Multiple positive periodic solutions of nonlinear functional differential system with feedback control ✩

In this paper, we employ Avery–Henderson fixed point theorem to study the existence of positive periodic solutions to the following nonlinear nonautonomous functional differential system with feedback control: dx dt =−r(t)x(t)+ F(t,xt,u(t −δ(t ))), du dt =−h(t)u(t)+ g(t)x(t − σ (t )). We show that the system above has at least two positive periodic solutions under certain growth condition imposed on F.  2003 Elsevier Inc. All rights reserved