Journal of Inequalities in Pure and Applied Mathematics SOME INEQUALITIES OF PERTURBED TRAPEZOID TYPE ZHENG LIU Institute of Applied Mathematics Faculty of Science Anshan University of Science and Technology Anshan 114044, Liaoning, China. volume 7, issue 2, article 47, 2006. Received 21 June, 2005; accepted 16 March, 2006. Communicated by: J.E. Pečarić EMail: lewzheng@163.net Abstract Contents JJ J II I Home Page Go Back Close c 2000 Victoria University ISSN (electronic): 1443-5756 186-05 Quit Abstract A new generalized perturbed trapezoid type inequality is established by Peano kernel approach. Some related results are also given. 2000 Mathematics Subject Classification: 26D15. Key words: Perturbed trapezoid inequality; n-times continuously differentiable mapping; Absolutely continuous. Contents Some Inequalities of Perturbed Trapezoid Type Zheng Liu 1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 2 For Differentiable Mappings With Bounded Derivatives . . . . 5 3 Bounds In Terms of Some Lebesgue Norms . . . . . . . . . . . . . . 10 4 Non-Symmetric Bounds . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12 References Title Page Contents JJ J II I Go Back Close Quit Page 2 of 18 J. Ineq. Pure and Appl. Math. 7(2) Art. 47, 2006 http://jipam.vu.edu.au 1. Introduction In recent years, some authors have considered the perturbed trapezoid inequality Z b 2 (b − a) b − a 0 0 f (x) dx − [f (a) + f (b)] + [f (b) − f (a)] 2 12 a ≤ C(Γ2 − γ2 )(b − a)3 , where f : [a, b] → R is a twice differentiable mapping on (a, b) with γ2 = inf x∈[a,b] f 00 (x) > −∞ and Γ2 = supx∈[a,b] f 00 (x) < +∞ while C is a constant. √ (e.g. see [1] – [8]) It seems that the best result C = 1083 was separately and independently discovered by the authors of [5] and [8]. The perturbed trapezoid inequality has been established as (1.1) Z b (b − a)2 0 b−a 0 [f (a) + f (b)] + [f (b) − f (a)] f (x) dx − 2 12 a √ 3 ≤ (Γ2 − γ2 )(b − a)3 . 108 Some Inequalities of Perturbed Trapezoid Type Zheng Liu Title Page Contents JJ J II I Go Back Moreover, we can also find in [5] the following two perturbed trapezoid inequalities as Z b b−a (b − a)2 0 0 (1.2) f (x) dx − [f (a) + f (b)] + [f (b) − f (a)] 2 12 a 1 ≤ (Γ3 − γ3 )(b − a)4 , 384 Close Quit Page 3 of 18 J. Ineq. Pure and Appl. Math. 7(2) Art. 47, 2006 http://jipam.vu.edu.au where f : [a, b] → R is a third-order differentiable mapping on (a, b) with γ3 = inf x∈[a,b] f 000 (x) > −∞ and Γ3 = supx∈[a,b] f 000 (x) < +∞, and (1.3) Z b 2 b − a (b − a) 0 0 [f (a) + f (b)] + [f (b) − f (a)] f (x) dx − 2 12 a 1 ≤ M4 (b − a)5 , 720 where f : [a, b] → R is a fourth-order differentiable mapping on (a, b) with M4 = sup |f (4) (x)| < +∞. Some Inequalities of Perturbed Trapezoid Type x∈[a,b] The purpose of this paper is to extend these above results to a more general version by choosing appropriate harmonic polynomials such as the Peano kernel. A new generalized perturbed trapezoid type inequality is established and some related results are also given. Zheng Liu Title Page Contents JJ J II I Go Back Close Quit Page 4 of 18 J. Ineq. Pure and Appl. Math. 7(2) Art. 47, 2006 http://jipam.vu.edu.au 2. For Differentiable Mappings With Bounded Derivatives Theorem 2.1. Let f : [a, b] → R be an n-times continuously differentiable mapping, n ≥ 2 and such that Mn := supx∈[a,b] |f (n) (x)| < ∞. Then Z b (b − a)2 0 b−a [f (a) + f (b)] + [f (b) − f 0 (a)] (2.1) f (x) dx − 2 12 a ] [ n−1 2 2k+1 X a + b k(k − 1)(b − a) − f (2k) 2k−2 3(2k + 1)!2 2 k=2 √ 3 if n = 2; 3(b−a) 54 ≤ Mn × n(n−2)(b−a)nn+1 if n ≥ 3, 3(n+1)!2 where [ n−1 ] denotes the integer part of 2 n−1 . 2 Proof. It is not difficult to find the identity Z b n (2.2) (−1) Tn (x)f (n) (x) dx a Z b b−a (b − a)2 0 = f (x) dx − [f (a) + f (b)] + [f (b) − f 0 (a)] 2 12 a [ n−1 ] 2 X k(k − 1)(b − a)2k+1 (2k) a + b − f , 2k−2 3(2k + 1)!2 2 k=2 Some Inequalities of Perturbed Trapezoid Type Zheng Liu Title Page Contents JJ J II I Go Back Close Quit Page 5 of 18 J. Ineq. Pure and Appl. Math. 7(2) Art. 47, 2006 http://jipam.vu.edu.au where Tn (x) is the kernel given by (2.3) Tn (x) = (x−a)n n! − (b−a)(x−a)n−1 2(n−1)! + (b−a)2 (x−a)n−2 12(n−2)! if x ∈ a, a+b , 2 (x−b)n n! + (b−a)(x−b)n−1 2(n−1)! + (b−a)2 (x−b)n−2 12(n−2)! if x ∈ a+b ,b 2 . Using the identity (2.2), we get (2.4) Z b (b − a)2 0 b−a [f (a) + f (b)] + [f (b) − f 0 (a)] f (x) dx − 2 12 a ] [ n−1 2 2k+1 X k(k − 1)(b − a) a + b (2k) − f 3(2k + 1)!22k−2 2 k=2 Z b Z b (n) = Tn (x)f (x) dx ≤ Mn |Tn (x)| dx. a a For brevity, we put (x − a)n (b − a)(x − a)n−1 (b − a)2 (x − a)n−2 − + n! 2(n − 1)! 12(n − 2)! n−2 n(b − a)(x − a) n(n − 1)(b − a)2 (x − a) 2 = (x − a) − + , n! 2 12 a+b x ∈ a, 2 Pn (x) := Some Inequalities of Perturbed Trapezoid Type Zheng Liu Title Page Contents JJ J II I Go Back Close Quit Page 6 of 18 J. Ineq. Pure and Appl. Math. 7(2) Art. 47, 2006 http://jipam.vu.edu.au and (x − b)n (b − a)(x − b)n−1 (b − a)2 (x − b)n−2 + + Qn (x) := n! 2(n − 1)! 12(n − 2)! n−2 (x − b) n(b − a)(x − b) n(n − 1)(b − a)2 2 = (x − b) + + , n! 2 12 a+b x∈ ,b . 2 It is clear that Pn (x) and Qn (x) are symmetric with respect to the line x = a+b for n even, and symmetric with respect to the point ( a+b , 0) for n odd. 2 2 Therefore, Z b Z |Tn (x)| dx = 2 a a+b 2 |Pn (x)| dx a Z (b − a)n+1 1 n−2 2 n(n − 1) = t − nt + t dt n!2n 3 0 by substitution x = a + b−a t, 2 and it is easy to find that n(n − 1) n−2 2 rn (t) := t t − nt + 3 is always nonnegative on [0, 1] for n ≥ 3. Thus we have Z 1 Z 1 n(n − 1) n(n − 2) n−2 2 |rn (t)| dt = t t − nt + dt = 3 3(n + 1) 0 0 Some Inequalities of Perturbed Trapezoid Type Zheng Liu Title Page Contents JJ J II I Go Back Close Quit Page 7 of 18 J. Ineq. Pure and Appl. Math. 7(2) Art. 47, 2006 http://jipam.vu.edu.au for n ≥ 3, and Z 1 Z 1 2 2 t − 2t + dt |r2 (t)| dt = 3 0 0 Z 1 Z t0 2 2 2 2 = t − 2t + dt − t − 2t + dt, 3 3 0 t0 √ where t0 = 1 − 3 3 Z is the unique zero of r2 (t) in (0, 1). Hence, b |Tn (x)| dx = (2.5) a √ 3(b−a)3 , 54 n = 2, Some Inequalities of Perturbed Trapezoid Type Zheng Liu n(n−2)(b−a)n+1 , 3(n+1)!2n n ≥ 3. Consequently, the inequality (2.1) follows from (2.4) and (2.5). Remark 1. If in the inequality (2.1) we choose n = 2, 3, 4, then we get Z b √ (b − a)2 0 3 b−a 0 [f (a) + f (b)] + [f (b) − f (a)] ≤ M2 (b − a)3 , f (x) dx − 2 12 54 Za b 2 b − a (b − a) 0 0 ≤ 1 M3 (b − a)4 f (x) dx − [f (a) + f (b)] + [f (b) − f (a)] 192 2 12 a and the inequality (1.3), respectively. For convenience in further discussions, we will now collect some technical results related to (2.3) which are not difficult to obtain by elementary calculus Title Page Contents JJ J II I Go Back Close Quit Page 8 of 18 J. Ineq. Pure and Appl. Math. 7(2) Art. 47, 2006 http://jipam.vu.edu.au as: Z b Tn (x) dx = (2.6) a (2.7) max |Tn (x)| = x∈[a,b] 0, n odd, n(n−2)(b−a)n+1 , 3(n+1)!2n (b−a)2 , 12 √ n even. n = 2, 3(b−a)3 , 216 Some Inequalities of Perturbed Trapezoid Type n = 3, (n−1)(n−3)(b−a)n , 3(n!)2n Zheng Liu n ≥ 4. Title Page (2.8) Z b 1 max T2m (x) − T2m (x) dx x∈[a,b] b−a a (b−a)4 720 , = (8m3 −16m2 +2m+3)(b−a)2m , 3(2m+1)!22m Contents m = 2, m ≥ 3. JJ J II I Go Back Close Quit Page 9 of 18 J. Ineq. Pure and Appl. Math. 7(2) Art. 47, 2006 http://jipam.vu.edu.au 3. Bounds In Terms of Some Lebesgue Norms Theorem 3.1. Let f : [a, b] → R be a mapping such that the derivative f (n−1) (n ≥ 2) is absolutely continuous on [a, b]. If f (n) ∈ L∞ [a, b], then we have (3.1) Z b b−a (b − a)2 0 f (x) dx − [f (a) + f (b)] + [f (b) − f 0 (a)] 2 12 a [ n−1 ] 2 2k+1 X k(k − 1)(b − a) a + b − f (2k) 2k−2 3(2k + 1)!2 2 k=2 √3(b−a)3 , n = 2, 54 ≤ kf (n) k∞ × n(n−2)(b−a)n+1 , n ≥ 3, 3(n+1)!2n where [ n−1 ] denotes the integer part of n−1 and kf (n) k∞ := ess supx∈[a,b] |f (n) (x)| 2 2 is the usual Lebesgue norm on L∞ [a, b]. The proof of inequality (3.1) is similar to the proof of inequality (2.1) and so is omitted. Theorem 3.2. Let f : [a, b] → R be a mapping such that the derivative f (n−1) (n ≥ 2) is absolutely continuous on [a, b]. If f (n) ∈ L1 [a, b], then we have Z b (b − a)2 0 b−a [f (a) + f (b)] + [f (b) − f 0 (a)] (3.2) f (x) dx − 2 12 a Some Inequalities of Perturbed Trapezoid Type Zheng Liu Title Page Contents JJ J II I Go Back Close Quit Page 10 of 18 J. Ineq. Pure and Appl. Math. 7(2) Art. 47, 2006 http://jipam.vu.edu.au X k(k − 1)(b − a)2k+1 a + b (2k) − f 3(2k + 1)!22k−2 2 k=2 (b−a)2 , 12 √ 3(b−a)3 ≤ kf (n) k1 × , 216 (n−1)(n−3)(b−a)n [ n−1 ] 2 3(n!)2n where kf (n) k1 := Rb a n = 2, n = 3, , n ≥ 4, Some Inequalities of Perturbed Trapezoid Type |f (x)| dx is the usual Lebesgue norm on L1 [a, b]. Zheng Liu Proof. By using the identity (2.2), we get Z b (b − a)2 0 b−a [f (a) + f (b)] + [f (b) − f 0 (a)] f (x) dx − 2 12 a [ n−1 ] 2 2k+1 X k(k − 1)(b − a) a + b − f (2k) 2k−2 3(2k + 1)!2 2 k=2 Z b Z b = Tn (x)f (n) (x) dx ≤ max |Tn (x)| |f (n) (x)| dx. a Then the inequality (3.2) follows from (2.7). x∈[a,b] a Title Page Contents JJ J II I Go Back Close Quit Page 11 of 18 J. Ineq. Pure and Appl. Math. 7(2) Art. 47, 2006 http://jipam.vu.edu.au 4. Non-Symmetric Bounds Theorem 4.1. Let f : [a, b] → R be a mapping such that the derivative f (n) (n ≥ 2) is integrable with γn = inf x∈[a,b] f (n) (x) > −∞ and Γn = supx∈[a,b] f (n) (x) < +∞. Then we have (4.1) (4.2) Z b (b − a)2 0 b−a f (x) dx − [f (a) + f (b)] + [f (b) − f 0 (a)] 2 12 a ] [ n−1 2 2k+1 X k(k − 1)(b − a) a + b (2k) f − 3(2k + 1)!22k−2 2 k=2 √ 3(b−a)3 , n = 2, 54 Γn − γn ≤ × 2 n(n−2)(b−a)nn+1 , n ≥ 3 and odd, 3(n+1)!2 Z b b−a (b − a)2 0 f (x) dx − [f (a) + f (b)] + [f (b) − f 0 (a)] 2 12 a [ n−1 ] 2 2k+1 X k(k − 1)(b − a) a + b (2k) − f 2k−2 3(2k + 1)!2 2 k=2 ≤ [f (n−1) (b) − f (n−1) (a) − γn (b − a)] Some Inequalities of Perturbed Trapezoid Type Zheng Liu Title Page Contents JJ J II I Go Back Close Quit Page 12 of 18 J. Ineq. Pure and Appl. Math. 7(2) Art. 47, 2006 http://jipam.vu.edu.au × (4.3) (b−a)2 , 12 √ 3(b−a)3 , 216 (n−1)(n−3)(b−a)n , 3(n!)2n n = 2, n = 3, n ≥ 5 and odd, Z b (b − a)2 0 b−a f (x) dx − [f (a) + f (b)] + [f (b) − f 0 (a)] 2 12 a ] [ n−1 2 2k+1 X k(k − 1)(b − a) a + b (2k) f − 3(2k + 1)!22k−2 2 k=2 ≤ [Γn (b − a) − f (n−1) (b) + f (n−1) (a)] (b−a)2 , n = 2, 12 √ 3(b−a)3 × , n = 3, 216 n (n−1)(n−3)(b−a) , n ≥ 5 and odd, 3(n!)2n (4.4) Z b (b − a)2 0 b−a [f (a) + f (b)] + [f (b) − f 0 (a)] f (x) dx − 2 12 a [ n−1 ] 2 X k(k − 1)(b − a)2k+1 (2k) a + b − f 2k−2 3(2k + 1)!2 2 k=2 m(m − 1)(b − a)2m (2m−1) (2m−1) − [f (b) − f (a)] 3(2m + 1)!22m−2 Some Inequalities of Perturbed Trapezoid Type Zheng Liu Title Page Contents JJ J II I Go Back Close Quit Page 13 of 18 J. Ineq. Pure and Appl. Math. 7(2) Art. 47, 2006 http://jipam.vu.edu.au ≤ [f (2m−1) (b) − f (2m−1) (a) − γ2m (b − a)] (b−a)4 720 , × (8m3 −16m2 +2m+3)(b−a)2m 3(2m+1)!22m m = 2, , m ≥ 3, Z b (b − a)2 0 b−a (4.5) f (x) dx − [f (a) + f (b)] + [f (b) − f 0 (a)] 2 12 a n−1 [ 2 ] X k(k − 1)(b − a)2k+1 a+b (2k) f − 3(2k + 1)!22k−2 2 k=2 m(m − 1)(b − a)2m (2m−1) (2m−1) − [f (b) − f (a)] 3(2m + 1)!22m−2 (b−a)4 m = 2, 720 , ≤ [Γ2m (b−a)−f (2m−1) (b)+f (2m−1) (a)] (8m3 −16m2 +2m+3)(b−a)2m , m ≥ 3. 3(2m+1)!22m Proof. For n odd and n = 2, by (2.2) and (2.6) we get Z b n (−1) Tn (x)[f (n) (x) − C] dx a Z b (b − a)2 0 b−a = [f (a) + f (b)] + [f (b) − f 0 (a)] f (x) dx − 2 12 a [ n−1 ] 2 X k(k − 1)(b − a)2k+1 (2k) a + b − f . 2k−2 3(2k + 1)!2 2 k=2 Some Inequalities of Perturbed Trapezoid Type Zheng Liu Title Page Contents JJ J II I Go Back Close Quit Page 14 of 18 J. Ineq. Pure and Appl. Math. 7(2) Art. 47, 2006 http://jipam.vu.edu.au where C ∈ R is a constant. n If we choose C = γn +Γ , then we have 2 Z b b−a (b − a)2 0 f (x) dx − [f (a) + f (b)] + [f (b) − f 0 (a)] 2 12 a n−1 [ 2 ] X k(k − 1)(b − a)2k+1 a + b (2k) − f 3(2k + 1)!22k−2 2 k=2 Z Γn − γn b ≤ |Tn (x)| dx. 2 a and hence the inequality (4.1) follows from (2.5). If we choose C = γn , then we have Zheng Liu Title Page Z b (b − a)2 0 b−a [f (a) + f (b)] + [f (b) − f 0 (a)] f (x) dx − 2 12 a [ n−1 ] 2 2k+1 X k(k − 1)(b − a) a + b (2k) f − 3(2k + 1)!22k−2 2 k=2 Z b ≤ max |Tn (x)| |f (n) (x) − γn | dx, x∈[a,b] Some Inequalities of Perturbed Trapezoid Type Contents JJ J II I Go Back Close Quit a and hence the inequality (4.2) follows from (2.7). Similarly we can prove that the inequality (4.3) holds. Page 15 of 18 J. Ineq. Pure and Appl. Math. 7(2) Art. 47, 2006 http://jipam.vu.edu.au By (2.2) and (2.6) we can also get Z b b−a (b − a)2 0 f (x) dx − [f (a) + f (b)] + [f (b) − f 0 (a)] 2 12 a [ n−1 ] 2 X k(k − 1)(b − a)2k+1 (2k) a + b − f 3(2k + 1)!22k−2 2 k=2 m(m − 1)(b − a)2m (2m−1) (2m−1) − [f (b) − f (a)] 3(2m + 1)!22m−2 Z b Z b 1 2m = T2m (x) − T2m (x) dx [f (x) − C] dx , b−a a a where C ∈ R is a constant. If we choose C = γ2m , then we have Z b (b − a)2 0 b−a f (x) dx − [f (a) + f (b)] + [f (b) − f 0 (a)] 2 12 a [ n−1 ] 2 X k(k − 1)(b − a)2k+1 (2k) a + b − f 2k−2 3(2k + 1)!2 2 k=2 m(m − 1)(b − a)2m (2m−1) (2m−1) − [f (b) − f (a)] 3(2m + 1)!22m−2 Z b Z b 1 ≤ max T2m (x) − T2m (x) dx |f (2m) (x) − γ2m | dx x∈[a,b] b−a a a Some Inequalities of Perturbed Trapezoid Type Zheng Liu Title Page Contents JJ J II I Go Back Close Quit Page 16 of 18 J. Ineq. Pure and Appl. Math. 7(2) Art. 47, 2006 and hence the inequality (4.4) follows from (2.8). http://jipam.vu.edu.au Similarly we can prove that the inequality (4.5) holds. Remark 2. It is not difficult to find that the inequality (4.1) is sharp in the sense that we can choose f to attain R xtheR yequality in (4.1). Indeed, for n = 2, we construct the function f (x) = a a j(z) dz dy, where √ √ (3+ 3)a+(3− 3)b , Γ , a ≤ x < 2 6 √ √ √ √ 3)b (3− 3)a+(3+ 3)b j(x) = γ2 , (3+ 3)a+(3− ≤ x < , 6 6 √ √ 3)b Γ2 , (3− 3)a+(3+ ≤ x ≤ b, 6 and for n ≥ 3 and odd, we construct the function Z x Z yn Z y2 f (x) = ··· j(y1 ) dy1 · · · dyn−1 dyn , a a where j(x) = Some Inequalities of Perturbed Trapezoid Type Zheng Liu Title Page Contents a Γn , a≤x< γ , n a+b 2 a+b , 2 ≤ x ≤ b. Remark 3. If in the inequality (4.1) we choose n = 2, 3, then we recapture the inequalities (1.1) and (1.2), respectively. JJ J II I Go Back Close Quit Page 17 of 18 J. Ineq. Pure and Appl. Math. 7(2) Art. 47, 2006 http://jipam.vu.edu.au References [1] P. CERONE, On perturbed trapezoidal and midpoint rules, Korean J. Comput. Appl. Math., 2 (2002), 423–435. [2] P. CERONE AND S.S. DRAGOMIR, Trapezoidal type rules from an inequalities point of view, Handbook of Analytic-Computational Methods in Applied Mathematics, CRC Press N.Y.(2000), 65–134. [3] P. CERONE, S.S. DRAGOMIR AND J. ROUMELIOTIS, An inequality of Ostrowski-Grüss type for twice differentiable mappings and applications in numerical integration, Kyungpook Math. J., 39 (1999), 331–341. [4] X.L. CHENG, Improvement of some Ostrowski-Grüss type inequalities, Comput. Math. Appl., 42 (2001), 109–114. [5] X.L. CHENG AND J. SUN, A note on the perturbed trapezoid inequality, J. Inequal. in Pure and Appl. Math., 3(2) (2002), Art. 29. [ONLINE: http: //jipam.vu.edu.au/article.php?sid=181]. [6] S.S. DRAGOMIR, P. CERONE AND A. SOFO, Some remarks on the trapezoid rule in numerical integration, Indian J. of Pure and Appl. Math., 31(5) (2000), 489–501. [7] M. MATIĆ, J. PEČARIĆ AND N. UJEVIĆ, Improvement and further generalization of inequalities of Ostrowski-Grüss type, Computer Math. Appl., 39 (2000), 161–175. [8] N. UJEVIĆ, On perturbed mid-point and trapezoid inequalities and applications, Kyungpook Math. J., 43 (2003), 327–334. Some Inequalities of Perturbed Trapezoid Type Zheng Liu Title Page Contents JJ J II I Go Back Close Quit Page 18 of 18 J. Ineq. Pure and Appl. Math. 7(2) Art. 47, 2006 http://jipam.vu.edu.au