CHAPTER 1 1-1 NUMERICAL METHODS For the last two or three decades, scientists and engineers have used numerical methods as an important tool in many different areas. This significant fact has its inexorable historical trend and it is the inevitable outcome of the recent developments in science, technology and industry. Analytical methods have been developed for a long period and have produced a great amount of successful results, but they failed to solve most practical engineering problems with complicated boundary conditions or irregular geometry. It is also very difficult to solve non-linear or time-dependent problems using analytical approaches, even if they are very simple. On the other hand, research on analytical methods has provided a solid foundation for different types of numerical methods. Because of the rapid developments of science and technology it is now necessary to solve complicated problems using more efficient and accurate approaches than before. Not only problems with complicated boundary conditions or irregular configurations require solutions but also non-linear or time-dependent problems must be solved. Computer hardware and software have developed at an unexpected high speed. During the last thirty years, ithaz become possible for scientists and engineers to use numerical methods with computers easily. This has 2 stimulated scientists and engineers to improve some classical numerical methods (such as finite difference method) and to establish new numerical methods (such as the finite element method and boundary element method). For all these reasons, numerical methods have rapidly developed in the areas of mechanics and engineering.