Asymptotic Periodicity of Delay Differential Equations

In this paper, the authors consider the forced delay differential equation x9 t. qa t.x t. qb t.x tyt . sf t., E. where a, b, and f are continuous v-periodic functions, b has fixed sign, and t )0. They give sufficient conditions for E. to have periodic solutions. In a second result, they give sufficient conditions for every solution of E. to asymptotically approach a periodic solution of the equation.