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Inequalities for convex and s-convex functions on Delta=[a,b]x[c,d] Journal of Inequalities and Applications 2012, 2012:20 doi:10.1186/1029-242X-2012-20 Muhamet Emin Ozdemir emos@atauni.

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Inequalities for convex and s-convex functions on Delta=[a,b]x[c,d]

Journal of Inequalities and Applications 2012, 2012:20 doi:10.1186/1029-242X-2012-20

Muhamet Emin Ozdemir (emos@atauni.edu.tr) Havva Kavurmaci (hkavurmaci@atauni.edu.tr) Ahmet Ocak Akdemir (ahmetakdemir@agri.edu.tr)

Merve Avci (merveavci@ymail.com)

Article type Research

Publication date 1 February 2012

Article URL http://www.journalofinequalitiesandapplications.com/content/2012/1/20

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INEQUALITIES FOR CONVEX AND

s-CONVEX FUNCTIONS ON ∆ = [a, b] × [c, d]

1 DEPARTMENT OF MATHEMATICS, K.K EDUCATION FACULTY, ATATURK

UNIVERSITY, ERZURUM 25240, TURKEY

2 DEPARTMENT OF MATHEMATICS, FACULTY OF SCIENCE AND ARTS,

A ˘ GRI ˙IBRAHIM C ¸ EC ¸ EN UNIVERSITY, A ˘ GRI 04100, TURKEY

3 DEPARTMENT OF MATHEMATICS, FACULTY OF SCIENCE AND ARTS, ADIYAMAN

UNIVERSITY, ADIYAMAN, TURKEY

∗CORRESPONDING AUTHOR: HKAVURMACI@ATAUNI.EDU.TR

EMAIL ADDRESSES:

ME: EMOS@ATAUNI.EDU.TR AO: AHMETAKDEMIR@AGRI.EDU.TR MA: M.AVCI@POSTA.ADIYAMAN.EDU.TR

Abstract In this article, two new lemmas are proved and inequalities are

established for co-ordinated convex functions and co-ordinated s-convex

func-tions.

Mathematics Subject Classification (2000): 26D10; 26D15.

Keywords: Hadamard-type inequality; co-ordinates; s-convex functions.

1

1 Introduction

Let f : I ⊆ R → R be a convex function defined on the interval I of real numbers

and a < b The following double inequality;

is well known in the literature as Hermite–Hadamard inequality Both inequalities

hold in the reversed direction if f is concave.

In [1], Orlicz defined s-convex function in the second sense as following:

Definition 1 A function f : R+→ R, where R+= [0, ∞), is said to be s-convex

in the second sense if

f (αx + βy) ≤ α s f (x) + β s f (y)

for all x, y ∈ [0, ∞), α, β ≥ 0 with α + β = 1 and for some fixed s ∈ (0, 1] We

denote by K2

s the class of all s-convex functions.

Obviously, one can see that if we choose s = 1, both definitions reduced to

ordinary concept of convexity

For several results related to above definition we refer readers to [2–10]

In [11], Dragomir defined convex functions on the co-ordinates as following:

Definition 2 Let us consider the bidimensional interval ∆ = [a, b] × [c, d] in

R2 with a < b, c < d A function f : ∆ → R will be called convex on the

co-ordinates if the partial mappings fy : [a, b] → R, fy(u) = f (u, y) and fx : [c, d] → R,

fx(v) = f (x, v) are convex where defined for all y ∈ [c, d] and x ∈ [a, b] Recall that

the mapping f : ∆ → R is convex on ∆ if the following inequality holds,

f (λx + (1 − λ)z, λy + (1 − λ)w) ≤ λf (x, y) + (1 − λ)f (z, w)

for all (x, y), (z, w) ∈ ∆ and λ ∈ [0, 1].

In [11], Dragomir established the following inequalities of Hadamard-type forco-ordinated convex functions on a rectangle from the plane R2.

Theorem 1 Suppose that f : ∆ = [a, b] × [c, d] → R is convex on the co-ordinates

on ∆ Then one has the inequalities;

The above inequalities are sharp.

Similar results can be found in [12–14]

In [13], Alomari and Darus defined co-ordinated s-convex functions and proved some inequalities based on this definition Another definition for co-ordinated s-

convex functions of second sense can be found in [15]

Definition 3 Consider the bidimensional interval ∆ = [a, b]×[c, d] in [0, ∞)2with

a < b and c < d The mapping f : ∆ → R is s-convex on ∆ if

f (λx + (1 − λ)z, λy + (1 − λ)w) ≤ λ s f (x, y) + (1 − λ) s f (z, w)

holds for all (x, y), (z, w) ∈ ∆ with λ ∈ [0, 1] and for some fixed s ∈ (0, 1].

In [16], Sarıkaya et al proved some Hadamard-type inequalities for co-ordinated

convex functions as followings:

Theorem 2 Let f : ∆ ⊂ R2 → R be a partial differentiable mapping on ∆ :=

[a, b] × [c, d] in R2 with a < b and c < d If

#

.

Theorem 3 Let f : ∆ ⊂ R2 → R be a partial differentiable mapping on ∆ :=

[a, b] × [c, d] in R2 with a < b and c < d If

¯

¯∂t∂s ∂2f

¯

¯q , q > 1, is a convex function on

the co-ordinates on ∆, then one has the inequalities:

where A, J are as in Theorem 2 and 1

where A, J are as in Theorem 2.

In [17], Barnett and Dragomir proved an Ostrowski-type inequality for doubleintegrals as following:

Theorem 5 Let f : [a, b] × [c, d] → R be continuous on [a, b] × [c, d], f 00

x,y = ∂x∂y ∂2f

exists on (a, b) × (c, d) and is bounded, that is

°

°f 00 x,y

°

∞

(1.5)

for all (x, y) ∈ [a, b] × [c, d].

In [18], Sarıkaya proved an Ostrowski-type inequality for double integrals and

gave a corollary as following:

Theorem 6 Let f : [a, b] × [c, d] → R be an absolutely continuous functions such

that the partial derivative of order 2 exist and is bounded, i.e.,

In [19], Pachpatte established a new Ostrowski type inequality similar to equality (1.5) by using elementary analysis.

in-The main purpose of this article is to establish inequalities of Hadamard-typefor co-ordinated convex functions by using Lemma 1 and to establish some new

Hadamard-type inequalities for co-ordinated s-convex functions by using Lemma 2.

2 Inequalities for co-ordinated convex functions

To prove our main result, we need the following lemma which contains kernelssimilar to Barnett and Dragomir’s kernels in [17], (see the article [17, proof ofTheorem 2.1])

Lemma 1 Let f : ∆ = [a, b] × [c, d] → R be a partial differentiable mapping on

Proof. We note that

Theorem 7 Let f : ∆ = [a, b] × [c, d] → R be a partial differentiable mapping on

By computing these integrals, we obtain

Remark 1 Suppose that all the assumptions of Theorem 7 are satisfied If we choose ∂2f

Theorem 8 Let f : ∆ = [a, b] × [c, d] → R be a partial differentiable mapping on

then the following inequality holds;





1

.

where C is in the proof of Theorem 7.

Proof. From Lemma 1, we have

Using the inequality (2.4) in (2.3), we get



1

where we have used the fact that

Remark 2 Suppose that all the assumptions of Theorem 8 are satisfied If we choose ∂t∂s ∂2f is bounded, i.e.,



1

where C is in the proof of Theorem 7.

Proof. From Lemma 1 and applying the well-known Power mean inequality for

double integrals, then one has

Computing the above integrals and using the fact that

3 Inequalities for co-ordinated s-convex functions

To prove our main results we need the following lemma:

Lemma 2 Let f : ∆ ⊂ R2→ R be an absolutely continuous function on ∆ where

a < b, c < d and t, λ ∈ [0, 1], if ∂t∂λ ∂2f ∈ L (∆), then the following equality holds:

r1+ 1

¶1

r2+ 1

¶1

r1+ 1

¶1

r2+ 1

¶1

b − a

Z b

a

f (x, c)dx

Proof. Integration by parts, we get

∂f

∂λ (tb + (1 − t) a, λd + (1 − λ) c)

¯

¯10

− r1+ 1

b − a

Z 10

− r1(r2+ 1)(b − a)(d − c)

Z 10

− (r2+ 1)(b − a)(d − c)

Z 10

f (b, λd + (1 − λ) c)dλ − (r2+ 1)

Z 10

f (a, λd + (1 − λ) c)dλ

− r2(r1+ 1)

Z 10

f (tb + (1 − t) a, d)dt − (r2+ 1)

Z 10

f (tb + (1 − t) a, c)dt (r1+ 1) (r2+ 1)

Z 10

Z 10

f (tb + (1 − t) a, λd + (1 − λ) c) dtdλ

¸

.

Using the change of the variable x = tb + (1 − t) a and y = λd + (1 − λ) c for

t, λ ∈ [0, 1] and multiplying the both sides by (r1+1)(r2+1) (b−a)(d−c) , we get the required

Theorem 11 Let f : ∆ = [a, b] × [c, d] ⊂ [0, ∞)2 → [0, ∞) be an absolutely

is s-convex function on the co-ordinates on

∆, for some fixed s ∈ (0, 1] and p > 1, then one has the inequality:

1

¶ µ

1 + r

p+1 p



1

for some fixed r1, r2∈ [0, 1] , where q = p

p−1

Proof Let p > 1 From Lemma 2 and using the H¨older inequality for double

inte-grals, we can write

|D| ≤ (b − a)(d − c)

(r1+ 1) (r2+ 1)

µZ 10

Z 10

(1) Under the assumptions of Theorem 11, if we choose r1 = r2 = 1 in (3.4),

1

¯q is s-convex function on the co-ordinates on

∆, for some fixed s ∈ (0, 1] and q ≥ 1, then one has the inequality:



1

for some fixed r1, r2∈ [0, 1]

Proof. From Lemma 2 and using the well-known Power-mean inequality, we can

write

|D| ≤ (b − a)(d − c)

(r1+ 1) (r2+ 1)

µZ 10

Z 10

By a simple computation, one can see that



1

where K, L, M , and N as in Theorem 10 By substituting these in (3.6) and

(1) Under the assumptions of Theorem 12, if we choose r1= r2= 1, we have



1

(2) Under the assumptions of Theorem 12, if we choose r1= r2= 0, we have

≤ (b − a)(d − c)

µ14



1

Remark 5 Under the assumptions of Theorem 12, if we choose r1= r2= 1 and

s = 1, we have an improvement for the inequality (1.4).

Competing interestsThe authors declare that they have no competing interests

Authors’ contributions

HK, AOA and MA carried out the design of the study and performed the analysis

MEO (adviser) participated in its design and coordination All authors read and

approved the final manuscript

[3] Dragomir, SS, Fitzpatrick, S: The Hadamard’s inequality for s-convex functions in the second

sense Demonstratio Math 32(4), 687–696 (1999)

[4] Kırmacı, US, Bakula, MK, ¨Ozdemir, ME, Peˇcari´c, J: Hadamard-type inequalities for s-convex

functions Appl Math Comput 193, 26–35 (2007)

[5] Burai, P, H´ azy, A, Juh´asz, T: Bernstein-Doetsch type results for s-convex functions Publ.

Math Debrecen 75(1–2), 23–31 (2009)

[6] Burai, P, H´ azy, A, Juh´asz, T: On approximately Breckner s-convex functions Control Cybern.

(in press)

[7] Breckner, WW: Stetigkeitsaussagen f¨ ur eine klasse verallgemeinerter konvexer funktionen in topologischen linearen r¨ aumen Publ Inst Math (Beograd) 23, 13–20 (1978)

[8] Breckner, WW, Orb´an, G: Continuity Properties of Rationally s-convex Mappings with

Val-ues in Ordered Topological Linear Space “Babes-Bolyai” University, Kolozsv´ ar (1978)

[9] Pinheiro, MR: Exploring the concept of s-convexity Aequationes Math 74(3), 201–209 (2007)

[10] Pycia, M: A direct proof of the s-H¨ older continuity of Breckner s-convex functions

Aequa-tiones Math 61, 128–130 (2001)

[11] Dragomir, SS: On Hadamard’s inequality for convex functions on the co-ordinates in a tangle from the plane Taiwanese J Math 5, 775–788 (2001)

rec-[12] Bakula, MK, Peˇcari´c, J: On the Jensen’s inequality for convex functions on the co-ordinates

in a rectangle from the plane Taiwanese J Math 5, 1271–1292 (2006)

[13] Alomari, M, Darus, M: The Hadamard’s inequality for s-convex functions of 2-variables Int.

J Math Anal 2(13), 629–638 (2008)

[14] Ozdemir, ME, Set, E, Sarıkaya, MZ: Some new Hadamard’s type inequalities for co-ordinated¨

m-convex and (α, m)-convex functions Hacettepe J Math Ist 40, 219–229 (2011)

[15] Alomari, M, Darus, M: Hadamard-type inequalities for s-convex functions Int Math Forum.