Research

# Asymptotic behavior of an odd-order delay differential equation

Tongxing Li1 and Yuriy V Rogovchenko2*

Author Affiliations

1 Qingdao Technological University, Feixian, Shandong, 273400, P.R. China

2 Department of Mathematical Sciences, University of Agder, P.O. Box 422, Kristiansand, N-4604, Norway

For all author emails, please log on.

Boundary Value Problems 2014, 2014:107  doi:10.1186/1687-2770-2014-107

 Received: 29 January 2014 Accepted: 22 April 2014 Published: 9 May 2014

This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly credited.

### Abstract

We study asymptotic behavior of solutions to a class of odd-order delay differential equations. Our theorems extend and complement a number of related results reported in the literature. An illustrative example is provided.

MSC: 34K11.

##### Keywords:
asymptotic behavior; odd-order; delay differential equation; oscillation

### 1 Introduction

Professor Ivan Kiguradze is widely recognized as one of the leading contemporary experts in the qualitative theory of ordinary differential equations. His research has been partly summarized in the monograph written jointly with Professor Chanturia [1] where many fundamental results on the asymptotic behavior of solutions to important classes of nonlinear differential equations were collected. In particular, the Kiguradze lemma and Kiguradze classes of solutions are well known to researchers working in the area and are extensively used to advance the knowledge further.

In this tribute to Professor Kiguradze, we are concerned with the asymptotic behavior of solutions to an odd-order delay differential equation

(1.1)

where and is an odd natural number, is a ratio of odd natural numbers, , , , , , , , and .

By a solution of (1.1) we mean a function , , such that and satisfies (1.1) on . We consider only those extendable solutions of (1.1) that do not vanish eventually, that is, condition holds for all . We tacitly assume that (1.1) possesses such solutions. As customary, a solution of (1.1) is said to be oscillatory if it has arbitrarily large zeros on the ray ; otherwise, we call it non-oscillatory.

Analysis of the oscillatory and non-oscillatory behavior of solutions to different classes of differential and functional differential equations has always attracted interest of researchers; see, for instance, [1-19] and the references cited therein. One of the main reasons for this lies in the fact that delay differential equations arise in many applied problems in natural sciences, technology, and automatic control, cf., for instance, Hale [20]. In particular, (1.1) may be viewed as a special case of a more general class of higher-order differential equations with a one-dimensional p-Laplacian, which, as mentioned by Agarwal et al.[4], have applications in continuum mechanics.

Let us briefly comment on a number of closely related results which motivated our study. In [2,5-8,14], the authors investigated asymptotic properties of a third-order delay differential equation

Using a Riccati substitution, Liu et al.[11], Zhang et al.[16], and Zhang et al.[18] studied oscillation of (1.1) assuming that is even, , and

(1.2)

In the special case when , (1.1) reduces to a two-term differential equation

(1.3)

which was studied by Zhang et al.[17] who established the following result.

Theorem 1.1 ([[17], Corollary 2.1])

Let

and assume that. Suppose also that

and, for some,

Then every solution of (1.3) is either oscillatory or converges to zero as.

To the best of our knowledge, only a few results are known regarding oscillation of (1.1) for n odd. Furthermore, in this case the methods in [11,18] which employ Riccati substitutions cannot be applied to the analysis of (1.1). Therefore, the objective of this paper is to extend the techniques exploited in [17] to the study of (1.1) in the case when the integral in (1.2) is finite, that is, for all,

(1.4)

As usual, all functional inequalities considered in this paper are supposed to hold for all t large enough. Without loss of generality, we may deal only with positive solutions of (1.1), because under our assumption that γ is a ratio of odd natural numbers, if is a solution of (1.1), so is .

### 2 Main results

We need the following auxiliary lemmas.

Lemma 2.1Assume that (1.2) is satisfied and letbe an eventually positive solution of (1.1). Then there exists a sufficiently largesuch that, for all,

(2.1)

Proof Let be an eventually positive solution of (1.1). Then there exists a such that and for all . By virtue of (1.1),

Thus,

(2.2)

which means that the function

is decreasing for . Therefore, does not change sign eventually, that is, there exists a such that either or for all .

We claim that for all . Otherwise, there should exist a such that

and, for all ,

(2.3)

where

Inequality (2.3) yields

Integrating this inequality from to t, , we conclude that

Passing to the limit as and using (1.2), we deduce that

It follows now from the inequalities and that , which contradicts our assumption that . Finally, write (2.2) in the form

which implies that . This completes the proof. □

Lemma 2.2 (Agarwal et al.[3])

Assume that, is non-positive for all largetand not identically zero on. If, then for every, there exists asuch that

holds on.

Lemma 2.3 (Agarwal et al.[4])

The equation

whereis a quotient of odd natural numbers, , andis non-oscillatory if and only if there exist a numberand a functionsuch that, for all,

For a compact presentation of our results, we introduce the following notation:

Theorem 2.4Assume that

(2.4)

Then every solutionof (1.1) is either oscillatory or satisfies

(2.5)

provided that either

(i) (1.2) holds or

(ii) (1.4) is satisfied and, for some,

(2.6)

Proof Assume that (1.1) has a non-oscillatory solution which is eventually positive and such that

(2.7)

Case (i) By Lemma 2.1, we conclude that (2.1) holds for all , where is sufficiently large. It follows from Lemma 2.2 that

for every and for all sufficiently large t. Let

By virtue of (1.1), we conclude that is a positive solution of a differential inequality

However, it follows from the result due to Werbowski [[15], Corollary 1] that the latter inequality does not have positive solutions under the assumption (2.4), which is a contradiction. The proof of part (i) is complete.

Case (ii) Similar analysis to that in Lemma 2.1 leads to the conclusion that a non-oscillatory positive solution with the property (2.7) satisfies, for , either conditions (2.1) or

(2.8)

where is sufficiently large. Assume first that (2.1) holds. As in the proof of the part (i), one arrives at a contradiction with the condition (2.4). Suppose now that (2.8) holds. For , define a new function by

(2.9)

Then for . Since

we deduce that the function is decreasing. Thus, for,

(2.10)

Dividing both sides of (2.10) by and integrating the resulting inequality from t to T, we obtain

Letting and taking into account that and , we conclude that

Hence,

which yields

Thus, by (2.9), we conclude that

(2.11)

Differentiation of (2.9) yields

It follows now from (1.1) and (2.9) that

On the other hand, it follows from Lemma 2.2 that

for every and for all sufficiently large t. Therefore, (2.11) yields

(2.12)

Multiplying (2.12) by and integrating the resulting inequality from to t, we have

Let and . Using the fact that and the inequality

(see Zhang and Wang [[19], Lemma 2.3] for details) and the definition of φ, we derive from (2.11) that

which contradicts (2.6). This completes the proof for the part (ii). □

Remark 2.5 For a result similar to the one established in part (i) in Theorem 2.4, see also Zhang et al. [[16], Theorem 5.3].

Remark 2.6 For , Theorem 2.4 includes Theorem 1.1.

In the remainder of this section, we use different approaches to arrive at the conclusion of Theorem 2.4. First, we employ the integral averaging technique to replace assumption (2.6) with a Philos-type condition.

To this end, let . We say that a function belongs to the class if

and H has a non-positive continuous partial derivative with respect to the second variable satisfying the condition

for some function .

Theorem 2.7Letbe as in Theorem 2.4 and suppose that (1.4) and (2.4) hold. Assume that there exists a functionsuch that

(2.13)

for alland for some. Then the conclusion of Theorem 2.4 remains intact.

Proof Assuming that is an eventually positive solution of (1.1) that satisfies (2.7) and proceeding as in the proof of Theorem 2.4, we arrive at the inequality (2.12) which holds for all . Multiplying (2.12) by and integrating the resulting inequality from to t, we obtain

Let

and

Using the inequality

we obtain

which contradicts assumption (2.13). This completes the proof. □

Finally, we formulate also a comparison result for (1.1) that leads to the conclusion of Theorem 2.4.

Theorem 2.8Letbe as above, and assume that (1.4) and (2.4) hold. If a second-order half-linear ordinary differential equation

(2.14)

is oscillatory for some, then the conclusion of Theorem 2.4 remains intact.

Proof Assuming again that is an eventually positive solution of (1.1) that satisfies (2.7) and proceeding as in the proof of Theorem 2.4, we obtain (2.12) which holds for all . By virtue of Lemma 2.3, we conclude that (2.14) is non-oscillatory, which is a contradiction. The proof is complete. □

### 3 Example

The following example illustrates possible applications of theoretical results obtained in the previous section.

Example 3.1 For , consider the third-order differential equation

(3.1)

It is not difficult to verify that (1.4) holds and

Let . Then , , , and thus

for some . Hence, by Theorem 2.4, every solution of (3.1) is either oscillatory or satisfies (2.5). As a matter of fact, is a solution of this equation satisfying condition (2.5).

Remark 3.2 Note that Theorems 2.4, 2.7, and 2.8 ensure that every solution of (1.1) is either oscillatory or satisfies (2.5) and, unfortunately, these results cannot distinguish solutions with different behaviors. Since the sign of the derivative is not known, it is difficult to establish sufficient conditions which guarantee that all solutions of (1.1) are just oscillatory and do not satisfy (2.5). Neither is it possible to use the technique exploited in this paper for proving that all solutions of (1.1) satisfy (2.5). Therefore, these two interesting problems remain for future research.

### Competing interests

The authors declare that they have no competing interests.

### Authors’ contributions

Both authors contributed equally to this work and are listed in alphabetical order. They both read and approved the final version of the manuscript.

### Acknowledgements

The authors express their sincere gratitude to both anonymous referees for the careful reading of the original manuscript and useful comments that helped to improve the presentation of the results and accentuate important details.

### References

1. Kiguradze, IT, Chanturia, TA: Asymptotic Properties of Solutions of Nonautonomous Ordinary Differential Equations, Kluwer Academic, Dordrecht (1993)

2. Agarwal, RP, Aktas, MF, Tiryaki, A: On oscillation criteria for third order nonlinear delay differential equations. Arch. Math.. 45, 1–18 (2009)

3. Agarwal, RP, Grace, SR, O’Regan, D: Oscillation Theory for Difference and Functional Differential Equations, Kluwer Academic, Dordrecht (2000)

4. Agarwal, RP, Grace, SR, O’Regan, D: Oscillation Theory for Second Order Linear, Half-Linear, Superlinear and Sublinear Dynamic Equations, Kluwer Academic, Dordrecht (2002)

5. Baculíková, B, Džurina, J: Comparison theorems for the third-order delay trinomial differential equations. Adv. Differ. Equ.. 2010, (2010) Article ID 160761

6. Baculíková, B, Džurina, J, Rogovchenko, YuV: Oscillation of third order trinomial delay differential equations. Appl. Math. Comput.. 218, 7023–7033 (2012). Publisher Full Text

7. Džurina, J, Komariková, R: Asymptotic properties of third-order delay trinomial differential equations. Abstr. Appl. Anal.. 2011, (2011) Article ID 730128

8. Džurina, J, Kotorová, R: Properties of the third order trinomial differential equations with delay argument. Nonlinear Anal. TMA. 71, 1995–2002 (2009). Publisher Full Text

9. Grace, SR, Agarwal, RP, Pavani, R, Thandapani, E: On the oscillation of certain third order nonlinear functional differential equations. Appl. Math. Comput.. 202, 102–112 (2008). Publisher Full Text

10. Li, T, Rogovchenko, YuV, Tang, S: Oscillation of second-order nonlinear differential equations with damping. Math. Slovaca (2014, in press)

11. Liu, S, Zhang, Q, Yu, Y: Oscillation of even-order half-linear functional differential equations with damping. Comput. Math. Appl.. 61, 2191–2196 (2011). Publisher Full Text

12. Philos, ChG: Oscillation theorems for linear differential equations of second order. Arch. Math.. 53, 482–492 (1989). Publisher Full Text

13. Rogovchenko, YuV, Tuncay, F: Oscillation criteria for second-order nonlinear differential equations with damping. Nonlinear Anal.. 69, 208–221 (2008). Publisher Full Text

14. Tiryaki, A, Aktas, MF: Oscillation criteria of a certain class of third order nonlinear delay differential equations with damping. J. Math. Anal. Appl.. 325, 54–68 (2007). Publisher Full Text

15. Werbowski, J: Oscillations of first-order differential inequalities with deviating arguments. Ann. Mat. Pura Appl.. 140, 383–392 (1985). Publisher Full Text

16. Zhang, C, Agarwal, RP, Li, T: Oscillation and asymptotic behavior of higher-order delay differential equations with p-Laplacian like operators. J. Math. Anal. Appl.. 409, 1093–1106 (2014). Publisher Full Text

17. Zhang, C, Li, T, Sun, B, Thandapani, E: On the oscillation of higher-order half-linear delay differential equations. Appl. Math. Lett.. 24, 1618–1621 (2011). Publisher Full Text

18. Zhang, Q, Liu, S, Gao, L: Oscillation criteria for even-order half-linear functional differential equations with damping. Appl. Math. Lett.. 24, 1709–1715 (2011). Publisher Full Text

19. Zhang, S, Wang, Q: Oscillation of second-order nonlinear neutral dynamic equations on time scales. Appl. Math. Comput.. 216, 2837–2848 (2010). Publisher Full Text

20. Hale, JK: Theory of Functional Differential Equations, Springer, New York (1977)