Differential and difference maximum principles

The maximum principle enables us to obtain information about solutions of differential equations without any explicit knowledge of the solutions themselves. In particular the maximum principle is a useful tool in the approximation of solutions.In this study, the maximum principle for second order first type self-adjoint boundary value problems is investigated as an entrance. Then the principle is discussed for non self-adjoint problems. The maximum principle and its applications are expressed and proved for third type boundary value problems after it is discussed for a second order non self-adjoint periodical problem. Finally, the principle and its applications are studied for difference boundary value problems.