Upper and Lower Solutions to a Coupled System of Nonlinear Fractional Differential Equations

In this article, we investigate upper and lower solutions to a system of coupled nonlinear fractional differential equa tions with multi-point coupled boundary conditions. Using monotone type iterative techniques combined with the upper and lower solutions method, some necessary and sufficient conditions are develo ped to guarantee existence of multiple solutions of the problem. The main result is demonstrated by analyzing two test problems.