Oscillation of impulsive neutral delay differential equations

In this paper, effective sufficient conditions for the oscillation of all solutions of impulsive neutral delay differential equations of the form (*) [x(t) - P(t)x(t - tau)]' + Q(t)\x(t - sigma)\(lambda)sgn x(t - sigma) = 0, (**) x(t(k)(+)) = b(k)x(t(k)), k - 1,2,... are established. Our results reveal the fact that the oscillatory properties of all solutions of Eqs. (*) and (**) may be caused by the impulsive perturbations (**) though the corresponding neutral delay differential equation without impulses, i.e., Eq. (*), admits a nonoscillatory solution. It is also seen that the oscillatory behavior of all solutions of Eq. (*) can be inherited by Eqs. (*) and (**) under certain impulsive perturbations (**). Some examples are also given to illustrate the applicability of the results obtained. (C) 2002 Elsevier Science (USA).