Existence of multiple positive periodic solutions for functional differential equations

In our paper, by employing Krasnoselskii fixed point theorem, we investigate the existence of multiple positive periodic solutions for functional differential equations ˙x(t) = A t,x(t) x(t)+ λf (t , xt ), where λ>0 is a parameter. Some easily verifiable sufficient criteria are established. © 2006 Elsevier Inc. All rights reserved.