Journal of Inequalities in Pure and Applied Mathematics HILBERT–PACHPATTE TYPE MULTIDIMENSIONAL INTEGRAL INEQUALITIES volume 5, issue 2, article 34, 2004. G.D. HANDLEY, J.J. KOLIHA AND J. PEČARIĆ Department of Mathematics and Statistics University of Melbourne Melbourne, VIC 3010 Australia. EMail: g.handley@pgrad.unimelb.edu.au EMail: j.koliha@ms.unimelb.edu.au Faculty of Textile Engineering University of Zagreb 10 000 Zagreb Croatia. EMail: pecaric@juda.element.hr Received 24 September, 2003; accepted 01 March, 2004. Communicated by: S.S. Dragomir Abstract Contents JJ J II I Home Page Go Back Close c 2000 Victoria University ISSN (electronic): 1443-5756 129-03 Quit Abstract In this paper we use a new approach to obtain a class of multivariable integral inequalities of Hilbert type from which we can recover as special cases integral inequalities obtained recently by Pachpatte and the present authors. 2000 Mathematics Subject Classification: 26D15 Key words: Hilbert’s inequality, Hilbert-Pachpatte integral inequalities, Hölder’s inequality. Contents 1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 2 Notation and Preliminaries . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 3 The Main Result . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 4 Applications to Derivatives . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11 References Hilbert–Pachpatte Type Multidimensional Integral Inequalities G.D. Handley, J.J. Koliha and J. Pečarić Title Page Contents JJ J II I Go Back Close Quit Page 2 of 18 J. Ineq. Pure and Appl. Math. 5(2) Art. 34, 2004 http://jipam.vu.edu.au 1. Introduction The integral version of Hilbert’s inequality [7, Theorem 316] has been generalized in several directions (see [1, 3, 4, 7, 8, 9, 20, 21, 22]). Recently, inequalities similar to those of Hilbert were considered by Pachpatte in [12, 13, 14, 15, 16, 19]. The present authors in [5, 6] established a new class of related inequalities, which were further extended by Dragomir and Kim [2]. Two and higher dimensional variants were treated by Pachpatte in [17, 18]. In the present paper we use a new systematic approach to these inequalities based on Theorem 3.1, which serves as an abstract springboard to classes of concrete inequalities. To motivate our investigation, we give a typical result of [17]. In this theorem, H(I × J) denotes the class of functions u ∈ C (n−1,m−1) (I × J) such that D1i u(0, t) = 0, 0 ≤ i ≤ n − 1, t ∈ J, D2j u(s, 0) = 0, 0 ≤ j ≤ m − 1, s ∈ I, and D1n D2m−1 u(s, t) and D1n−1 D2m u(s, t) are absolutely continuous on I × J. Here I, J are intervals of the type Iξ = [0, ξ) for some real ξ > 0. Theorem 1.1 (Pachpatte [17, Theorem 1]). Let u(s, t) ∈ H(Ix × Iy ) and v(k, r) ∈ H(Iz × Iw ). Then, for 0 ≤ i ≤ n − 1, 0 ≤ j ≤ m − 1, the following inequality holds: ! Z xZ y Z zZ w |D1i D2j u(s, t) D1i D2j v(k, r)| dk dr ds dt 2n−2i−1 t2m−2j−1 + k 2n−2i−1 r 2m−2j−1 0 0 0 0 s Z x Z y 21 1 2√ n m 2 (x − s)(y − t)|D1 D2 u(s, t)| ds dt ≤ [Ai,j Bi,j ] xyzw 2 0 0 Z z Z w 21 n m 2 × (z − k)(w − r)|D1 D2 v(k, r)| dk dr , 0 Hilbert–Pachpatte Type Multidimensional Integral Inequalities G.D. Handley, J.J. Koliha and J. Pečarić Title Page Contents JJ J II I Go Back Close Quit Page 3 of 18 0 J. Ineq. Pure and Appl. Math. 5(2) Art. 34, 2004 http://jipam.vu.edu.au where Aij = 1 , (n − i − 1)!(m − j − 1)! Bij = 1 . (2n − 2i − 1)(2m − 2j − 1) The purpose of the present paper is to obtain a simultaneous generalization of Pachpatte’s multivariable results [17], and of the results [5, 6] of the present authors. The single variable results [14, 15, 16, 19] follow as special cases of our theorems. Our treatment is based on Theorem 3.1, in particular on the abstract inequality (3.1), which yields a variety of special cases when the functions Φi are specified. Hilbert–Pachpatte Type Multidimensional Integral Inequalities G.D. Handley, J.J. Koliha and J. Pečarić Title Page Contents JJ J II I Go Back Close Quit Page 4 of 18 J. Ineq. Pure and Appl. Math. 5(2) Art. 34, 2004 http://jipam.vu.edu.au 2. Notation and Preliminaries By Z (Z+ ) and R (R+ ) we denote the sets of all (nonnegative) integers and (nonnegative) real numbers. We will be working with functions of d variables, where d is a fixed positive integer, writing the variable as a vector s = (s1 , . . . , sd ) ∈ Rd . A multiindex m is an element m = (m1 , . . . , md ) of Zd+ . As usual, the factorial of a multiindex m is defined by m! = m1 ! · · · md !. An integer j may be regarded as the multiindex (j, . . . , j) depending on the context. For vectors in Rd and multiindices we use the usual operations of vector addition and multiplication of vectors by scalars. We write s ≤ τ (s < τ ) if sj ≤ τ j (sj < τ j ) for 1 ≤ j ≤ d. The same convention will apply to multiindices. In particular, s ≥ 0 (s > 0) will mean sj ≥ 0 (sj > 0) for 1 ≤ j ≤ d. If s = (s1 , . . . , sd ) ∈ Rd and s > 0, we define the cell Q(s) = [0, s1 ] × · · · × [0, sj ] × · · · × [0, sd ]; replacing the factor [0, sj ] by {0} in this product, we get the face ∂j Q(s) of Q(s). Let s = (s1 , . . . , sd ), τ = (τ 1 , . . . , τ d ) ∈ Rd , s, τ > 0, let k = (k 1 , . . . , k d ) be a multiindex and let and u : Q(s) → R. Write Dj = ∂s∂ j . We use the following notation: τ1 τd sτ = (s1 ) · · · (sd ) , k1 kd Dk u(s) = D1 · · · Dd u(s), Z s Z s1 Z sd u(τ ) dτ = ··· u(τ ) dτ 1 · · · dτ d . 0 0 0 Hilbert–Pachpatte Type Multidimensional Integral Inequalities G.D. Handley, J.J. Koliha and J. Pečarić Title Page Contents JJ J II I Go Back Close Quit Page 5 of 18 J. Ineq. Pure and Appl. Math. 5(2) Art. 34, 2004 http://jipam.vu.edu.au An exponent α ∈ R in the expression sα , where s ∈ Rd , will be regarded as a multiexponent, that is, sα = s(α,...,α) . Another positive integer n will be fixed throughout. The following notation and hypotheses will be used throughout the paper: I = {1, . . . , n} n∈N mi , i ∈ I mi = (m1i , . . . mdi ) ∈ Zd+ xi , i ∈ I xi = (x1i , . . . , xdi ) ∈ Rd , xi > 0 pi , qi , i ∈ I pi , qi ∈ R+ , p1i + q1i = 1 P P 1 = ni=1 p1i , 1q = ni=1 q1i p p, q ai , b i , i ∈ I wi , i ∈ I ai , bi ∈ R+ , ai + bi = 1 P wi ∈ R, wi > 0, ni=1 wi = 1. Throughout the paper, ui , vi , Φ will denote functions from [0, xi ] to R of sufficient smoothness. If m is a multiindex and x ∈ Rd , x > 0, then C m [0, x] will denote the set of all functions u : [0, x] → R which possess continuous derivatives Dk u, where 0 ≤ k ≤ m. The coefficients pi , qi are conjugate Hölder exponents used in applications of Hölder’s inequality, and the coefficients ai , bi are used in exponents to factorize integrands. The coefficients wi act as weights in applications of the geometricarithmetic mean inequality; this enables us to pass from products to sums of terms. Hilbert–Pachpatte Type Multidimensional Integral Inequalities G.D. Handley, J.J. Koliha and J. Pečarić Title Page Contents JJ J II I Go Back Close Quit Page 6 of 18 J. Ineq. Pure and Appl. Math. 5(2) Art. 34, 2004 http://jipam.vu.edu.au 3. The Main Result First we present a theorem that can be regarded as a template for concrete inequalities obtained by selecting suitable functions Φi in (3.1). A special case of this theorem is given in [6, Theorem 3.1]. Theorem 3.1. Let vi , Φi ∈ C(Q(xi )) and let ci be multiindices for i ∈ I. If Z si (3.1) |vi (si )| ≤ (si − τi )ci Φi (τi ) dτi , si ∈ Q(xi ), i ∈ I, Hilbert–Pachpatte Type Multidimensional Integral Inequalities 0 then Z x1 Z ... (3.2) 0 0 Qn xn i=1 |vi (si )| ds1 · · · dsn (α +1)/(qi wi ) wi si i p1 n n Z xi Y Y i 1/qi , ≤U xi (xi − si )βi +1 Φi (si )pi dsi G.D. Handley, J.J. Koliha and J. Pečarić Pn i=1 i=1 0 i=1 i=1 [(αi 1 + 1)1/qi (βi Contents JJ J where αi = (ai + bi qi )ci , βi = ai ci , and U = Qn Title Page + 1)1/pi ] . Remark 3.1. Remembering our conventions, we observe that, for example, II I Go Back Close Quit 1/qi xi = (x1i )1/qi . . . (xdi )1/qi , n n Y d Y Y 1/qi (αi + 1) = (αij + 1)1/qi . i=1 Page 7 of 18 i=1 j=1 J. Ineq. Pure and Appl. Math. 5(2) Art. 34, 2004 http://jipam.vu.edu.au Proof. Factorize the integrand on the right side of (3.1) as (si − τi )(ai /qi +bi )ci · (si − τi )(ai /pi )ci Φi (τi ) and apply Hölder’s inequality [10, p. 106] and Fubini’s theorem. Then q1 si Z (ai +bi qi )ci |vi (si )| ≤ (si − τi ) i dτi 0 Z × = p1 si 0 (αi +1)/qi si (αi + 1)1/qi a i ci (si − τi ) pi Φi (τi ) dτi si Z Hilbert–Pachpatte Type Multidimensional Integral Inequalities i (si − τi )βi Φi (τi )pi dτi p1 i G.D. Handley, J.J. Koliha and J. Pečarić . 0 Using the inequality of means [10, p. 15] n Y i=1 (α +1)/qi si i ≤ n X Title Page (αi +1)/(qi wi ) wi si Contents , JJ J i=1 we get n Y i=1 where |vi (si )| ≤ W n X i=1 (α +1)/(qi wi ) wi si i n Z Y i=1 si βi pi (si − τi ) Φi (τi ) dτi Go Back p1 i II I , Close 0 1 W = Qn . 1/qi i=1 (αi + 1) Quit Page 8 of 18 J. Ineq. Pure and Appl. Math. 5(2) Art. 34, 2004 http://jipam.vu.edu.au In the following estimate we apply Hölder’s inequality, Fubini’s theorem, and, at the end, change the order of integration: Qn Z x1 Z xn i=1 |vi (si )| ds1 · · · dsn ... Pn (αi +1)/(qi wi ) w s 0 0 i i i=1 "Z # p1 n xi Z s i Y i ≤W (si − τi )βi Φi (τi )pi dτi dsi ≤W i=1 n Y 0 1/q xi i 0 Z i=1 xi Z si βi (si − τi ) Φi (τi ) dτi 0 W = Qn 1/pi i=1 (βi + 1) p1 pi dsi Hilbert–Pachpatte Type Multidimensional Integral Inequalities i 0 n Y i=1 1/q xi i n Z Y i=1 xi βi +1 (xi − τi ) pi Φi (τi ) dτi p1 i . 0 This proves the theorem. Title Page (k) If d = 1 and vi are replaced by the derivatives ui , the preceding theorem reduces to [6, Theorem 3.1]. Corollary 3.2. Under the assumptions of Theorem 3.1, Qn Z x1 Z xn i=1 |vi (si )| (3.3) ... ds1 · · · dsn Pn (αi +1)/(qi wi ) w s 0 0 i i i=1 ! p1 Z xi n n Y 1/q X 1 ≤ p1/p U xi i (xi − si )βi +1 Φ(τi )pi dsi , p i 0 i=1 i=1 where U is given by (3.2). G.D. Handley, J.J. Koliha and J. Pečarić Contents JJ J II I Go Back Close Quit Page 9 of 18 J. Ineq. Pure and Appl. Math. 5(2) Art. 34, 2004 http://jipam.vu.edu.au Proof. By the inequality of means, for any Ai ≥ 0, n Y i=1 1/pi Ai ≤ p1/p n X 1 Ai p i i=1 ! p1 . The corollary then follows from the preceding theorem. The preceding corollary reduces to [6, Corollary 3.2] in the special case (k) when d = 1 and vi are replaced by ui . Hilbert–Pachpatte Type Multidimensional Integral Inequalities G.D. Handley, J.J. Koliha and J. Pečarić Title Page Contents JJ J II I Go Back Close Quit Page 10 of 18 J. Ineq. Pure and Appl. Math. 5(2) Art. 34, 2004 http://jipam.vu.edu.au 4. Applications to Derivatives Convention 1. In this section we shall assume that mi , ki are multiindices satisfying 0 ≤ ki ≤ mi − 1, and write αi = (ai + bi qi )(mi − ki − 1), (4.1) βi = ai (mi − ki − 1). Recall that according to our conventions, mi −ki −1 = (m1i −ki1 −1, . . . , md1 − kid − 1). Theorem 4.1. Let ui ∈ C mi (Q(xi )) be such that Djr ui (si ) = 0 for si ∈ ∂j Q(xi ), 0 ≤ r ≤ mji − 1, 1 ≤ j ≤ d, i ∈ I. Then Z x1 xn Z i=1 ... (4.2) 0 Qn 0 ≤ G.D. Handley, J.J. Koliha and J. Pečarić ki |D ui (si )| ds1 · · · dsn (αi +1)/(qi wi ) i=1 wi si n n Z xi Y Y p 1/qi U1 xi (xi − si )βi +1 Dmi ui (si ) i 0 i=1 i=1 Pn Title Page p1 dsi i , where (4.3) Hilbert–Pachpatte Type Multidimensional Integral Inequalities 1 . 1/qi (β + 1)1/pi ] i i=1 [(mi − ki − 1)!(αi + 1) U1 = Q n Contents JJ J II I Go Back Close Proof. Under the hypotheses of the theorem we have the following multivariable identities established in [11], Z si 1 ki D ui (s) = (si − τi )mi −ki −1 Dmi ui (τi ) dτi , i ∈ I. (mi − ki − 1)! 0 Quit Page 11 of 18 J. Ineq. Pure and Appl. Math. 5(2) Art. 34, 2004 http://jipam.vu.edu.au Inequality (4.2) is proved when we set vi (si ) = Dki ui (si ), ci = mi − ki − 1, and Φi (si ) = (4.4) |Dmi ui (si )| (mi − ki − 1)! in Theorem 3.1. Corollary 4.2. Under the hypotheses of Theorem 4.1, Z x1 Z xn ... (4.5) 0 0 ≤ p1/p U1 Qn ki i=1 |D ui (si )| (αi +1)/(qi wi ) Pn i=1 wi si n Y 1/qi xi i=1 ds1 · · · dsn ! p1 Z xi n X 1 p , (xi − si )βi +1 Dmi ui (si ) i dsi p i=1 i 0 where U1 is given by (4.3). Proof. The result follows by applying the inequality of means to the preceding theorem. Single variable analogues of the preceding two results were obtained in [6, Theorem 4.1] and [6, Corollary 4.2]. We discuss a number of special cases of Theorem 4.1 with similar examples applying also to Corollary 4.2. Hilbert–Pachpatte Type Multidimensional Integral Inequalities G.D. Handley, J.J. Koliha and J. Pečarić Title Page Contents JJ J II I Go Back Close Quit Page 12 of 18 J. Ineq. Pure and Appl. Math. 5(2) Art. 34, 2004 http://jipam.vu.edu.au Example 4.1. If ai = 0 and bi = 1 for i ∈ I, then (4.2) becomes Z x1 Z xn ... (4.6) 0 0 Qn ki i=1 |D ui (si )| ds1 · · · dsn Pn (qi mi −qi ki −qi +1)/(qi wi ) w s i i i=1 n n Z xi Y Y p 1/qi ≤ U1 xi (xi − si )Dmi ui (si ) i 0 i=1 i=1 p1 dsi i , where 1 . 1/qi ] i=1 [(mi − ki − 1)!(qi mi − qi ki − qi + 1) U 1 = Qn (4.7) Example 4.2. If ai = 0, bi = 1, qi = n, wi = n1 , pi = for i ∈ I, then Z x1 Z ... (4.8) 0 0 n , n−1 G.D. Handley, J.J. Koliha and J. Pečarić mi = m and ki = k Qn k i=1 |D ui (si )| Pn nm−nk−n+1 ds1 · · · dsn i=1 si √ n x1 · · · xn 1 ≤ n n [(m − k − 1)!] (n(m − k − 1) + 1) n−1 n Z xi Y n m n n−1 × (xi − si ) D ui (si ) dsi . xn i=1 Hilbert–Pachpatte Type Multidimensional Integral Inequalities 0 Title Page Contents JJ J II I Go Back Close Quit For d = 2 and q = p = n = 2 this is Pachpatte’s theorem [17, Theorem 1] cited in the Introduction; if d = 1 and q = p = n = 2, we obtain [14, Theorem 1]. Page 13 of 18 J. Ineq. Pure and Appl. Math. 5(2) Art. 34, 2004 http://jipam.vu.edu.au Example 4.3. Let ai = 1 and bi = 0 for i ∈ I. Then (4.2) becomes Z x1 Z ... (4.9) 0 Qn xn i=1 |Dki ui (si )| (m −k )/(qi wi ) Pn i i i=1 wi si n n Z Y Y 1/qi e ≤ U1 xi 0 i=1 i=1 xi ds1 · · · dsn mi −ki (xi − si ) p D ui (si ) i dsi mi p1 i , 0 where Hilbert–Pachpatte Type Multidimensional Integral Inequalities 1 . i=1 [(mi − ki − 1)!(mi − ki )] e1 = Qn U (4.10) Example 4.4. Set ai = 0, bi = 1, qi = n, wi = ki = k for i ∈ I. Then (4.2) becomes Z (4.11) 0 x1 1 , n pi = n , n−1 G.D. Handley, J.J. Koliha and J. Pečarić mi = m and Qn k i=1 |D ui (si )| ... Pn m−k ds1 · · · dsn 0 i=1 si √ n x1 · · · xn 1 ≤ n [(m − k − 1)!]n (m − k)n (n−1)/n n Z xi Y n/(n−1) m−k m × (xi − si ) D ui (si ) dsi . Z xn i=1 0 Title Page Contents JJ J II I Go Back Close Quit In the following theorem we establish another inequality similar to the integral analogue of Hilbert’s inequality. Page 14 of 18 J. Ineq. Pure and Appl. Math. 5(2) Art. 34, 2004 http://jipam.vu.edu.au Theorem 4.3. Let ui ∈ C mi +1 (Q(xi )) be such that Dmi ui (si ) = 0 for si ∈ ∂j Q(si ), 1 ≤ j ≤ d, i ∈ I. Then Z x1 Z xn Q n mi i=1 |D ui (si )| (4.12) ... ds1 · · · dsn Pn 1/(qi wi ) w s 0 0 i i i=1 p1 n n Z xi Y Y m +1 pi i 1/qi i ≤ xi (xi − si ) D ui (si ) dsi . i=1 i=1 0 Proof. Under the hypotheses of the theorem we have the following multivariable identities established in [11] for mi = (0, . . . , 0): Z si mi (4.13) D ui (si ) = Dmi +1 ui (τi ) dτi , i ∈ I. 0 In Theorem 3.1 set vi (si ) = Dmi ui (si ), ci = 0, Φi (si ) = |Dmi +1 ui (si )|, and the result follows. 1 , 2 In the special case that d = 2, mi = (0, 0), p = q = n = 2, and wi = the preceding theorem reduces to [17, Theorem 2]. When we apply the inequality of means to the preceding theorem, we get the following corollary which generalizes the inequality obtained in [17, Remark 3]. Corollary 4.4. Under the hypotheses of Theorem 4.3, Z x1 Z xn Q n mi i=1 |D ui (si )| (4.14) ... ds1 · · · dsn Pn 1/(qi wi ) 0 0 i=1 wi si ! p1 Z xi n n Y X 1 p 1/q ≤ p1/p xi i (xi − si )Dmi +1 ui (si ) i dsi . p i 0 i=1 i=1 Hilbert–Pachpatte Type Multidimensional Integral Inequalities G.D. Handley, J.J. Koliha and J. Pečarić Title Page Contents JJ J II I Go Back Close Quit Page 15 of 18 J. Ineq. Pure and Appl. 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