On Nonoscillation of Mixed Advanced-Delay Differential Equations with Positive and Negative Coefficients

For a mixed (advanced--delay) differential equation with variable delays and coefficients $$\dot{x}(t) \pm a(t)x(g(t)) \mp b(t)x(h(t)) = 0, t\geq t_0$$ where $$a(t)\geq 0, b(t)\geq 0, g(t)\leq t, h(t)\geq t$$ explicit nonoscillation conditions are obtained.Comment: 17 pages; 2 figures; to appear in Computers & Mathematics with Application

Oscillations of advanced difference equations with variable arguments

Consider the first-order advanced difference equation of the form \begin{equation*} \nabla x(n)-p(n)x(\mu (n))=0\text{, }\ n\geq 1\, [\Delta x(n)-p(n)x(\nu (n))=0, n\geq 0], \end{equation*} where $\nabla$ denotes the backward difference operator $\nabla x(n)=x(n)-x(n-1)$, $\Delta$ denotes the forward difference operator $\Delta x(n)=x(n+1)-x(n)$, $\left\{ p(n)\right\}$ is a sequence of nonnegative real numbers, and $\left\{ \mu (n)\right\}$ $\ \left[ \left\{ \nu (n)\right\} \right]$ is a sequence of positive integers such that \begin{equation*} \mu (n)\geq n+1\ \text{ for all }n\geq 1\, \left[ \nu (n)\geq n+2 \ \text{ for all }n\geq 0\right] \text{.} \end{equation*} Sufficient conditions which guarantee that all solutions oscillate are established. The results obtained essentially improve known results in the literature. Examples illustrating the results are also given

Numerical treatment of oscillatory delay and mixed functional differential equations arising in modelling

The pervading theme of this thesis is the development of insights that contribute to the understanding of whether certain classes of functional differential equation have solutions that are all oscillatory. The starting point for the work is the analysis of simple (linear autonomous) ordinary differential equations where existing results allow a full explanation of the phenomena. The Laplace transform features as a key tool in developing a theoretical background. The thesis goes on to explore the corresponding theory for delay equations, advanced equations and functional di erential equations of mixed type. The focus is on understanding the links between the characteristic roots of the underlying equation, and the presence or otherwise of oscillatory solutions. The linear methods are used as a class of numerical schemes which lead to discrete problems analogous to each of the classes of functional differential equation under consideration. The thesis goes on to discuss the insights that can be obtained for discrete problems in their own right, and then considers those new insights that can be obtained about the underlying continuous problem from analysis of the oscillatory behaviour of the analogous discrete problem. The main conclusions of the work are some semi-automated computational approaches (based upon the Principle of the Argument) which allow the prediction of oscillatory solutions to be made. Examples of the effectiveness of the approach are provided, and there is some discussion of its theoretical basis. The thesis concludes with some observations about further work and some of the limitations of existing analytical insights which restrict the reliability with which the approach developed can be applied to wider classes of problem