Some general theorems are available about the existence and global continuationof periodic solutions in symmetric delay differential equations.
关于对称时滞微分方程中的周期解的存在性和全局持续存在性，现在已有一些一般性的理论。
2
By using the continuation theorem of topology degree theory and properties of nonsingular M-matrix, we obtain sufficient conditions for the existence of positive periodic solutions of this system.
利用拓扑度理论中的连续定理以及M -矩阵的性质获得了该系统正周期解存在的充分条件。
3
Sufficient conditions for the existence of positive periodic solutions are established by applying the continuation theorem of coincidence degree theory.