Multiple Periodic Solutions of Nonautonomous Delay Differential Equations

Abstract

In this paper, we consider a nonautonomous high-order delay differential equation with [Formula: see text] lags. The [Formula: see text]-periodic orbits are obtained by using the variational method and a new [Formula: see text] index theory. This is a new type of nonautonomous delay differential equation compared with all existing ones. An example is given to demonstrate our main results.