Existence results on positive periodic solutions of forced functional difference equations and applications

The forced functional difference equationΔx(n)=-a(n)x(n)+λh(n)f(n,x(n),x(n-τ1(n)),…,x(n-τm(n)))+r(n),n∈Zis investigated. Easily verifiable sufficient conditions are established for the existence of positive periodic solutions. Applications are given to illustrate the main results.