ABSTRACT
The prototype model takes into account the "major features" of the system at hand and ignores other aspects which might have "small impact" on the system evolution. In other words the prototype model reduces the system to its "bare bones". In many cases these prototype models lead to equations with closed form solutions, viz. solutions in terms of analytical formulas. The essence of perturbation theory and techniques is to develop methods that yield at least approximate solutions for these refined models. This chapter presents some of the basic techniques of perturbations theory. It illustrates how the regular perturbation procedure is used to obtain an approximate solution of an equation with a term which is "small" compared to other terms. In general, when the perturbation term is small, its impact on the solution of the corresponding equation without the perturbation term will be small.
