Abstract
We established some new -conformable dynamic inequalities of Hardy–Knopp type. Some new generalizations of dynamic inequalities of -conformable Hardy type in two variables on time scales are established. Furthermore, we investigated Hardy’s inequality for several functions of -conformable calculus. Our results are proved by using two-dimensional dynamic Jensen’s inequality and Fubini’s theorem on time scales. When , then we obtain some well-known time-scale inequalities due to Hardy. As special cases, we derived Hardy’s inequality for and . Symmetry plays an essential role in determining the correct methods to solve dynamic inequalities.
1. Introduction
The renowned discrete Hardy’s inequality [1] states that:
Theorem 1.
If is a nonnegative real sequence and , then
Hardy discovered this inequality while attempting to sketch an easier proof of Hilbert’s inequality for double series, which was known at that time.
Using the calculus of variations, Hardy himself in [2] gave the following integral analogous of inequality (1).
Theorem 2.
If ϕ is a nonnegative integrable function over a finite interval such that and , then
It is worth mentioning that inequalities (1) and (2) are sharp in the sense that the constant in each of them cannot be replaced by a smaller one.
In [3], Hardy and Littlewood extended inequality (1) and obtained the following two discrete inequalities.
Theorem 3.
Let be a nonnegative real sequence.
Theorem 4.
Let ϕ be a nonnegative integrable function ϕ on .
- ()
- If and , then
- ()
- If and , then
The reverse of inequality (2) was proven by Hardy and Littlewood in [3]. Their result can be written as:
Theorem 5.
If and ϕ is a nonnegative integrable function on such that , then
In the same paper [3], the authors proved the following sharp inequality.
Theorem 6.
If and ϕ is a nonnegative integrable function on such that , then
which by a trivial transformation can be written as
The discrete version of inequality (9) was given in [4] as follows:
Theorem 7.
If is a nonnegative real sequence and , then
Hardy [5] generalized (1) and proved the following result.
Theorem 8.
If for and , then
The study of Hardy type inequalities has attracted the attention of many researchers. Over several decades, many generalizations, extensions, and refinements have been made to the above inequalities; we refer the reader to the papers [1,2,5,6,7,8,9,10], the books [4,11], and the references cited therein.
Time-scale calculus with the objective to unify discrete and continuous analysis was introduced by S. Hilger [12]. For additional subtleties on time scales, we direct the peruser to the books by Bohner and Peterson [13,14].
In [15], Řehák has given the time scales version of Hardy’s inequality as follows:
Theorem 9.
Let be a time scale and for .
unless .
Furthermore, if as , then inequality (12) is sharp.
In [16], Saker and O’Regan established a generalization of Řehák’s result in the following form.
Theorem 10.
Let be time scale and Let
for any and define
for any . Then
and
Theorem 11.
Recently, in 2017, Agarwal et al. [17] gave the inequality.
Theorem 12.
Suppose is a time scale such that . Further, assume η is a nonincreasing nonnegative function on . If , then
In 2020, El-Deeb et al. [18] established a generalization of inequality (15).
Theorem 13.
Suppose that is a time scale with . Moreover, assume that η and λ are nonnegative rd-continuous functions on with η nonincreasing. If and , then
where
In 2020, Saker [19] proved the following theorem.
Theorem 14.
Assume that is a time scale with If and then
If and then
where
In [20], Ozkan and Yildirim gave the following result among many other results.
Theorem 15.
Let and such that the delta integral converges. If and is convex, then
Benkhettou et al. [21] introduced a conformable calculus on an arbitrary time scale, which is a natural extension of the conformable calculus.
We define the forward jump operator by
and the backward jump operator is defined by
Definition 1.
Let , and For we define to be the number (provided it exists) with the property that, given any there is a δ-neighborhood of such that
for all We call the conformable derivative of η of order α at t, and we define a conformable derivative on at as
Remark 1.
If , then we obtain from Definition 1 the delta derivative of time scales. The conformable derivative of order zero is defined by the identity operator .
Theorem 16.
Let and be a time scale. Assume and . The following properties hold.
- (i)
- If η is conformable differentiable of order α at then η is continuous at t;
- (ii)
- If η is continuous at t and t is right-scattered, then η is conformable differentiable of order α at t with
- (iii)
- If t is right-dense, then η is conformable differentiable of order α at t if and only if the limit exists as a finite number. In this case,
- (iv)
- If η is differentiable of order α at then
The conformable derivative has the following properties.
Theorem 17.
Assume are conformable differentiable of order then the following properties hold:
- (i)
- The sum is conformable differentiable with
- (ii)
- For any is conformable differentiable with
- (iii)
- If η and ξ are continuous, then the product is conformable differentiable with
- (iv)
- If η is continuous, then is conformable differentiable withvalid at all points for which ;
- (v)
- If η and ξ are continuous, then is conformable differentiable withvalid for all for which
Definition 2.
Let be regulated function. Then, the α-conformable integral of is defined by
Definition 3.
Suppose is a regulated function. Denote the indefinite α-conformable integral of η of order as follows: . Then, for all , we define the Cauchy α-conformable integral by
A few years ago, by using conformable calculus, a lot of papers were published on conformable inequalities and several authors investigated several new conformable inequalities of Hardy type. For example, in 2020, Saker et al. [22] gave an -conformable version of Theorems 10 and 11 on time scales as follows:
Theorem 18.
Let be time scales and define
If and
then
Theorem 19.
Let be time scales and and define
If and
then
In 2021, Zakarya et al. [23] gave an -conformable version of Theorem 14 on time scales as follows:
Theorem 20.
Assume that are time scales with and Define
Then,
Theorem 21.
Assume that are time scales with and Define
such that
Then,
As the same proof of Theorem 10, we can write the conformable version as follows:
Theorem 22.
Let and define, for ,
If , then
In this paper, we prove some generalizations of Hardy type dynamic inequalities that were given recently by Ozkan and Yildirim in [20]. The obtained results extend some known Hardy type integral inequalities and unify and extend some continuous inequalities and their corresponding discrete analogues. The paper is arranged as follows: In Section 2, we state and prove the main results. In Section 3, we state the conclusion.
Lemma 1.
[24] (Fubini’s Theorem on time scales) Let ψ be bounded and Δ-integrable over and suppose that the single integrals
exist for each and for each , respectively. Then, the iterated integrals
exist and the equality
holds.
Lemma 2.
[25] (Dynamic Jensen’s Inequality) Suppose that with . Further, let and . If is convex, then
We need the following lemma, which gives a two-dimensional dynamic Jensen’s inequality, in the proof of our main results.
Lemma 3
([25]). Suppose that with and . Further, let and . If is convex, then
2. Main Results
Theorem 23.
Let and such that the delta integral
converges. If and is convex, then
Proof.
Employing the dynamic Jensen inequality (20) and Fubini’s theorem on time scales, we obtain
which is our desired result. □
Remark 2.
If we put , in Theorem 23, then we recapture Theorem 15.
Below, we present various applications of Theorem 23.
- ()
- ()
- ()
- ()
- If and in Theorem 23, then inequality (22) reduces to
- ()
- If and in Theorem 23, then inequality (22) reduces to
- ()
Theorem 24.
Suppose that and . If is convex, then
Proof.
Using the two-dimensional dynamic Jensen inequality (21) and Fubini’s theorem on time scales, we get
This concludes the proof. □
Remark 3.
If we put , and in Theorem 24, then we recapture ([20], Theorem 3.2).
- ()
- In Theorem 24, if we take , where is a constant, then we have
- ()
- In Theorem 24, if we take and replace by , then we have
- ()
- If and in Theorem 24, then inequality (28) reduces to
- ()
- If and in Theorem 24, then inequality (28) reduces to
- ()
Our aim in the following theorem is to establish a dynamic Hardy inequality for several functions.
Theorem 25.
Assume that and . Define and for . If , then
Proof.
Utilizing the discrete Jensen inequality, we have
and thus
Multiplying both sides of (31) by and integrating the resulting inequality over ℑ from a to ∞ yield
Applying inequality (19) to the right-hand side of the last inequality implies
The proof is complete. □
Remark 4.
If we put and in Theorem 25, then we recapture [20] (Theorem 1.4).
Below, we present various applications of Theorem 25.
- ()
- If and in Theorem 25, then inequality (30) reduces towhere and for .
- ()
- ()
3. Conclusions, Discussions, and Future Work
There are several applications for Hardy type inequalities and they are subject to strong research; see [3,7,15,16]. In this manuscript, by employing the dynamic Jensen’s inequality and Fubini’s theorem on time scales, we extended a number of -conformable Hardy type inequalities to a general time scale. Several new Hardy type inequalities were proved. The results extend several dynamic inequalities known in the literature, being new even in the discrete and continuous domains. In future work, we will generalize these results by using -conformable fractional calculus.
Author Contributions
Conceptualization, A.A.E.-D., A.A.E.-B., J.A. and K.N; formal analysis, A.A.E.-D., A.A.E.-B., J.A. and K.N.; investigation, A.A.E.-D., A.A.E.-B., J.A. and K.N.; writing–original draft preparation, A.A.E.-D., A.A.E.-B., J.A. and K.N.; writing–review and editing, A.A.E.-D., A.A.E.-B., J.A. and K.N. All authors have read and agreed to the published version of the manuscript.
Funding
This research received no external funding.
Data Availability Statement
Not applicable.
Conflicts of Interest
The authors declare no conflict of interest.
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