Positive periodic solutions for a neutral delay Lotka-Volterra system

Applying a fixed point theorem of strict-set-contraction, some new criteria are established for the existence of positive periodic solutions for a class of neutral delay Lotka-Volterra systems: x(i)' (t) = x(i)(t) [r(i)(t) - Sigma(n)(j=1) a(ij)(t)x(j)(t) - Sigma(n)(j=1) b(ij)(t)x(j)(t-tau(ij)(t)) - Sigma(n)(j=1) c(ij)(t)x(j)'(t-sigma(ij)(t))], i = 1,2, ..., n. Compared to known results, our main generalization is that delays of the derivatives are not assumed to be constants, and our results are more easily verifiable. (C) 2006 Elsevier Ltd. All rights reserved.