Affine-periodic solutions for higher order differential equations

This paper is a continuous work of Liu et al. (2017, first order) and Xu et al. (2019, second order) for affine-periodic solutions to ordinary differential equations. It is a hard problem to obtain satisfied extremum principles. In this paper, we give several extremum principles (Theorem 2.1 and Lemma 2.2) for affine-periodic problems, especially for the case of higher order systems. By these extremum principles, we partly establish the existence of affine-periodic solutions for higher order ordinary differential equations. (C) 2020 Elsevier Ltd. All rights reserved.