Abstract
In this paper, we derive a new extension of Hermite-Hadamard’s inequality via k-Riemann-Liouville fractional integrals. Two new k-fractional integral identities are also derived. Then, using these identities as an auxiliary result, we obtain some new k-fractional bounds which involve k-Appell’s hypergeometric functions. These bounds can be viewed as new k-fractional estimations of trapezoidal and mid-point type inequalities. These results are obtained for the functions which have the harmonic convexity property. We also discuss some special cases which can be deduced from the main results of the paper.
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1 Introduction and preliminaries
Convexity theory has played a pivotal role through its numerous applications in different fields of pure and applied sciences. In the past few years several new generalizations and extensions of classical convexity have been proposed in the literature, see [1–12]. Shi et al. [11] introduced the notion of harmonic convex sets as follows.
Definition 1.1
[11]
A set \(\Omega\subset\mathbb{R}_{+}\) is said to be a harmonically convex set if
Iscan [8] introduced the class of harmonic convex functions. The natural domain of harmonic convex functions is harmonic convex sets. Noor et al. [10] extended the definition of harmonic convex functions and defined a new generalization, which is called harmonic h-convex functions.
Definition 1.2
[10]
Let \(h:[0,1]\subseteq J\rightarrow\mathbb{R}\) be a real function. A function \(f:\Omega\subset\mathbb{R}_{+}\rightarrow\mathbb{R}\) is said to be a harmonically h-convex function if
Remark 1.3
Note that, if \(h(t)=t,t^{s},t^{-s},t^{-1}\) and \(t=1\), then the definition of harmonic h-convex functions reduces to the definitions of harmonic convex, harmonic s-convex, harmonic s-Godunova-Levin convex, harmonic Godunova-Levin and harmonic P-functions, respectively. Thus it is worth to mention here that the class of harmonic h-convex functions is quite unifying one as it naturally includes several other classes of harmonic convex functions.
Convexity theory has also a strong relationship with theory of inequalities, and resultantly many inequalities have been obtained via convex functions, see [6, 13–15]. Interested readers may find the importance of generalized convexity to variational inequalities and multiple objective optimization in [16–20]. One of the most extensively studied inequalities is Hermite-Hadamard’s inequality. This inequality was proved by Hermite and Hadamard independently. It provides a necessary and sufficient condition for a function to be convex. Dragomir et al. [6] has written a nice monograph on Hermite-Hadamard type inequalities. Interested readers may find very interesting and useful details about these inequalities in this monograph. Khattri [21] discussed some very interesting applications of Hermite-Hadamard’s inequality. Recently fractional calculus has attracted many researchers and thus become a powerful tool in many branches of mathematics. For some recent investigations in fractional calculus, see [22]. The classical form of Riemann-Liouville integrals is defined as follows.
Definition 1.4
[22]
Let \(f\in L_{1}[a,b]\). Then the Riemann-Liouville integrals \(J_{a^{+}}^{\alpha}f\) and \(J_{b^{-}}^{\alpha}f\) of order \(\alpha>0\) with \(a\geq0\) are defined by
and
where
is the well-known gamma function.
Sarikaya et al. [23] obtained Hermite-Hadamard type inequalities via Riemann-Liouville fractional integrals. Diaz et al. [24] introduced the generalized k-gamma function as
\(\Gamma_{k}\) is one parameter deformation of the classical gamma function as \(\Gamma_{k}\rightarrow\Gamma\) when \(k\rightarrow1\). \(\Gamma_{k}\) is based on the repeated appearance of the expression of
This above statement is a function of the variable ϕ and is denoted by \((\phi)_{n,k}\). It is known as Pochhammer k-symbol, which reduces to classical Pochhammer symbol \((\phi)_{n}\) by taking \(k=1\). The integral of \(\Gamma_{k}\) is given by
It is evident from (1.5) that
Diaz et al. [24] also defined a k-beta function as
The integral form of a k-beta function is given by
From (1.5) and (1.7) one can have
Using these definitions of k-gamma and k-beta functions, Mubeen et al. [25] introduced the k-Riemann-Liouville fractional integral of the type
It is obvious that when \(k\rightarrow1\), the above definition reduces to classical Riemann-Liouville fractional integrals.
Sarikaya et al. [26] introduced the notion of k-Riemann-Liouville fractional integrals and discussed some of its interesting applications with respect to inequalities.
To be more precise, let f be piecewise continuous on \(I^{*}=(0,\infty)\) and integrable on any finite subinterval of \(I=[0,\infty]\). Then, for \(t>0\), we consider the k-Riemann-Liouville fractional integral of f of order α
For more details, see [26]. Note that when \(k\rightarrow1\), k-Riemann-Liouville fractional integrals become classical Riemann-Liouville fractional integrals. It is worth mentioning here that the notion of k-Riemann-Liouville fractional integral is the significant generalization of all above Riemann-Liouville fractional integrals. We would like to emphasize that for \(k\neq1\) the properties of k-Riemann-Liouville fractional integrals are quite different from those of classical Riemann-Liouville fractional integrals. Due to these facts, the k-Riemann-Liouville fractional integrals have important applications in several branches of pure and applied sciences, see [24, 26, 27].
The integral representation of k-Appell’s series \(F_{1,k}\), where \(k>0\), is
For some more details, see [27].
2 Some new auxiliary results
In this section, we derive some new k-fractional identities which will serve as auxiliary results for the developments of our next results.
Lemma 2.1
Let \(f:I\setminus\{0\}\to\mathbb{R}\) be differentiable on \(I^{\circ}\) such that \(f'\in L[a,b]\), where \(a,b\in I\) with \(a< b\), then
where
Proof
It suffices to show that
Now integrating by parts yields
Similarly
Combining (2.1), (2.2) and (2.3) completes the proof. □
Lemma 2.2
Under the assumptions of Lemma 2.1 and \(k=1\), we have
where
This is due to Iscan [8].
Lemma 2.3
Let \(f:I\setminus\{0\}\to\mathbb{R}\) be differentiable on \(I^{\circ}\) such that \(f'\in L[a,b]\), where \(a,b\in I\) with \(a< b\), then
where
Proof
Calculate \(I_{1}\), \(I_{2}\) and \(I_{3}\) as follows:
Now
Also
Now consider
Now suppose \(u=\frac{ab}{ta+(1-t)b}\), then
Again suppose \(u=\frac{1}{t}\), then
Similarly
Using (2.7) and (2.8) in (2.6) and then adding the resultant with (2.4) and (2.5) completes the proof. □
Lemma 2.4
Under the assumptions of Lemma 2.3, if \(k\to1\), we have
where
This result is due to Set et al. [28].
3 Results and discussions
In this section, we derive some new k-fractional integral inequalities.
Theorem 3.1
Let \(f:I\setminus\{0\}\rightarrow\mathbb{R}\) be a harmonically h-convex function where \(a,b\in I\) with \(a< b\). If \(f\in L[a,b]\), then, for \(h (\frac{1}{2} )\neq0\), we have
Proof
Since f is a harmonically h-convex function, so we have
Multiplying both sides of the above inequality by \(t^{\frac{\alpha}{k}-1}\) and integrating it with respect to t on \([0,1]\), we have
This implies
Now
Adding the above two inequalities and multiplying both sides by \(t^{\frac{\alpha}{k}-1}\), we have
Integrating the above inequality with respect to t on \([0,1]\), we have
Summing inequalities (3.1) and (3.2) completes the proof. □
We now discuss some special cases of Theorem 3.1.
I. If \(h(t)=t\) in Theorem 3.1, then we have the following new result.
Corollary 3.2
Let \(f:I\setminus\{0\}\rightarrow\mathbb{R}\) be a harmonically convex function, where \(a,b\in I\) with \(a< b\). If \(f\in L[a,b]\), then we have
II. If \(h(t)=t^{s}\) in Theorem 3.1, then we have the following new result.
Corollary 3.3
Let \(f:I\setminus\{0\}\rightarrow\mathbb{R}\) be a harmonically s-convex function, where \(a,b\in I\) with \(a< b\). If \(f\in L[a,b]\), then we have
III. If \(h(t)=t^{-s}\) in Theorem 3.1, then we have the following new result.
Corollary 3.4
Let \(f:I\setminus\{0\}\rightarrow\mathbb{R}\) be a harmonically s-Godunova-Levin convex function, where \(a,b\in I\) with \(a< b\). If \(f\in L[a,b]\), then, for \(\alpha>ks\), we have
IV. If \(h(t)=1\) in Theorem 3.1, then we have the following new result.
Corollary 3.5
Let \(f:I\setminus\{0\}\rightarrow\mathbb{R}\) be a harmonic P-function, where \(a,b\in I\) with \(a< b\). If \(f\in L[a,b]\), then we have
Now using the auxiliary results, we derive some trapezoidal and mid-point type inequalities.
Theorem 3.6
Assume that \(f:[0,1]\rightarrow\mathbb{R}\) is a differentiable function such that \(\vert f^{\prime} \vert ^{q}\) is a harmonic convex function on \([0,1]\). Then
where
with
and
with
Proof
From Lemma 2.1, using the property of modulus and the power-mean inequality, we have
where
with
and using the harmonic convexity of \(\vert f^{\prime} \vert ^{q}\), we have
with
and the proof is complete. □
Theorem 3.7
Assume that \(f:[0,1]\to\mathbb{R}\) is a differentiable function such that \(\vert f^{\prime} \vert ^{q}\) is a harmonic convex function on [0,1]. Then
where I is given by (3.3) , J is given by (3.4),
and
Proof
From Lemma 2.3, using the property of modulus and the power-mean inequality, we have
where
and
and using the change of variables, we have
and
This completes the proof. □
4 Conclusion
A new refinement of Hermite-Hadamard’s inequality via k-Riemann-Liouville fractional integrals is obtained. We have derived two new k-fractional integral identities. Utilizing these identities, we have derived some new k-fractional bounds which involve k-Appell’s hypergeometric functions via the functions which have the harmonic convexity property. It is expected that the ideas and techniques of this article may be useful for future research.
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Acknowledgements
Authors are thankful to anonymous referees for their valuable comments and suggestions. Authors are pleased to acknowledge the support of Distinguished Scientist Fellowship Program (DSFP), King Saud University, Riyadh, Saudi Arabia.
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MUA, MAN, MVM and KIN worked jointly. All the authors read and approved the final manuscript.
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Awan, M.U., Noor, M.A., Mihai, M.V. et al. On bounds involving k-Appell’s hypergeometric functions. J Inequal Appl 2017, 118 (2017). https://doi.org/10.1186/s13660-017-1391-2
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DOI: https://doi.org/10.1186/s13660-017-1391-2