Optimal existence conditions for second order periodic solutions of delay differential equations with upper and lower solutions in the reverse order

Abstract

In this paper we show that the monotone iterative technique provides two monotone sequences that converge uniformly to extremal (periodic) solutions of second order delay differential equations without assuming properties of monotonicity in the nonlinear part. Moreover, we obtain optimal existence conditions with upper and lower solutions in the reverse order. Our results are new even for ordinary differential equations.

Keywords:

• Periodic solution
• Existence
• Upper and lower solution
• Monotone iterative technique

Acknowledgement

The work was supported by NNSF of China.