ABSTRACT
In this chapter we discuss some elementary perturbation methods for solving initial and boundary value problems. Only regular perturbation methods are presented. We leave singular perturbation techniques for more advanced textbooks. The solution of a perturbed problem in a regular perturbation approaches the solution of the unperturbed problem as the perturbation parameter approaches a specific limit. A perturbed problem may arise either due to a small variation in the governing differential equation or due to a slight perturbation of the boundary of the domain under consideration.
