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Advances in Pure Mathematics** Vol.4 No.7(2014), Article
ID:48246,15
pages
DOI:10.4236/apm.2014.47044

Some Hermite-Hadamard Type Inequalities for Differentiable Co-Ordinated Convex Functions and Applications*

Kai-Chen Hsu

Department of Applied Mathematics, Aletheia University, Tamsui, New Taipei City, Taiwan

Email: victor8@mail.au.edu.tw, hsukaichen@gmail.com

Copyright © 2014 by author and Scientific Research Publishing Inc.

This work is licensed under the Creative Commons Attribution International License (CC BY).

http://creativecommons.org/licenses/by/4.0/

Received 20 May 2014; revised 18 June 2014; accepted 3 July 2014

Abstract

In this paper, we shall establish an inequality for differentiable co-ordinated convex functions on a rectangle from the plane. It is connected with the left side and right side of extended Hermite-Hadamard inequality in two variables. In addition, six other inequalities are derived from it for some refinements. Finally, this paper shows some examples that these inequalities are able to be applied to some special means.

Keywords

Hermite-Hadamard’s Inequality, Convex Function, Co-Ordintaed Convex Function, Hölder’s Inequality

1. Introduction

Throughout this paper, let be double intervals with, in, and a partial derivative of second order is denoted by for brevity.

The inequality

(1)

which holds for all convex functions is known as Hermite-Hadamard’s inequality [1] or simply Hadamard’s inequality.

For some results which generalize, improve, and extend the Inequality (1), please refer to [2] -[17] .

Based on the convex functions on, Dragomir proposed the concept of co-ordinated convex functions in [3] , defined as follows:

Definition 1. A function is said to be convex on the co-ordinates on if the partial mappings

are convex.

Definition 2. A function is said to be convex on the co-ordinates on if the inequality

(2)

holds for all and, , ,.

Clearly, we can observe that every convex function is convex on the co-ordinates, but in some special cases, some co-ordinated convex functions are not convex (please refer to [3] ). For more relevant coordinated convex functions, please refer to [5] [6] [8] -[10] [12] .

The following extended Hadamard’s inequality for co-ordinated convex functions on in two variables was proved in [3] :

Theorem 1. Suppose that is co-ordinated convex on. Then the following inequalities hold:

(3)

The above inequalities are sharp.

In [10] , Latif and Dragomir established the following Hadamard-type inequalities that gave an estimate of the difference in the left side of the Inequalities (3) for differentiable co-ordinated convex functions on.

Theorem 2. Let be a partial differentiable mapping on.

(1) If is convex on the co-ordinates on, then the following inequality holds:

(4)

(2) If is convex on the co-ordinates on and, , then the following inequality holds:

(5)

(3) If is convex on the co-ordinates on and, then the following inequality holds:

(6)

where

Remark 1. The Inequality (6) shows the result of giving the Inequality (5) an improved and simplified constant.

In [12] , Sarikaya et al. established the following results that gave an estimate of the difference in the right side of the Inequalities (3) for differentiable co-ordinated convex functions on.

Theorem 3. Let be a partial differentiable mapping on.

(1) If is convex on the co-ordinates on, then the following inequality holds:

(7)

(2) If is convex on the co-ordinates on and, , then the following inequality holds:

(8)

(3) If is convex on the co-ordinates on and, then the following inequality holds:

(9)

where

Remark 2. The Inequality (9) shows the result of giving the Inequality (8) an improved and simplified constant.

The goal of this paper is to establish an inequality which could be connected with the left side and right side of the extended Hadamard’s Inequality (3) and improve and generalize the Theorem 2 and Theorem 3. Also, the paper aims to note some consequent applications to special means.

In order to show our main results, we need the following identities (I)-(VI):

(I) For, , the following four identities hold:

(II) For, , the following four identities hold:

(III) For, , the following four identities hold:

(IV) For, , the following four identities hold:

2. Main Results

In this section, let the mapping for all be defined as follows:

(10)

In order to prove our main results, we need the following lemma:

Lemma 1. Let be a partial differentiable mapping on. Then the following inequality holds:

(11)

where

Proof. It suffices to note that

(12)

Integration by parts, we have

and

By summing the above four identities, , and and simplifying the result, it follows that

(13)

Then, multiply both sides by in (12). From (12) and (13), we get the equations and. This proof of the identity 11 is complete.

Now, we are ready to state and prove the main results.

Theorem 1. Let be defined as Lemma 1. If and the mapping is convex on the co-ordinates on then

(14)

where

and

Proof. By using the identity (11), we have

If, , it follows from the power mean inequality that

(15)

We denote and by

and

respectively, and then

(16)

By using the integration techniques, we have

and similary we get,

and

By summing the above four identities, , and and simplifying the result. Then according to (16), we get the estimated bound.

On the other hand, by using the identity mappings

and

we have

(17)

By the convexit3 of on the co-ordinates on and the Inequality (2) in, , and, then we have

and

By applying the identities (I), (II), (III) and (IV) to the above four inequalities and then simplifying the results, we get the estimated bound and the Inequality (14) for. If, then the Inequality (14) follows from (15) and (17). The proof of the Inequality (14) is complete.

Corollary 1. Under the assumptions of Theorem 1 with, , , , and, we have

(18)

where is as given in Theorem 2,

and

The Corollary 1 shows that we get the new estimated bound of the Inequality (6).

Corollary 2. Under the assumptions of Corollary 1 with, we have

(19)

where is as given in Theorem 2,

and

Remark 3. By using the convexity of on the co-ordinates on, we have the inequality

and then

Hence the Inequality (19) improves the Inequality (6).

Remark 4. Under the assumptions of Theorem 1 with, , , , , and, we get the new estimated bound and it could improve the Inequality (4).

Corollary 3. Under the assumptions of Theorem 1 with, , we have

(20)

where is as given in Theorem 3,

and

The Corollary 3 shows that we get the new estimated bound of the Inequality (9).

Corollary 4. Under the assumptions of Corollary 3 with, we have

(21)

where is as given in Theorem 3,

and

Remark 5. By using the convexity of on the co-ordinates on, we have the inequality

and then

Hence the Inequality (21) improves the Inequality (9).

Remark 6. Under the assumptions of Theorem 1 with, and, we get the new estimated bound and it could improve the Inequality (7).

Example 1. Let the function be,. Then the result of the right-hand side of (6) or (9) is, whereas the right-hand side of (19) and (21) are and, respectively.

3. Some Applications to Special Means

As in [11] we shall consider extensions of arithmetic, logarithmic and generalized logarithmic means from positive real numbers. We take

where is the set of integers.

Proposition 1. Let, , , , , , , , and, , and. Then, for, we have

(22)

Proof. The proof is immediate from Corollary 4 with, , , ,.

Proposition 2. Suppose, , , , , , ,. Then, for, we have

(23)

Proof. The result follows from Corollary 4 with

Remark 7. The Corollary 2 could also be applied to some special means.

Acknowledgements

The author is very grateful to the reviewers for carefully reading this paper and giving constructive comments.

References

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NOTES

^{*}2000 Mathematics Subject Classification. Primary 26D15. Secondary 26A51.