`Abstract and Applied AnalysisVolume 2011, Article ID 265316, 19 pageshttp://dx.doi.org/10.1155/2011/265316`
Research Article

## Some Opial-Type Inequalities on Time Scales

College of Science Research Centre, King Saud University, P.O. Box 2455, Riyadh 11451, Saudi Arabia

Received 30 January 2011; Accepted 31 March 2011

Copyright © 2011 S. H. Saker. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

#### Abstract

We will prove some dynamic inequalities of Opial type on time scales which not only extend some results in the literature but also improve some of them. Some discrete inequalities are derived from the main results as special cases.

#### 1. Introduction

In 1960, Opial [1] proved the following inequality: where is absolutely continuous on and with a best constant . Since the discovery of Opial inequality, much work has been done, and many papers which deal with new proofs, various generalizations, and extensions have appeared in the literature. In further simplifying the proof of the Opial inequality which had already been simplified by Olech [2], Beescak [3], Levinson [4], Mallows [5], and Pederson [6], it is proved that if is real absolutely continuous on and with , then These inequalities and their extensions and generalizations are the most important and fundamental inequalities in the analysis of qualitative properties of solutions of different types of differential equations.

In recent decades, the asymptotic behavior of difference equations and inequalities and their applications have been and still are receiving intensive attention. Many results concerning differential equations carry over quite easily to corresponding results for difference equations, while other results seem to be completely different from their continuous counterparts. So, it is expected to see the discrete versions of the above inequalities. In fact, the discrete analogy of (1.1) which has been proved by Lasota [7] is given by where is a sequence of real numbers with and is the greatest integer function. The discrete analogy of (1.2) is proved in [8, Theorem  5.2.2] and given by where is a sequence of real numbers with . These difference inequalities and their generalizations are also important and fundamental in the analysis of the qualitative properties of solutions of difference equations.

Since the continuous and discrete inequalities are important in the analysis of qualitative properties of solutions of differential and difference equations, we also believe that the unification of these inequalities on time scales, which leads to dyanmic inequalities on time scales, will play the same effective act in the analysis of qualitative properties of solutions of dynamic equations. The study of dynamic inequalities on time scales helps avoid proving results twice: once for differential inequality and once again for difference inequality. The general idea is to prove a result for a dynamic inequality where the domain of the unknown function is the so-called time scale , which may be an arbitrary closed subset of the real numbers .

In this paper, we are concerned with a certain class of Opial-type dynamic inequalities on time scales and their extensions. If the time scale equals the reals (or to the integers), the results represent the classical results for differential (or difference) inequalities. A cover story article in New Scientist [9] discusses several possible applications. The three most popular examples of calculus on time scales are differential calculus, difference calculus, and quantum calculus (see Kac and Cheung [10]), that is, when ,  , and , where . For more details of time scale analysis we refer the reader to the two books by Bohner and Peterson [11, 12] which summarize and organize much of the time scale calculus.

In the following, we recall some of the related results that have been established for differential inequalities and dynamic inequalities on time scales that serve and motivate the contents of this paper. For a generalization of (1.1), Beescak [3] proved that if is an absolutely continuous function on with , then where is positive and continuous function with , and if , then Yang [13] simplified the Beesack proof and extended the inequality (1.5) and proved that if is an absolutely continuous function on with , then where is a positive and continuous function with and is a positive, bounded, and nonincreasing function on .

Hua [14] extended the inequality (1.2) and proved that if is an absolutely continuous function with , then where is a positive integer. We mentioned here that the results in [14] fail to apply for general values of .

Maroni [15] generalized (1.5) and proved that if is an absolutely continuous function on with , then where , and .

Boyd and Wong [16] extended the inequality (1.8) for general values of and proved that if is an absolutely continuous function on with , then where and are nonnegative functions in and is the smallest eigenvalue of the boundary value problem with and for which in .

Yang [13] extended the inequality (1.8) and proved that if is an absolutely continuous function on with , and , then Yang [17] extended the inequality (1.12) and proved that if is a positive, bounded function and is an absolutely continuous on with , ,, then However, as mentioned by Beesack and Das [18], the inequalities (1.12) and (1.13) are sharp when but are not sharp for . Considering this problem, Beesack and Das [18] extended and improved the inequalities (1.12) and (1.13) when or or both. In fact, the extensions dealt with integral inequalities of the form where the functions are nonnegative measurable functions on , is absolutely continuous on ,  , and either or , with a sharp constant depends on , and . For applications of the inequality (1.14) on zeros of differential equations, we refer the reader to the paper [19].

However, the study of dynamic inequalities of Opial types on time scales is initiated by Bohner and Kaymakçalan [20], and only recently received a lot of attention and few papers have been written, see [2024] and the references cited therein. For contribution of different types of inequalities on time scales, we refer the reader to the papers [2528] and the references cited therein.

Throughout the paper, we denote , where the forward jump operator is defined by . By is rd-continuous, we mean is continuous at all right-dense points and at all left-dense points left hand limits exist (finite). The graininess function is defined by . Also if has a left-scattered maximum , otherwise . We will assume that , and define the time scale interval by .

In [20], the authors extended the inequality (1.1) on time scales and proved that if is delta differentiable with , then Also in [20] the authors extended the inequality (1.7) of Yang and proved that if and are positive rd-continuous functions on ,    nonincreasing and is delta differentiable with , thenKarpuz et al. [21] proved an inequality similar to the inequality (1.16) replaced by of the form where is a positive rd-continuous function on, is delta differentiable with , and We note that when , we have , and then the inequality (1.15) becomes the opial inequality (1.2). When , we have ,   and the inequality (1.15) reduces to the inequality which is different from the inequality (1.4). This means that the extensions obtained by Bohner and Kaymakçalan [20] and Karpuz et al. [21] do not give a unification of differential and difference inequalities. So, the natural question now is: if it possible to find new Opial dynamic inequalities which contains (1.2) and (1.4) as special cases? One of our aims in this paper is to give an affirmative answer to this question.

Srivastava et al. [22] extended the Maroni inequality on a time scale and proved that if is delta differentiable with , then where and are positive rd-continuous functions on , such that is bounded and decreasing, ,   and . For the interested reader, it would be interesting to extend the inequality (1.20) with the term replaced by .

Wong et al. [23] and Srivastava et al. [24] extended the Yang inequality on a time scale and proved that if is a positive rd-continuous function on , we have where is delta differentiable with . But according to Beesack and Das [18], the inequality (1.21) is only sharp when . So, the natural question now is: if it is possible to prove new inequality of type (1.21) with two different functions and , instead of with a best constant? One of our aims in this paper is to give an affirmative answer to this question. Also one of our motivations comes from the fact that the inequality of type (1.21) cannot be applied on the study of the distribution of the generalized zeros of the general dynamic equation

since this study needs an inequality with two different functions instead of a single function.

The paper is organized as follows. First, we will extend the inequality (1.10) on a time scale which gives a connection between a dynamic Opial-type inequality and a boundary value problem on time scales. Second, we prove some new Opial-type inequalities on time scales with best constants of type (1.14). The main results give the affirmative answers of the above posed questions. Throughout the paper, some special cases on continuous and discrete spaces are derived and compared by previous results.

#### 2. Main Results

In this section, we will prove the main results, and this will be done by making use of the Hölder inequality (see [11, Theorem  6.13]) where and   and , and the inequality (see [29, page 39]) We also need the product and quotient rules for the derivative of the product and the quotient (where of two differentiable functions and and the formula which is a simple consequence of Keller's chain rule [11, Theorem  1.90]. We will assume that the boundary value problem has a solution such that on the interval , where are nonnegative rd-continuous functions on .

Now, we are ready to state and prove one of our main results in this section. We begin with an inequality of Opial type which gives a connection with boundary value problems (2.5) on time scales.

Theorem 2.1. Let be a time scale with and let be nonnegative rd-continuous functions on such that (2.5) has a solution for some . If is delta differentiable with , then for ,

Proof. Let be a solution of the boundary value problem (2.5) and denote Using the inequality (2.2) and substituting for and for , we obtain Multiplying this inequality by , integrating from 0 to , and using the fact that , we have By the chain rule (2.4) and the fact that , we obtain Noting that if is rd-continuous and , we see that From the definition of , we see that Substituting into (2.10), we see that Substituting (2.13) into (2.9), we have Integrating by parts and using the assumption , we see that From (2.14) and (2.15), we see that From the definition of the function , we see that From this and (2.3), we obtain In view of (2.5) and (2.18), we get that Using the fact that and the chain rule (2.4), we see that It follows from (2.19) and (2.20) that From (2.21) and (2.16), we have This implies that Using the integration by parts again and using (2.13), we see that Substituting (2.24) into (2.23), we have From this, we obtain This implies that which is the desired inequality (2.6) after replacing by and by . The proof is complete.

Remark 2.2. Note that when , we have and, so that and then (2.6) becomes the inequality (1.10) that has been proved by Boyed and Wong [16]. Note also that the inequality (2.6) can be applied for different values of and , and this will left to the interested reader.

When , then (2.6) reduces to the following discrete inequality.

Corollary 2.3. Assume that and be nonnegative sequences such that the boundary value problem has a solution such that on the interval for some . If is a sequence of real numbers with , then for ,

Next, in the following we will prove some Opial-type inequalities on time scales which can be considered as the extension of the inequality (1.14) obtained by Beesack and Das [18].

Theorem 2.4. Let be a time scale with and positive real numbers such that , and let be nonnegative rd-continuous functions on such that . If is delta differentiable with (and does not change sign in , then where

Proof. Let Now, since is nonnegative on , it follows from the Hölder inequality (2.1) (assuming that the integrals exist) with that Then, for , we get that Setting We see that , and This gives us Thus, if is a nonnegative on , we have from (2.35) and (2.38) that This implies that Supposing that the integrals in (2.40) exist and again applying the Hölder inequality (2.1) with indices and , we have From (2.37), the chain rule (2.4), and the fact that , we obtain Substituting (2.42) into (2.41) and using the fact that , we have Using (2.36), we have from the last inequality that which is the desired inequality (2.30). The proof is complete.

Here, we only state the following theorem, since its proof is the same as that of Theorem 2.4, with replaced by .

Theorem 2.5. Let be a time scale with and positive real numbers such that , and let be nonnegative rd-continuous functions on such that . If is delta differentiable with , (and does not change sign in , then one has where

In the following, we assume that there exists which is the unique solution of the equation

where and are defined as in Theorems 2.4 and 2.5. Note that since

then the proof of the following theorem will be a combination of Theorems 2.4 and 2.5 and due to the limited space we omit the details.

Theorem 2.6. Let be a time scale with and positive real numbers such that and , and let be nonnegative rd-continuous functions on such that . If is delta differentiable with , (and does not change sign in , then one has

For in (2.30), we obtain the following special case from Theorem 2.4, which improves the inequality (1.21) obtained by Wong et al. [23].

Corollary 2.7. Let be a time scale with and positive real numbers such that , and let be a nonnegative rd-continuous function on such that . If is delta differentiable with , (and does not change sign in , then one has where

From Theorems 2.5 and 2.6 one can derive inequalities similar to the inequality in (2.50) by setting . The details are left to the reader.

On a time scale , we note as a consequence from the chain rule (2.4) that

This implies that

From this and (2.51) with , one gets that So setting in (2.50) and using (2.54), one has the following inequality.

Corollary 2.8. Let be a time scale with and be positive real numbers such that . If is delta differentiable with , (and does not change sign in , then, one has

Remark 2.9. Note that when , the inequality (2.55) becomes which gives an improvement of the inequality (1.13).

When , we have form (2.55) the following discrete Opial-type inequality.

Corollary 2.10. Assume that be positive real numbers such that and   a nonnegative real sequence. If is a sequence of real numbers with , then

The inequality (2.55) has immediate application to the case where . Choose and apply (2.51) to and and then add we obtain the following inequality.

Corollary 2.11. Let be a time scale with and positive real numbers such that . If is delta differentiable with , then one has

From this inequality, we have the following discrete Opial-type inequality.

Corollary 2.12. Assume that be positive real numbers such that . If is a sequence of real numbers with , then

By setting in (2.58), we have the following Opial type inequality on a time scale.

Corollary 2.13. Let be a time scale with . If is delta differentiable with , then one has

When and , we have from (2.60) the following inequalities.

Corollary 2.14. If is differentiable with , then one has

Corollary 2.15. If is a sequence of real numbers with , then

#### Acknowledgments

This project was supported by King Saud University, Dean-ship of Scientific Research, College of Science Research Centre.

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