Extremal system of solutions for a coupled system of nonlinear fractional differential equations by monotone iterative method

In this paper, we deal with a coupled system of nonlinear fractional differential equations, which involve the Riemann-Liouville derivatives of different fractional orders. By using the monotone iterative technique combined with the method of upper and lower solutions, we not only obtain the existence of extremal system of solutions, but also establish iterative sequences for approximating the solutions. As an application, an example is given to illustrate our main results.