Asymptotic stability for the system of neutral delay differential equations

This paper deals with the asymptotic stability of the system of neutral delay differential equations in an angle which has fewer reports. Stability regions are presented geometrically as well as two criteria which are obtained through the evaluation of a harmonic function on the boundary of a certain region. Numerical experiments on various circumstances are shown to locate the specific region which can make the system unstable so as to exclude it from the whole complex‐plane.