Abstract
We prove new Hardy–Copson-type -nabla fractional dynamic inequalities on time scales. Our results are proven by using Keller’s chain rule, the integration by parts formula, and the dynamic Hölder inequality on time scales. When , then we obtain some well-known time-scale inequalities due to Hardy. As special cases, we obtain new continuous and discrete inequalities. Symmetry plays an essential role in determining the correct methods to solve dynamic inequalities.
1. Introduction
A great number of dynamic Hardy type inequalities on time scales have been established by many researchers who were motivated by some applications [1,2,3]. Additionally, over several decades, many generalizations, extensions, and refinements of other types of dynamic inequalities have been studied; we refer the reader to the papers [4,5,6,7,8].
In 1920, Hardy [9] established the following renowned discrete inequality.
Theorem 1.
If is a non-negative real sequence and , then
In 1925, using the calculus of variations, Hardy himself in [10] gave the integral analogous of inequality (1) as follows:
Theorem 2.
If f is a non-negative continuous function on and , then
Copson [11] improved inequality (1) by replacing the arithmetic mean of a sequence by a weighted arithmetic mean in the following manner: Let and for all ℓ. If then
where and if then
Hardy–Copson inequalities have been developed by Bennett as follows: Let and for all ℓ and . If then
and
where and .
If then
and
Then, the continuous version of the inequalities (3) (or (7)) and (6) (or (8)) established by Copson [12], respectively, are as follows: Let and be non-negative functions and , . If , then
and if , then
Other refinements of continuous Hardy–Copson inequalities, which are generalizations of (9) and (10), respectively, have been introduced by Pacarić and Hanjs as follows: Let and be non-negative functions and , .
If then
and if then
A time scale is an arbitrary non-empty closed subset of the real numbers . We assume throughout that has the topology that it inherits from the standard topology on the real number . For more details on time-scales calculus, see [13,14]. We define the forward jump operator by
and the backward jump operator is defined by
In the previous two definitions, we set (i.e., if is the minimum of , then ) and (i.e., if is the maximum of , then ), where ∅ is the empty set.
We introduce the nabla derivative of a function at a point , as follows:
Definition 1.
Let be a function, and let . We define as the real number (provided it exists) with the property that for any , there exists a neighborhood N of t (i.e., for some ), such that
We say that is the nabla derivative of f at t.
Definition 2.
We say that a function is a nabla antiderivative of if for all . In this case, the nabla integral of f is defined by
Now, we introduce the set of all ld-continuous functions in order to find a class of functions that have nabla antiderivatives.
Definition 3
(Ld-Continuous Function). We say that the function is ld-continuous if it is continuous at all left-dense points of and its right-sided limits exist (finite) at all right-dense points of .
Theorem 3
(Existence of Nabla Antiderivatives). Every ld-continuous function possess a nabla antiderivative.
In 2021, Kayar et al. [15], established the time-scale version unification of discrete and continuous Bennett–Leindler inequalities (10) and (11), as in the following theorem.
Theorem 4.
Assume that is a time scale with . Moreover, suppose that ϕ and g are non-negative, ld-continuous, ∇-differentiable, and locally nabla integrable functions. Set
Assume that and . Suppose that there exists , such that for . If , and are real constants, then
- (i)
- (ii)
- (iii)
- (iv)
- (v)
- (vi)
Rahmat introduced a new nabla conformable calculus in his recent paper [16]. He presents the following basic definitions and concepts.
Definition 4.
Let and . The generalized time-scale power function for is defined by
and its inverse function is then given by
We use the convention for all .
Definition 5.
Given a function and f is -nabla differentiable at if it is nabla differentiable at ς, and its -nabla derivative is defined by
where the function , as defined in (15). If exists in some interval then we define
if the exists. Moreover, we call f as -nabla differentiable on , provided exists for all . The function is then called the -nabla derivative of f on .
Next, we provide the -nabla derivatives of sums, products, and quotients of -nabla differentiable functions.
Theorem 5.
Assume are -nabla differentiable at . Then:
- (i)
- The sum is -nabla differentiable at t, with
- (ii)
- For all then is -nabla differentiable at t with
- (iii)
- The product is -nabla differentiable at t, with
- (iv)
- If then is -nabla differentiable at t, with
Lemma 1.
Let and assume that is a continuously differentiable function. Then, is -nabla differentiable and satisfies
Lemma 2.
Let . Assume is continuous and -nabla differentiable of order γ at where and is continuously differentiable. Then, there is c in the real interval , such that
Lemma 3.
Suppose that , where . If ξ are conformable -nabla fractional differentiable and then
Definition 6.
Assume that , and then we say that f is -nabla integrable on interval if the following integral:
exists and is finite.
For the case we have the classical conformable integral as defined in [17], namely
For we have a new conformable fractional h-sum given by
For we have a new conformable fractional q-sum given by
Theorem 6.
Let and . Then, for any ld-continuous function there exists a function , such that
The function F is called an -nabla antiderivative of f.
Lemma 4
([18]) (Hölder inequality for the -nabla derivative). Let , where . If and then
where and . This inequality is reversed if and if or .
Here, we prove the new Hardy–Copson-type dynamic via the -nabla-conformable calculus on time scales. Our inequalities have a completely new form and may be considered as extensions of [15]. As special cases, we obtain some new continuous and discrete inequalities of the Hardy-type, generalizing those obtained in the literature.
The paper is organized as follows. The original results are given and proven in Section 2. In Section 3, we stated the discussion of the results. We end with Section 4, the conclusion.
Now, we are ready to state and to prove our main results. Throughout the following, we assumed that the time-scale is unbounded above.
2. Main Results
Theorem 7.
Assume that is a time scale with and . Moreover, suppose that g and ϕ are non-negative -nabla fractional differentiable and locally integrable functions on . Set and and assume that and . Suppose that there exists , such that for . If , and are real constants, then
- (i)
- (ii)
- (iii)
- (iv)
- (v)
- (vi)
Proof.
- (i)
- By using the integration by parts to the left-hand side of inequality (25), we have and it becomeswhere . By using and one can haveBy chain rule, and using we obtainSince and by chain rule, we getTherefore,
- (ii)
- SinceApplying the Hölder inequality with the constants p and to the right-hand side of above equation leads to the inequalitytherefore,which is the desired inequality (26).
- (iii)
- (iv)
- Now, by using the Hölder inequality with the constants we get thatthus,
- (v)
- By using the integration by parts to the left-hand side of inequality (29), we have and which becomeswhere . By using and one can haveBy following the procedure in the proof of , we arrive at inequality (34) aswhich implies . Then, we obtain that
- (vi)
- SinceApplying the Hölder inequality with the constants p and to the right-hand side of the above equation leads to the inequalitytherefore,which is the desired inequality (30).
□
Remark 1.
In Theorem 7, if we take , then we get Theorem 4.
Corollary 1.
In Theorem 7, if we take and , then we get
- (i)
- (ii)
where
Remark 2.
In inequality (45), if we take and , we get inequality (9).
Remark 3.
In inequality (45), if we take and we get inequality (11).
Corollary 2.
where
In Theorem 7, if we take , then we get
- (i)
- (ii)
- (iii)
- (iv)
- (v)
- (vi)
Theorem 8.
Assume that is a time scale with and . Moreover, suppose that g and ϕ are non-negative -nabla fractional differentiable and locally integrable functions on . Set and and assume that and . Suppose that there exists , such that for . If , and are real constants, then
- (i)
- (ii)
- (iii)
- (iv)
- (v)
- (vi)
Proof.
- (i)
- By using the integration by parts to the left-hand side of inequality (46), we have and it becomeswhere . By using and one can haveBy chain rule, and by using we obtainSince and by chain rule, we getTherefore,Substituting (54) and (56) into (53) leads towhich is the desired result (46).
- (ii)
- SinceApplying the Hölder inequality with the constants p and to the right-hand side of the above equation leads to inequalitytherefore,which is the desired inequality (47).
- (iii)
- To obtain inequality (48), we usein inequality (47). Then, the desired inequality (48) can be proven directly.
- (iv)
- In order to obtain inequality (49), we use inequality (46) and the constant as follows.Now, by using the Hölder inequality with the constants we get thatthus,
- (v)
- By using the integration by parts to the left-hand side of inequality (50), we have and it becomeswhere . By using and one can haveBy following the procedure in the proof of , we arrive at inequality (55) aswhich implies . Then, we obtain that
- (vi)
- Since,Applying the Hölder inequality with the constants p and to the right-hand side of the above equation leads to the inequalitytherefore,which is the desired inequality (51).
□
Corollary 3.
In Theorem 8, if we take , then we get
- (i)
- (ii)
- (iii)
- (iv)
- (v)
- (vi)
where
which is Theorem 3.8 in [15].
Corollary 4.
where
In Theorem 8, if we take and , then we get
- (i)
- (ii)
Corollary 5.
In Theorem 8, if we take , then we get
- (i)
- (ii)
- (iii)
- (iv)
- (v)
- (vi)
where
Theorem 9.
Assume that is a time scale with and . Moreover, suppose that g and ϕ are non-negative -nabla fractional differentiable and locally integrable functions on . Set and and assume that and . If and are real constants, then
- (i)
- (ii)
Proof.
- (i)
- By using the integration by parts to the left-hand side of inequality (67), we have and and it becomeswhere . By using and one can haveBy chain rule, and by using we obtainSince and by chain rule, we getTherefore,Substituting (71) and (74) into (70) leads towhich is the desired result (67).
- (ii)
- Employing the same procedure of the proof of of Theorem 7, we obtain the desired result (68).
□
Corollary 6.
In Theorem 9, if we take , we get that
- (i)
- (ii)
where
which is Theorem 3.13 in [15].
Corollary 7.
In Theorem 9, if we take , we get that
- (i)
- (ii)
where
Corollary 8.
In Theorem 9, if we take , we get that
- (i)
- (ii)
where
Theorem 10.
Assume that is a time scale with and . Moreover, suppose that g and ϕ are non-negative -nabla fractional differentiable and locally integrable functions on . Set and and assume that and . If and are real constants, then
- (i)
- (ii)
Proof.
- (i)
- By using the integration by parts to the left-hand side of inequality (75), we have and it becomeswhere . By using and one can haveBy chain rule, and using we obtainSince and by chain rule, we getTherefore,
- (ii)
- Employing the same procedure of the proof of of Theorem 7, we obtain the desired result (76).
□
Corollary 9.
In Theorem 10, if we take , we get that
- (i)
- (ii)
where
which is Theorem 3.19 in [15].
Corollary 10.
In Theorem 10, if we take , we get that
- (i)
- (ii)
where
Corollary 11.
In Theorem 10, if we take , we get that
- (i)
- (ii)
where
3. Discussion
In this work, firstly, we began with the Introduction section, which contains a brief recall of the necessary results of the Hardy inequalities and the notions of time-scale calculus. Then, the original results are then given and proven in Section 2, since in the first theorem we established seven new inequalities that may be considered as a generalization of Theorem 4. Additionally, we obtain Inequalities (9) and (11) as a special case of our main results. After that, in the second theorem, we proved six new inequalities that may be considered as a generalization of Theorem 3.8 in [15]. In the last theorem, we investigated two main results, which generalize Theorem 3.19 in [15] After each theorem, we discussed the cases of time scales , , and .
4. Conclusions
In this manuscript, by employing the -nabla-conformable fractional calculus on the time scales of Rahmat et al. [16], several new Hardy-type inequalities were proven. The results extend several dynamic inequalities known in the literature, being new, even in the discrete and continuous settings.
Author Contributions
Conceptualization, A.A.E.-D., S.D.M., R.P.A. and J.A.; formal analysis, A.A.E.-D., S.D.M., R.P.A. and J.A.; investigation, A.A.E.-D., S.D.M., R.P.A. and J.A.; writing—original draft preparation, A.A.E.-D., S.D.M., R.P.A. and J.A.; writing—review and editing, A.A.E.-D., S.D.M., R.P.A. and J.A. All authors have read and agreed to the published version of the manuscript.
Funding
This research received no external funding.
Institutional Review Board Statement
Not applicable.
Informed Consent Statement
Not applicable.
Data Availability Statement
Not applicable.
Conflicts of Interest
The authors declare no conflict of interest.
References
- Hardy, G.H.; Littlewood, J.E.; Pólya, G. Inequalities; Cambridge University Press: Cambridge, UK, 1952. [Google Scholar]
- Řehák, P. Hardy inequality on time scales and its application to half-linear dynamic equations. J. Inequal. Appl. 2005, 2005, 942973. [Google Scholar] [CrossRef]
- Saker, S.H.; O’Regan, D. Hardy and Littlewood inequalities on time scales. Bull. Malaysian Math. Sci. Soc. 2016, 39, 527–543. [Google Scholar] [CrossRef]
- El-Deeb, A.A. Some Gronwall-bellman type inequalities on time scales for Volterra-Fredholm dynamic integral equations. J. Egypt. Math. Soc. 2018, 26, 1–17. [Google Scholar] [CrossRef]
- El-Deeb, A.A.; Xu, H.; Abdeldaim, A.; Wang, G. Some dynamic inequalities on time scales and their applications. Adv. Differ. Equ. 2019, 19, 130. [Google Scholar] [CrossRef]
- El-Deeb, A.A.; Rashid, S. On some new double dynamic inequalities associated with leibniz integral rule on time scales. Adv. Differ. Equ. 2021, 2021, 125. [Google Scholar] [CrossRef]
- Kh, F.M.; El-Deeb, A.A.; Abdeldaim, A.; Khan, Z.A. On some generalizations of dynamic Opial-type inequalities on time scales. Adv. Differ. Equ. 2019, 2019, 323. [Google Scholar] [CrossRef]
- Tian, Y.; El-Deeb, A.A.; Meng, F. Some nonlinear delay Volterra-Fredholm type dynamic integral inequalities on time scales. Discrete Dyn. Nat. Soc. 2018, 8, 5841985. [Google Scholar] [CrossRef]
- Hardy, G.H. Note on a theorem of Hilbert. Math. Z. 1920, 6, 314–317. [Google Scholar] [CrossRef]
- Hardy, G.H. Notes on some points in the integral calculus (LXIT). Messenger Math. 1928, 57, 12–16. [Google Scholar]
- Copson, E.T. Note on series of positive terms. J. Lond. Math. Soc. 1928, 1, 49–51. [Google Scholar] [CrossRef]
- Copson, E.T. Some Integral Inequalities. Proc. R. Soc. Edinb. Sect. A Math. 1976, 75, 157–164. [Google Scholar] [CrossRef]
- Bohner, M.; Peterson, A. Dynamic Equations on Time Scales: An Introduction with Applications; Springer Science and Business Media: New York, NY, USA, 2001. [Google Scholar]
- Bohner, M.; Peterson, A.C. (Eds.) Advances in Dynamic Equations on Time Scales; Springer Science and Business Media: New York, NY, USA, 2002. [Google Scholar]
- Kayar, Z.; Kaymakcalan, B. Hardy-Copson type inequalities for nabla time scale calculus. Turk. J. Math. 2021, 45, 1040–1064. [Google Scholar] [CrossRef]
- Segi Rahmat, M.; Noorani, M. A new conformable nabla derivative and its application on arbitrary time scales. Adv. Differ. Equ. 2021, 2021, 238. [Google Scholar] [CrossRef]
- Abdeljawad, T. On conformable fractional calculus. J. Comput. Appl. Math. 2015, 279, 57–66. [Google Scholar] [CrossRef]
- El-Deeb, A.A.; Awrejcewicz, J. Novel Fractional Dynamic Hardy–Hilbert-Type Inequalities on Time Scales with Applications. Mathematics 2021, 9, 2964. [Google Scholar] [CrossRef]
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