Hindawi Publishing Corporation Discrete Dynamics in Nature and Society Volume 2011, Article ID 717126, 11 pages doi:10.1155/2011/717126 Research Article Complete Convergence for Arrays of Rowwise Asymptotically Almost Negatively Associated Random Variables Xuejun Wang, Shuhe Hu, and Wenzhi Yang School of Mathematical Science, Anhui University, Hefei 230039, China Correspondence should be addressed to Xuejun Wang, 07019@ahu.edu.cn Received 24 April 2011; Revised 3 September 2011; Accepted 18 September 2011 Academic Editor: Wei-Der Chang Copyright q 2011 Xuejun Wang et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. Let {Xni , i ≥ 1, n ≥ 1} be an array of rowwise asymptotically almost negatively associated random variables. Some sufficient conditions for complete convergence for arrays of rowwise asymptotically almost negatively associated random variables are presented without assumptions of identical distribution. As an application, the Marcinkiewicz-Zygmund type strong law of large numbers for weighted sums of asymptotically almost negatively associated random variables is obtained. 1. Introduction The concept of complete convergence was introduced by Hsu and Robbins 1 as follows. A sequence of random variables {Un , n ≥ 1} is said to converge completely to a constant C if ∞ n1 P |Un − C| > ε < ∞ for all ε > 0. In view of the Borel-Cantelli lemma, this implies that Un → C almost surely a.s.. The converse is true if the {Un , n ≥ 1} are independent. Hsu and Robbins 1 proved that the sequence of arithmetic means of independent and identically distributed i.i.d. random variables converges completely to the expected value if the variance of the summands is finite. Since then many authors studied the complete convergence for partial sums and weighted sums of random variables. The main purpose of the present investigation is to provide the complete convergence results for weighted sums of asymptotically almost negatively associated random variables and arrays of rowwise asymptotically almost negatively associated random variables. Firstly, let us recall the definitions of negatively associated and asymptotically almost negatively associated random variables. 2 Discrete Dynamics in Nature and Society Definition 1.1. A finite collection of random variables X1 , X2 , . . . , Xn is said to be negatively associated NA, in short if for every pair of disjoint subsets A1 , A2 of {1, 2, . . . , n}, Cov fXi : i ∈ A1 , g Xj : j ∈ A2 ≤ 0, 1.1 whenever f and g are coordinatewise nondecreasing such that this covariance exists. An infinite sequence {Xn , n ≥ 1} is NA if every finite subcollection is negatively associated. An array of random variables {Xni , i ≥ 1, n ≥ 1} is called rowwise NA random variables if, for every n ≥ 1, {Xni , i ≥ 1} is a sequence of NA random variables. The concept of negative association was introduced by Joag-Dev and Proschan 2. By inspecting the proof of maximal inequality for the NA random variables in Matula 3, one also can allow negative correlations provided they are small. Primarily motivated by this, Chandra and Ghosal 4, 5 introduced the following dependence. Definition 1.2. A sequence {Xn , n ≥ 1} of random variables is called asymptotically almost negatively associated AANA, in short if there exists a nonnegative sequence qn → 0 as n → ∞ such that 1/2 , Cov fXn , gXn1 , Xn2 , . . . , Xnk ≤ qn Var fXn Var gXn1 , Xn2 , . . . , Xnk 1.2 for all n, k ≥ 1 and for all coordinatewise nondecreasing continuous functions f and g whenever the variances exist. An array of random variables {Xni , i ≥ 1, n ≥ 1} is called rowwise AANA random variables if, for every n ≥ 1, {Xni , i ≥ 1} is a sequence of AANA random variables. The family of AANA sequence contains NA in particular, independent sequences with qn 0, n ≥ 1 and some more sequences of random variables which are not much deviated from being negatively associated. An example of an AANA sequence which is not NA was constructed by Chandra and Ghosal 4. Since the concept of AANA sequence was introduced by Chandra and Ghosal 4, many applications have been found. See, for example, Chandra and Ghosal 4 derived the Kolmogorov type inequality and the strong law of large numbers of MarcinkiewiczZygmund, Chandra and Ghosal 5 obtained the almost sure convergence of weighted averages, Ko et al. 6 studied the Hájek-Rényi type inequality, Wang et al. 7 established the law of the iterated logarithm for product sums, Yuan and An 8 established some Rosenthal type inequalities for maximum partial sums of AANA sequence, and Wang et al. 9 obtained some strong growth rate and the integrability of supremum for the partial sums of AANA random variables, and so forth. Our goal in this paper is to study the complete convergence for arrays of rowwise AANA random variables under some moment conditions. As an application, the Marcinkiewicz-Zygmund type strong law of large numbers for weighted sums of AANA random variables is obtained. We will give some sufficient conditions for complete convergence for an array of rowwise AANA random variables without assumption of identical distribution. The results presented in this paper are obtained by using the truncated method and the classical maximal type inequality of AANA random variables Lemma 1.5 below. Discrete Dynamics in Nature and Society 3 Throughout the paper, let {Xni : i ≥ 1, n ≥ 1} be an array of rowwise AANA random . variables with the mixing coefficients {qi, i ≥ 1} in each row. For p > 1, let q p/p − 1 be the dual number of p. Let IA be the indicator function of the set A. C denotes a positive constant which may be different in various places and an Obn stands for an ≤ Cbn . Definition 1.3. An array of random variables {Xni , i ≥ 1, n ≥ 1} is said to be stochastically dominated by a random variable X if there exists a positive constant C such that P |Xni | > x ≤ CP |X| > x 1.3 for all x ≥ 0, i ≥ 1 and n ≥ 1. The following lemmas are useful for the proofs of the main results. Lemma 1.4 cf. Yuan and An 8, Lemma 2.1. Let {Xn , n ≥ 1} be a sequence of AANA random variables with mixing coefficients {qn, n ≥ 1}, let f1 , f2 , . . . be all nondecreasing (or all nonincreasing) functions, then {fn Xn , n ≥ 1} is still a sequence of AANA random variables with mixing coefficients {qn, n ≥ 1}. Lemma 1.5 cf. Yuan and An 8, Theorem 2.1. Let {Xn , n ≥ 1} be a sequence of AANA random variables with EXi 0 for all i ≥ 1 and p ∈ 3 · 2k−1 , 4 · 2k−1 , where integer number k ≥ 1. If ∞ q/p n < ∞, then there exists a positive constant Dp depending only on p such that for all n1 q n ≥ 1, j p p/2 n n p 2 E|X EX . E max i1 Xi ≤ Dp | i i i1 i1 1≤j≤n 1.4 Lemma 1.6. Let {Xn , n ≥ 1} be a sequence of random variables which is stochastically dominated by a random variable X. For any α > 0 and b > 0, the following two statements hold: E|Xn |α I|Xn | ≤ b ≤ C1 E|X|α I|X| ≤ b bα P |X| > b , 1.5 E|Xn |α I|Xn | > b ≤ C2 E|X|α I|X| > b, 1.6 where C1 and C2 are positive constants. 2. Main Results Let {Xni : i ≥ 1, n ≥ 1} be an array of rowwise AANA random variables with the mixing coefficients {qi, i ≥ 1} in each row, and let {ani : i ≥ 1, n ≥ 1} be an array of real numbers. Let {Xi , i ≥ 1} be a sequence of AANA random variables with the mixing coefficients {qi, i ≥ 1} and let {ai , i ≥ 1} be a sequence of real numbers. We consider the following conditions. H1 There exist some δ with 0 < δ < 1 and some α with 0 < α < 2 such that ni1 |ani |α Onδ , and assume further that EXni 0 if 1 < α < 2. q/p H2 There exists some p ∈ 3 · 2k−1 , 4 · 2k−1 such that ∞ i < ∞, where integer i1 q number k ≥ 1. 4 Discrete Dynamics in Nature and Society H3 For some h > 0 and γ > 0, E exp h|X|γ < ∞. 2.1 H4 There exist some δ with 0 < δ < 1 and some α with 0 < α < 2 such that ni1 |ai |α Onδ , and assume further that EXn 0 if 1 < α < 2. H5 There exists some α with 0 < α < 2 such that ni1 |ani |α On and assume further that EXni 0 if 1 < α < 2. H6 There exists some α with 0 < α < 2 such that ni1 |ai |α On and assume further that EXn 0 if 1 < α < 2. Our main results are as follows. Theorem 2.1. Let {Xni : i ≥ 1, n ≥ 1} be an array of rowwise AANA random variables which is stochastically dominated by a random variable X, and let {ani : i ≥ 1, n ≥ 1} be an array of real numbers. Suppose that the conditions (H1 )–(H3 ) are satisfied. Then, for any ε > 0, j sα−2 > εb n P max a X < ∞, ni ni n n1 i1 ∞ 2.2 1≤j≤n . where s ≥ 1/α and bn n1/α log1/γ n. Proof. For fixed n ≥ 1, define n Xi −bn IXni < −bn Xni I|Xni | ≤ bn bn IXni > bn , j n n n X , j 1, 2, . . . , n. a − EX Tj ni i i i1 i ≥ 1, 2.3 It is easy to check that for any ε > 0, j j n max i1 ani Xni > εbn ⊂ max|Xni | > bn max i1 ani Xi > εbn , 1≤j≤n 1≤i≤n 1≤j≤n 2.4 which implies that j P max i1 ani Xni > εbn 1≤j≤n j n ≤ P max|Xni | > bn P max i1 ani Xi > εbn 1≤i≤n ≤ 1≤j≤n j n n P |Xni | > bn P max Tj > εbn − max i1 ani EXi . i1 n 1≤j≤n 1≤j≤n 2.5 Discrete Dynamics in Nature and Society 5 Firstly, we will show that j n bn−1 max i1 ani EXi −→ 0, 1≤j≤n By n i1 |ani | α as n −→ ∞. 2.6 Onδ and Hölder’s inequality, we have for 1 ≤ k < α that n k |a | ≤ i1 ni n i1 |ani | k α/k k/α n α−k/α 1 ≤ Cn. i1 2.7 Hence, when 1 < α < 2, we have by EXni 0, 1.6 of Lemma 1.6, 2.7 taking k 1, Markov’s inequality, and 2.1 that j n j n −1 max a EX I|X b > b > b bn−1 max i1 ani EXi ≤ |X |a |P | | ni ni n ni ni ni n n i1 i1 1≤j≤n 1≤j≤n n n |ani |P |X| > bn bn−1 i1 |ani |E|Xni |I|Xni | > bn n E exp h|X|γ ≤ Cn γ Cbn−1 i1 |ani |E|X|I|X| > bn exp hbn ≤C i1 Cn Cbn−1 nE|X|I|X| > bn γ/α nhn ∞ Cn Cbn−1 n kn E|X|Ibk < |X| ≤ bk1 γ/α hn n ∞ Cn ≤ Cbn−1 n kn bk1 P |X| > bk γ/α nhn ∞ E exp h|X|γ Cn −1 ≤ Cbn n kn bk1 γ γ/α nhn exp hbk ≤ ∞ 1/γ −hkγ/α Cn Cbn−1 n kn k 11/α logk 1 k γ/α hn n ∞ 1/γ −hkγ/α Cn ≤ Cbn−1 kn k 11/α1 logk 1 k γ/α hn n ≤ ≤ −1/γ Cn Cn−1/α log n −→ 0, γ/α nhn as n −→ ∞. 2.8 Elementary Jensen’s inequality implies that for any 0 < s < t, n |a |t i1 ni 1/t ≤ n |a |s i1 ni 1/s . 2.9 6 Discrete Dynamics in Nature and Society Therefore, when 0 < α ≤ 1, we have by 1.5 of Lemma 1.6, 2.9, Markov’s inequality, and 2.1 that j n n n bn−1 max i1 ani EXi ≤ |a |P |Xni | > bn bn−1 i1 |ani |E|Xni |I|Xni | ≤ bn i1 ni 1≤j≤n ≤C n i1 Cbn−1 |ani |P |X| > bn n i1 |ani |E|X|I|X| ≤ bn bn P |X| > bn ≤ Cbn−1 nδ/α E|X|I|X| ≤ bn Cnδ/α P |X| > bn ≤ Cbn−1 nδ/α ≤ Cbn−1 nδ/α ≤ Cbn−1 nδ/α ≤ Cbn−1 nδ/α n k2 E|X|Ibk−1 Cnδ/α E exp h|X|γ < |X| ≤ bk γ exp hbn n b P |X| > bk−1 k2 k Cnδ/α γ/α nhn E exp h|X|γ Cnδ/α b γ γ/α k2 k nhn exp hbk−1 n n k2 γ/α k1/α log k1/γ k − 1−hk−1 Cnδ/α γ/α nhn −1/γ δ/α Cnδ/α ≤ Cn−1/α log n n γ/α nhn Clog n−1/γ nδ/α−1/α Cnδ/α −→ 0, γ/α nhn as n −→ ∞. 2.10 By 2.8 and 2.10, we can get 2.6 immediately. Hence, for n large enough, j n n ε P max i1 ani Xni > εbn ≤ b > P . P max > b |X | T ni n n i1 1≤j≤n 1≤j≤n j 2 2.11 To prove 2.2, we only need to show that . ∞ sα−2 n I n P |Xni | > bn < ∞, n1 i1 . ∞ sα−2 n ε n P max Tj > bn < ∞. J n1 1≤j≤n 2 2.12 Discrete Dynamics in Nature and Society 7 By Definition 1.3, Markov’s inequality and 2.1, we can see that . ∞ sα−2 n I n P |Xni | > bn n1 i1 ≤C ≤C ≤C ∞ nsα−2 n1 ∞ n1 sα−1 n n i1 P |X| > bn E exp h|X|γ γ exp hbn ∞ nsα−1 < ∞. n1 hnγ/α n 2.13 n For fixed n ≥ 1, it is easily seen that {Xi , 1 ≤ i ≤ n} are still AANA random variables by Lemma 1.4. For r > 2, it follows from Lemma 1.5, Cr ’s inequality, and Jensen’s inequality that . ∞ sα−2 n ε J n P max Tj > bn n1 1≤j≤n 2 ∞ n r sα−2 −r bn E max Tj ≤ C n2 n 1≤j≤n ≤C ≤C ∞ nsα−2 bn−r n2 ∞ nsα−2 bn−r n2 n r/2 n n r n 2 2 n E − EX E − EX |a | Xi |a | Xi i i i1 ni i1 ni n r 2 r/2 ∞ n n r 2 n sα−2 −r bn |a | E Xi C n2 n |a | E Xi i1 ni i1 ni n r . J1 J2 . 2.14 Taking r > max{2, αsα − 1/1 − δ}, which implies that r > α. It follows from Cr ’s inequality, 1.5 of Lemma 1.6, 2.9, Markov’s inequality, and 2.1 that n . ∞ n r J1 C n2 nsα−2 bn−r i1 |ani |r E Xi ≤C ∞ nsα−2 bn−r n2 ∞ n i1 |ani |r E|Xni |r I|Xni | ≤ bn bnr P |Xni | > bn n |ani |r E|X|r I|X| ≤ bn bnr P |X| > bn ∞ ∞ ≤ C n2 nsα−2rδ/α bn−r E|X|r I|X| ≤ bn C n2 nsα−2rδ/α P |X| > bn ≤C ≤C ≤C nsα−2 bn−r n2 ∞ i1 nsα−2rδ/α bn−r n2 ∞ ∞ k2 n k2 γ E|X| Ibk−1 < |X| ≤ bk C ∞ n2 sα−2rδ/α n E exp h|X|γ γ exp hbn ∞ nsα−2rδ/α −r/γ r sα−2rδ/α −r/α n n b P > b C log n |X| k−1 γ/α k nk n2 nhn 8 Discrete Dynamics in Nature and Society ≤C ≤C ∞ br k2 k ∞ nsα−2rδ/α E exp h|X|γ γ C n2 γ/α nhn exp hbk−1 ∞ kr/α log k r/γ k2 γ/α k − 1hk−1 C ∞ nsα−2rδ/α < ∞. γ/α n2 nhn 2.15 By Cr ’s inequality, 1.5 of Lemma 1.6, 2.9, and Jensen’s inequality, we can get that 2 r/2 n . ∞ 2 n J2 C n2 nsα−2 bn−r |a | E Xi i1 ni ≤C ≤C ≤C ≤C ≤C r/2 2 2 2 E|X |a | I|X P b ≤ b > b |X | | | ni ni ni n ni n n i1 ∞ n ∞ n nsα−2 bn−r n2 nsα−2 bn−r n2 r/2 2 2 2 EX I|X| ≤ b b P > b |X| |a | ni n n n i1 r/2 sα−2rδ/α −r 2 2 EX n b I|X| ≤ b P > b b |X| n n n n n2 ∞ r/2 ∞ sα−2rδ/α −r 2 EX n b I|X| ≤ b C nsα−2rδ/α P |X| > bn r/2 n n n2 n2 ∞ ∞ <∞ nsα−2rδ/α bn−r E|X|r I|X| ≤ bn C n2 ∞ n2 nsα−2rδ/α P |X| > bn see the proof of 2.15 . 2.16 Therefore, the desired result 2.2 follows from 2.13–2.16 immediately. This completes the proof of the theorem. Similar to the proof of Theorem 2.1, we can get the following result for sequences of AANA random variables. Theorem 2.2. Let {Xn , n ≥ 1} be a sequence of AANA random variables which is stochastically dominated by a random variable X, and let {ani , i ≥ 1, n ≥ 1} be an array of real numbers. Suppose that the conditions (H1 )–(H3 ) are satisfied (EXni 0 is replaced by EXn 0 in H1 ). Then, for any ε > 0, j sα−2 > εb < ∞, n P max a X i1 ni i n n1 ∞ 1≤j≤n 2.17 . where s ≥ 1/α and bn n1/α log1/γ n. The following result provides the Marcinkiewicz-Zygmund type strong law of large numbers for weighted sums ni1 ai Xi of AANA sequence of random variables. Discrete Dynamics in Nature and Society 9 Theorem 2.3. Let {Xn , n ≥ 1} be a sequence of AANA random variables which is stochastically dominated by a random variable X and {an , n ≥ 1} be a sequence of real numbers. Suppose that the conditions (H2 )–(H4 ) are satisfied. Then for any ε > 0, ∞ n1 sα−2 n P max Sj > εbn 1≤j≤n Sn lim n → ∞ bn < ∞, 2.18 2.19 0 a.s., . where s ≥ 1/α, bn n1/α log1/γ n and Sn ni1 ai Xi for n ≥ 1. Proof. Similar to the proof of Theorem 2.1, we can get 2.18 immediately, which yields that −1 Sj > εbn < ∞. n P max n1 ∞ 2.20 1≤j≤n Therefore, ∞> −1 Sj > εbn n P max n1 ∞ 1≤j≤n ∞ 2i1 −1 i0 n2i 1 ∞ ≥ P 2 i1 1/γ n−1 P max Sj > εn1/α log n 1≤j≤n 1/γ max Sj > ε2i1/α log 2i1 1≤j≤2i 2.21 . By Borel-Cantelli lemma, we obtain that max1≤j≤2i Sj lim 1/γ 0 a.s. i → ∞ i1/α 2 log 2i1 2.22 For all positive integers n, there exists a positive integer i0 such that 2i0 −1 ≤ n < 2i0 . We have by 2.22 that 22/α max1≤j≤2i Sj i0 1 1/γ |Sn | |Sn | ≤ max ≤ −→ 0 a.s., as i0 −→ ∞, 1/γ i − 1 bn 2i0 −1 ≤n<2i0 bn 0 2i0 1/α log 2i0 1 2.23 which implies 2.19. This completes the proof of the theorem. Remark 2.4. In Theorems 2.1–2.3, the condition H1 or H4 is needed. Under the weaker condition H5 or H6 than H1 or H4 , we can get the following Theorems 2.5–2.7. The details of their proofs are omitted. 10 Discrete Dynamics in Nature and Society Theorem 2.5. Let {Xni : i ≥ 1, n ≥ 1} be an array of rowwise AANA random variables which is stochastically dominated by a random variable X, and let {ani : i ≥ 1, n ≥ 1} be an array of real numbers. Suppose that the conditions (H2 ), (H3 ), and (H5 ) are satisfied. Then, for any ε > 0, j −1 > εb n P max a X < ∞, n n1 i1 ni ni ∞ 1≤j≤n 2.24 . where bn n1/α log1/γ n. Theorem 2.6. Let {Xn , n ≥ 1} be a sequence of AANA random variables which is stochastically dominated by a random variable X, and let {ani , i ≥ 1, n ≥ 1} be an array of real numbers. Suppose that the conditions (H2 ), (H3 ) and (H5 ) are satisfied (EXni 0 is replaced by EXn 0 in (H5 )). Then, for any ε > 0, j −1 > εb < ∞, n P max a X i1 ni i n n1 ∞ 1≤j≤n 2.25 . where bn n1/α log1/γ n. Theorem 2.7. Let {Xn , n ≥ 1} be a sequence of AANA random variables which is stochastically dominated by a random variable X, and let {an , n ≥ 1} be a sequence of real numbers. Suppose that the conditions (H2 ), (H3 ), and (H6 ) are satisfied. Then, for any ε > 0, ∞ n P max Sj > εbn n1 −1 1≤j≤n Sn lim 0 a.s., n → ∞ bn < ∞, 2.26 . where bn n1/α log1/γ n and Sn ni1 ai Xi for n ≥ 1. Acknowledgments The authors are most grateful to the Editor Wei-Der Chang and anonymous referees for careful reading of the paper and valuable suggestions which helped in improving an earlier version of this paper. This work was supported by the NNSF of China 11171001, Provincial Natural Science Research Project of Anhui Colleges KJ2010A005, Talents Youth Fund of Anhui Province Universities 2010SQRL016ZD, Youth Science Research Fund of Anhui University 2009QN011A, and the academic innovation team of Anhui University KJTD001B. References 1 P. L. Hsu and H. Robbins, “Complete convergence and the law of large numbers,” Proceedings of the National Academy of Sciences of the United States of America, vol. 33, pp. 25–31, 1947. 2 K. Joag-Dev and F. Proschan, “Negative association of random variables, with applications,” The Annals of Statistics, vol. 11, no. 1, pp. 286–295, 1983. Discrete Dynamics in Nature and Society 11 3 P. Matuła, “A note on the almost sure convergence of sums of negatively dependent random variables,” Statistics & Probability Letters, vol. 15, no. 3, pp. 209–213, 1992. 4 T. K. Chandra and S. Ghosal, “Extensions of the strong law of large numbers of Marcinkiewicz and Zygmund for dependent variables,” Acta Mathematica Hungarica, vol. 71, no. 4, pp. 327–336, 1996. 5 T. K. Chandra and S. Ghosal, “The strong law of large numbers for weighted averages under dependence assumptions,” Journal of Theoretical Probability, vol. 9, no. 3, pp. 797–809, 1996. 6 M.-H. Ko, T.-S. Kim, and Z. Lin, “The Hájeck-Rènyi inequality for the AANA random variables and its applications,” Taiwanese Journal of Mathematics, vol. 9, no. 1, pp. 111–122, 2005. 7 Y. Wang, J. Yan, F. Cheng, and C. Su, “The strong law of large numbers and the law of the iterated logarithm for product sums of NA and AANA random variables,” Southeast Asian Bulletin of Mathematics, vol. 27, no. 2, pp. 369–384, 2003. 8 D. Yuan and J. An, “Rosenthal type inequalities for asymptotically almost negatively associated random variables and applications,” Science in China. Series A: Mathematics, vol. 52, no. 9, pp. 1887– 1904, 2009. 9 X. J. Wang, S. H. Hu, and W. Z. Yang, “Convergence properties for asymptotically almost negatively associated sequence,” Discrete Dynamics in Nature and Society, vol. 2010, Article ID 218380, 15 pages, 2010. 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