FRACTIONAL INTEGRAL INEQUALITIES VIA s−CONVEX FUNCTIONS 2 1 M.EMI˙NO¨ZDEMI˙RN,HAVVAKAVURMACIN,ANDC¸ETI˙NYILDIZN,⋆ 0 2 Abstract. Inthispaper,weestablishseveralinequalitiesfors−convexmap- n pingsthatareconnectedwiththeRiemann-Liouvillefractionalintegrals. Our a resultshavesomerelationshipswithcertainintegral inequalitiesinthelitera- J ture. 4 2 ] A 1. INTRODUCTION C Letf :I ⊆R→RbeaconvexfunctiondefinedontheintervalI ofrealnumbers h. and a<b. The following double inequality t a b m a+b 1 f(a)+f(b) f ≤ f(x)dx≤ 2 b−a 2 [ (cid:18) (cid:19) Za 1 is well known in the literature as Hadamard’s inequality. Both inequalities hold in v the reverseddirection if f is concave. 5 Let real function f be defined on some nonempty interval I of real line R. The 1 9 function f is said to be convex on I if inequality 4 f(tx+(1−t)y)≤tf(x)+(1−t)f(y) . 1 0 holds for all x,y ∈I and t∈[0,1]. 2 In [3], s−convex functions defined by Orlicz as following. 1 : Definition 1. A function f :R+ →R, where R+ =[0,∞), is said to be s−convex v in the first sense if i X f(αx+βy)≤αsf(x)+βsf(y) ar for all x,y ∈ [0,∞), α,β ≥ 0 with αs+βs = 1 and for some fixed s ∈ (0,1]. We denote by K1 the class of all s−convex functions. s Definition 2. A function f :R+ →R, where R+ =[0,∞), is said to be s−convex in the second sense if f(αx+βy)≤αsf(x)+βsf(y) for all x,y ∈ [0,∞), α,β ≥ 0 with α+β = 1 and for some fixed s ∈ (0,1]. We denote by K2 the class of all s−convex functions. s Date:January23,2012. 2000 Mathematics Subject Classification. 26A15,26A51,26D10. Key words and phrases. Hadamard’s Inequality, Riemann-Liouville Fractional Integration, H¨olderInequality, s−convexity. ⋆CorrespondingAuthor. 1 2 M.EMI˙NO¨ZDEMI˙RN,HAVVAKAVURMACIN,ANDC¸ETI˙NYILDIZN,⋆ Orlicz defined these class of functions in [3] and these definitions was used in the theory of Orlicz spaces in [4] and [5]. Obviously, one can see that if we choose s=1, both definitions reduced to ordinary concept of convexity. Forseveralresultsrelatedto abovedefinitions wereferreadersto[2],[6],[7]and [8]. In [6], Hadamard’s inequality which for s−convex functions in the second sence is proved by Dragomir and Fitzpatrick. Theorem 1. Suppose that f : [0,∞) → [0,∞) is an s−convex function in the second sence, where s∈(0,1) and let a,b∈[0,∞), a<b. If f ∈L ([a,b]), then the 1 following inequalities hold: b a+b 1 f(a)+f(b) (1.1) 2s−1f ≤ f(x)dx≤ . 2 b−a s+1 (cid:18) (cid:19) Z a The constant k = 1 is the best possible in the second inequality in (1.1). s+1 In [7], Kırmacı et al. obtained Hadamard type inequalities which holds for s−convex functions in the second sence. It is given in the next theorem. Theorem 2. Let f : I →R, I ⊂[0,∞), be differentiable function on I◦ such that f′ ∈ L ([a,b]), where a,b ∈ I, a < b. If |f′|q is s−convex on [a,b] for some fixed 1 s∈(0,1) and q ≥1, then: (1.2) f(a)+f(b) − 1 b f(x)dx ≤ b−a 1 q−q1 s+ 21 s q1 |f′(a)|q+|f′(b)|q q1 . (cid:12) 2 b−a (cid:12) 2 2 (s+1)(s+2) (cid:12)(cid:12) Za (cid:12)(cid:12) (cid:18) (cid:19) " (cid:0) (cid:1) # (cid:2) (cid:3) (cid:12) (cid:12) (cid:12) In [1], Dragomir and Agarw(cid:12)alproved the following inequality. (cid:12) (cid:12) Theorem 3. Let f : I◦ ⊆ R → R be a differentiable mapping on I◦,a,b ∈ I◦ with a < b, and let p > 1. If the new mapping |f′|p−p1 is convex on [a,b], then the £ollowing inequality holds: f(a)+f(b) 1 b b−a |f′(a)|p−p1 +|f′(b)|p−p1 p−p1 (1.3) − f(x)dx ≤ . (cid:12)(cid:12) 2 b−aZ (cid:12)(cid:12) 2(p+1)p1 " 2 # (cid:12) a (cid:12) In [1(cid:12)(cid:12)2], Set et al. proved the follo(cid:12)(cid:12)wing Hadamard type inequality for s−convex (cid:12) (cid:12) functions in the second sense via Riemann-Liouville fractional integral. Theorem 4. Let f :[a,b]⊂[0,∞)→R be a differentiable mapping on (a,b) with a < b such that f′ ∈ L[a,b]. If |f′|q is s−convex in the second sense on [a,b] for some fixed s∈(0,1] and q ≥1, then the following inequality for fractional integrals holds (1.4) f(a)+f(b) Γ(α+1) − [Jα f(b)+Jα f(a)] 2 2(b−a)α a+ b− (cid:12) (cid:12) (cid:12)(cid:12)b−a 2 1 1−q1 (cid:12)(cid:12) ≤ (cid:12) 1− (cid:12) 2 α+1 2α (cid:20) (cid:18) (cid:19)(cid:21) 1 1 2α+s−1 q1 ′ q ′ q 1 × β ,s+1,α+1 −β ,α+1,s+1 + |f (a)| +|f (b)| q . 2 2 (α+s+1)2α+s (cid:20) (cid:18) (cid:19) (cid:18) (cid:19) (cid:21) (cid:0) (cid:1) FRACTIONAL INEQUALITIES 3 Now,wegivesomenecessarydefinitions andmathematicalpreliminariesoffrac- tional calculus theory which are used throughout this paper, see([9]). Definition 3. Let f ∈L [a,b]. The Riemann-Liouville integrals Jα f and Jα f of 1 a+ b− order α>0 with a≥0 are defined by x Jα f(x)= 1 (x−t)α−1f(t)dt, x>a a+ Γ(α) Z a and b Jα f(x)= 1 (t−x)α−1f(t)dt, x<b b− Γ(α) Z x ∞ respectively where Γ(α)= e−uuα−1du. Here is J0 f(x)=J0 f(x)=f(x). a+ b− 0 R In the case of α=1, the fractionalintegralreduces to the classicalintegral. For some recent results connected with fractional integral inequalities see ([10]-[17]). In order to prove our main theorems, we need the following lemma: Lemma 1. (see [18]) Let f : I ⊂ R → R be a differentiable mapping on I with a < r, a,r ∈ I. If f′ ∈ L[a,r], then the following equality for fractional integral holds: f(a)+f(r) Γ(α+1) − [Jα f(r)+Jα f(a)] 2 2(r−a)α a+ r− r−a 1 = [(1−t)α−tα]f′(r+(a−r)t)dt. 2 Z0 2. MAIN RESULTS Theorem 5. Let f : [a,b] ⊂ [0,∞) → R be a differentiable mapping on (a,b) with a < r ≤ b such that f′ ∈ L[a,b]. If |f′| is s−convex on [a,b] for some fixed s∈(0,1], then the following inequality for fractional integrals holds f(a)+f(r) Γ(α+1) − [Jα f(r)+Jα f(a)] 2 2(r−a)α a+ r− (cid:12) (cid:12) (cid:12)r−a 1 1 (cid:12) 2α+s−1 (cid:12) (cid:12) ′ ′ ≤ (cid:12) β ,s+1,α+1 −β ,α+1,s+(cid:12)1 + [|f (a)|+|f (r)|]. 2 2 2 (α+s+1)2α+s (cid:20) (cid:18) (cid:19) (cid:18) (cid:19) (cid:21) Proof. From Lemma 1 and using the properties of modulus, we get f(a)+f(r) Γ(α+1) − [Jα f(r)+Jα f(a)] 2 2(r−a)α a+ r− (cid:12) (cid:12) ≤ (cid:12)(cid:12)(cid:12)r−a 1|(1−t)α−tα||f′(r+(a−r)t)|dt. (cid:12)(cid:12)(cid:12) 2 Z0 Since |f′| is s−convex on [a,b], we obtain inequality |f′(r+(a−r)t)| =|f′(ta+(1−t)r)|≤ts|f′(a)|+(1−t)s|f′(r)|, t∈(0,1). 4 M.EMI˙NO¨ZDEMI˙RN,HAVVAKAVURMACIN,ANDC¸ETI˙NYILDIZN,⋆ Hence, f(a)+f(r) Γ(α+1) − [Jα f(r)+Jα f(a)] 2 2(r−a)α a+ r− (cid:12) (cid:12) (cid:12) 1 (cid:12) ≤ (cid:12)(cid:12)r−a 2 [(1−t)α−tα][ts|f′(a)|+(1−t)s(cid:12)(cid:12)|f′(r)|]dt 2 (Z0 1 + [tα−(1−t)α][ts|f′(a)|+(1−t)s|f′(r)|]dt 1 ) Z2 and 21 1 1 ts(1−t)αdt = (1−t)stαdt=β ;s+1,α+1 , Z0 Z21 (cid:18)2 (cid:19) 12 1 1 (1−t)stαdt = ts(1−t)αdt=β ;α+1,s+1 , Z0 Z21 (cid:18)2 (cid:19) 12 1 1 ts+αdt = (1−t)s+αdt= , Z0 Z21 2s+α+1(s+α+1) 12 1 1 1 (1−t)s+αdt= ts+αdt= − . Z0 Z12 s+α+1 2s+α+1(s+α+1) We obtain f(a)+f(r) Γ(α+1) − [Jα f(r)+Jα f(a)] 2 2(r−a)α a+ r− (cid:12) (cid:12) (cid:12)r−a 1 1 (cid:12) 2α+s−1 (cid:12) (cid:12) ′ ′ ≤ (cid:12) β ,s+1,α+1 −β ,α+1,s+(cid:12)1 + [|f (a)|+|f (r)|]. 2 2 2 (α+s+1)2α+s (cid:20) (cid:18) (cid:19) (cid:18) (cid:19) (cid:21) (cid:3) Theorem 6. Let f :[a,b]⊂[0,∞)→R be a differentiable mapping on (a,b) with a < r ≤ b such that f′ ∈ L[a,b]. If |f′|q is s−convex in the second sense on [a,b] for some fixed s∈(0,1] and q >1 with 1 + 1 =1, then the following inequality for p q fractional integrals holds f(a)+f(r) Γ(α+1) − [Jα f(r)+Jα f(a)] 2 2(r−a)α a+ r− (cid:12) (cid:12) (cid:12)(cid:12)r−a 1 p1 |f′(a)|q+|f′(r)|q q1 (cid:12)(cid:12) ≤ (cid:12) (cid:12) 2 αp+1 s+1 (cid:18) (cid:19) (cid:18) (cid:19) where α∈[0,1]. FRACTIONAL INEQUALITIES 5 Proof. By Lemma 1 and using Ho¨lder inequality with the properties of modulus, we have f(a)+f(r) Γ(α+1) − [Jα f(r)+Jα f(a)] 2 2(r−a)α a+ r− (cid:12) (cid:12) ≤ (cid:12)(cid:12)(cid:12)r−a 1|(1−t)α−tα||f′(r+(a−r)t)|dt (cid:12)(cid:12)(cid:12) 2 Z0 1 1 1 p 1 q r−a ≤ |(1−t)α−tα|pdt |f′(r+(a−r)t)|qdt . 2 Z Z 0 0 We know that for α∈[0,1] and ∀t ,t ∈[0,1], 1 2 |tα−tα|≤|t −t |α, 1 2 1 2 therefore 1 1 |(1−t)α−tα|pdt ≤ |1−2t|αpdt Z Z 0 0 12 1 = [1−2t]αpdt+ [2t−1]αpdt Z Z 0 1 2 1 = . αp+1 Since |f′|q is s−convex on [a,b],we get f(a)+f(r) Γ(α+1) − [Jα f(r)+Jα f(a)] 2 2(r−a)α a+ r− (cid:12) (cid:12) (cid:12) (cid:12) 1 (cid:12) 1 1 (cid:12) q ≤ (cid:12)r−a 1 p ts|f′(a)|q+(1−t)s|f(cid:12)′(r)|q dt 2 αp+1 (cid:18) (cid:19) Z 0 (cid:2) (cid:3) r−a 1 p1 |f′(a)|q+|f′(r)|q q1 = 2 αp+1 s+1 (cid:18) (cid:19) (cid:18) (cid:19) which completes the proof. (cid:3) Corollary 1. If in Theorem 6, we choose r =b then, we have f(a)+f(b) Γ(α+1) (2.1) − [Jα f(b)+Jα f(a)] 2 2(b−a)α a+ b− (cid:12) (cid:12) (cid:12)(cid:12)b−a 1 p1 |f′(a)|q+|f′(b)|q q1 (cid:12)(cid:12) ≤ (cid:12) . (cid:12) 2 αp+1 s+1 (cid:18) (cid:19) (cid:18) (cid:19) Remark 1. If we choose α=1 ve s=1 in Corollary 6 then, we have f(a)+f(b) 1 b b−a |f′(a)|q+|f′(b)|q 1q − f(x)dx ≤ (cid:12)(cid:12)(cid:12) 2 b−aZa (cid:12)(cid:12)(cid:12) 2(p+1)p1 (cid:20) 2 (cid:21) (cid:12) (cid:12) which is(cid:12)the inequality in (1.3). (cid:12) (cid:12) (cid:12) 6 M.EMI˙NO¨ZDEMI˙RN,HAVVAKAVURMACIN,ANDC¸ETI˙NYILDIZN,⋆ Theorem 7. Let f :[a,b]⊂[0,∞)→R be a differentiable mapping on (a,b) with a<r ≤b such that f′ ∈L[a,b]. If |f′|q is s−convex in the second sense on [a,b] for some fixed s∈(0,1] and q ≥1, then the following inequality for fractional integrals holds f(a)+f(r) Γ(α+1) − [Jα f(r)+Jα f(a)] 2 2(r−a)α a+ r− (cid:12) (cid:12) (cid:12)(cid:12)r−a 2 1 1−1q (cid:12)(cid:12) ≤ (cid:12) 1− (cid:12) 2 α+1 2α (cid:20) (cid:18) (cid:19)(cid:21) 1 1 2α+s−1 q1 ′ q ′ q 1 × β ,s+1,α+1 −β ,α+1,s+1 + |f (a)| +|f (r)| q . 2 2 (α+s+1)2α+s (cid:20) (cid:18) (cid:19) (cid:18) (cid:19) (cid:21) (cid:0) (cid:1) Proof. From Lemma 1 and using the well-known power mean inequality with the properties of modulus, we have f(a)+f(r) Γ(α+1) − [Jα f(r)+Jα f(a)] 2 2(r−a)α a+ r− (cid:12) (cid:12) ≤ (cid:12)(cid:12)(cid:12)r−a 1|(1−t)α−tα||f′(r+(a−r)t)|dt (cid:12)(cid:12)(cid:12) 2 Z0 1 1−1q 1 1q r−a ≤ |(1−t)α−tα|dt |(1−t)α−tα||f′(r+(a−r)t)|qdt 2 Z Z 0 0 On the other hand, we have 1 1 1 2 |(1−t)α−tα|dt = [(1−t)α−tα]dt+ [tα−(1−t)α]dt Z0 Z0 Z12 2 1 = 1− . α+1 2α (cid:18) (cid:19) Since |f′|q is s−convex on [a,b], we obtain |f′(r+(a−r)t)|q =|f′(ta+(1−t)r)|q ≤ts|f′(a)|q +(1−t)s|f′(r)|q, t∈(0,1) and 1 1 |(1−t)α−tα||f′(r+(a−r)t)|qdt ≤ |(1−t)α−tα| ts|f′(a)|q+(1−t)s|f′(r)|q dt Z0 Z0 1 (cid:2) (cid:3) = 2 [(1−t)α−tα] ts|f′(a)|q+(1−t)s|f′(r)|q dt Z0 1 (cid:2) (cid:3) + [tα−(1−t)α] ts|f′(a)|q +(1−t)s|f′(r)|q dt 1 Z2 (cid:2) (cid:3) FRACTIONAL INEQUALITIES 7 Since 12 1 1 ts(1−t)αdt = (1−t)stαdt=β ;s+1,α+1 , Z0 Z21 (cid:18)2 (cid:19) 12 1 1 (1−t)stαdt = ts(1−t)αdt=β ;α+1,s+1 , Z0 Z21 (cid:18)2 (cid:19) 12 1 1 ts+αdt = (1−t)s+αdt= Z0 Z21 2s+α+1(s+α+1) and 21 1 1 1 (1−t)s+αdt= ts+αdt= − . Z0 Z12 s+α+1 2s+α+1(s+α+1) Therefore, we have f(a)+f(r) Γ(α+1) − [Jα f(r)+Jα f(a)] 2 2(r−a)α a+ r− (cid:12) (cid:12) (cid:12)(cid:12)r−a 2 1 1−1q (cid:12)(cid:12) ≤ (cid:12) 1− (cid:12) 2 α+1 2α (cid:20) (cid:18) (cid:19)(cid:21) 1 1 2α+s−1 ′ q ′ q q1 × β ,s+1,α+1 −β ,α+1,s+1 − |f (a)| +|f (r)| . 2 2 (α+s+1)2α+s (cid:26)(cid:20) (cid:18) (cid:19) (cid:18) (cid:19) (cid:21) (cid:27) (cid:0) (cid:1) (cid:3) Remark 2. If we choose r =b in Theorem 7, we obtain the inequality in (1.4) of Theorem 4. Remark 3. If we choose r =b and α= 1 in Theorem 7, we obtain the inequality in (1.2) of Theorem 2. Theorem 8. Let f :[a,b]⊂[0,∞)→R be a differentiable mapping on (a,b) with a < r ≤ b such that f′ ∈ L[a,b]. If |f′|q is s−concave on [a,b] and q > 1 with 1 + 1 =1, then the following inequality for fractional integrals holds p q f(a)+f(r) Γ(α+1) − [Jα f(r)+Jα f(a)] 2 2(r−a)α a+ r− (cid:12) (cid:12) (cid:12) 1 (cid:12) ≤ (cid:12)(cid:12)r−a 1 p f′ a+r . (cid:12)(cid:12) 22−qs (cid:18)αp+1(cid:19) (cid:12) (cid:18) 2 (cid:19)(cid:12) (cid:12) (cid:12) Proof. From Lemma 1 and using Ho¨lde(cid:12)r inequality,(cid:12)we have (cid:12) (cid:12) f(a)+f(r) Γ(α+1) − [Jα f(r)+Jα f(a)] 2 2(r−a)α a+ r− (cid:12) (cid:12) ≤ (cid:12)(cid:12)(cid:12)r−a 1|(1−t)α−tα||f′(r+(a−r)t)|dt (cid:12)(cid:12)(cid:12) 2 Z0 1 1 1 p 1 q ≤ r−a |(1−t)α−tα|pdt |f′(r+(a−r)t)|qdt . 2 Z Z 0 0 8 M.EMI˙NO¨ZDEMI˙RN,HAVVAKAVURMACIN,ANDC¸ETI˙NYILDIZN,⋆ Since |f′|q is s−concave on [a,b],we get 1 a+r q |f′(r+(a−r)t)|qdt≤2s−1 f′ , 2 Z (cid:12) (cid:18) (cid:19)(cid:12) 0 (cid:12) (cid:12) so (cid:12) (cid:12) (cid:12) (cid:12) f(a)+f(r) Γ(α+1) − [Jα f(r)+Jα f(a)] 2 2(r−a)α a+ r− (cid:12) (cid:12) (cid:12) 1 (cid:12) ≤ (cid:12)(cid:12)r−a 1 p f′ a+r . (cid:12)(cid:12) 22−qs (cid:18)αp+1(cid:19) (cid:12) (cid:18) 2 (cid:19)(cid:12) which completes the proof. (cid:12)(cid:12) (cid:12)(cid:12) (cid:3) (cid:12) (cid:12) Corollary 2. 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[18] M.E.O¨zdemir,S.S.DragomirandC¸.Yıldız,TheHadamard’s inequalityforconvexfunction viafractional integrals, Submitted. NATATU¨RKUNIVERSITY,K.K.EDUCATIONFACULTY, DEPARTMENTOFMATH- EMATICS,25240,CAMPUS,ERZURUM, TURKEY E-mail address: [email protected] E-mail address: [email protected] E-mail address: [email protected]