Research Article | Open Access
Estimates of Upper Bound for a Function Associated with Riemann-Liouville Fractional Integral via -Convex Functions
A new identity involving Riemann-Liouville fractional integral is proposed. The result is then used to obtain some estimates of upper bound for a function associated with Riemann-Liouville fractional integral via -convex functions. An application for establishing the inequalities related to special means is also considered.
A set is said to be convex, if
A function is said to be convex, if
In 1978, Breckner  introduced the concept of -convex functions as a generalization of convex functions, as follows.
Definition 1 (see ). Let be a real number, . A function is said to be -convex, if
In recent years several new extensions of classical convexity have been proposed in the literature. Varošanec  investigated a more generalized class of convex functions named -convex function, as follows.
Definition 2 (see ). Let be a nonnegative function. A function is said to be -convex, if
It has been observed that the class of -convex functions unifies several other classes of convexity; for example, if we take , , , and , respectively, then we have the class of -convex functions , the class of -functions , the class of -Godunova-Levin type functions , and the class of -functions . For more details on convexity and its generalizations, see [6–9].
Convexity of a function plays a vital role in theory of inequalities, because many inequalities can easily be obtained using the functions having convexity properties. Hermite and Hadamard’s result which is known as Hermite-Hadamard’s inequality is one of the most fascinating results in the field of integral inequalities. This inequality provides a lower and an upper estimate for the integral average of any convex function defined on an interval. This famous result reads as follows.
Let be a convex function, then
Sarikaya et al.  gave a generalization of Hermite-Hadamard’s inequality using the -convexity of the function as follows.
Let be -convex function, then, for , we have
Although the fractional calculus has a long history, it plays significant role in different fields of pure and applied mathematics . Up to now, the study of the fractional calculus is still very active. Sarikaya et al.  used the concepts of Riemann-Liouville integrals to obtain the fractional version of Hermite-Hadamard’s inequality. In fact, there are numerous new inequalities that have been obtained using the techniques of fractional calculus. For more details, see [12–15].
In this paper, we present a new integral identity for differentiable functions involving fractional integrals. Then using this auxiliary result we establish our main results that are the estimates of upper bound for a function associated with Riemann-Liouville fractional integral via -convex functions. At the end of the paper, we give an application of the obtained results to the special means.
We begin with recalling the definition of Riemann-Liouville fractional integrals, as follows.
Definition 3 (see ). Let . The Riemann-Liouville integrals and of order with are defined by andwhere is the Gamma function.
The integral form of the hypergeometric function is where is the Beta function.
2. Main Results
In this section, we consider the estimates of upper bound for the function below, which is associated with Riemann-Liouville fractional integral. Consider the following:
In order to establish the estimates of upper bound for , we first prove an auxiliary result which plays an important role in dealing with subsequent results.
Lemma 4. Let be differentiable function on with . If , , and , then
Based on Lemma 4, we are now in a position to establish our main results.
Theorem 5. Let be differentiable function on with . If , , and and is -convex function, then where
We now discuss some special cases which can be deduced directly from Theorem 5.
(I) Putting in Theorem 5, we have the following.
Corollary 6. Let be differentiable function on with . If , , and and is convex function, then
(II) Putting in Theorem 5, we have the following.
Corollary 7. Let be differentiable function on with . If , , and and is -convex function, then
(III) Taking in Theorem 5, we have the following.
Corollary 8. Let be differentiable function on with . If , , and and is -function, then
(IV) Taking in Theorem 5, we have the following.
Corollary 9. Let be differentiable function on with . If , , and and is -Godunova-Levin type function, then
Theorem 10. Let be differentiable function on with , , , and , and let be -convex function, . Then
We give now four corollaries that follow from the special cases of Theorem 10.
(I) Choosing in Theorem 10, we have the following.
Corollary 11. Let be differentiable function on with , , , and , and let be convex function, . Then
(II) Choosing in Theorem 10, we have the following.
Corollary 12. Let be differentiable function on with , , , and , and let be -convex function, . Then
(III) Putting in Theorem 10, we have the following.
Corollary 13. Let be differentiable function on with , , , and , and let be -function, . Then
(IV) Putting in Theorem 10, we have the following.
Corollary 14. Let be differentiable function on with , , , and , and let be -Godunova-Levin type function, . Then
3. Application to Special Means
In this section, we give an application of the obtained results to special means.
Definition 15 (see ). Recall the following definitions.(1) For arbitrary positive numbers (, is called the logarithmic mean.(2) For arbitrary real numbers , is called the arithmetic mean.(3) The extended logarithmic mean of two positive numbers is defined by
We focus on the estimation of upper bound for the difference between logarithmic mean and arithmetic mean; we shall establish two inequalities related to these means.
Proposition 16. If , , then where
Proof. We start by verifying that is -convex on .
In view of which implies that is convex on , thus for all , , and we have Hence, is -convex on
Now, putting , , , in Corollary 7, we obtainandNote that the function is -convex on . Hence, the inequality (32) follows straightway from the inequality given in Corollary 7.
Proposition 17. If , , , , and , thenwhere
Proof. Taking , , in Corollary 12, we obtainand It remains to prove that is -convex on .
In fact, one has It follows that is convex on ; thus for all , , and we have which implies that is -convex on .
Now, utilizing the fact that is -convex on , we can deduce the desired inequality (38) from Corollary 12.
The datasets used or analysed during the current study are available from the corresponding author upon reasonable request.
Conflicts of Interest
The authors declare that they have no competing interests.
All authors read and approved the final manuscript.
The work of the first author was supported by the Natural Science Foundation of Fujian Province of China (Grant no. 2016J01023) and the Teaching Reform Project of Longyan University (Grant no. 2017JZ02).
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Copyright © 2019 Shan-He Wu and Muhammad Uzair Awan. 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.