diffusion of particles. The pressure and density fluctuations thus satisfy the three dimensional wave equation with the velocity of the waves. The nonlinear terms lead to various interesting phenomena such as shock waves.
