中心极限定理及其初步应用 - 图文(6)

2019-01-10 13:13

理学院毕业(设计)论文 第 26 页

sequencesan?0,bnand a non-degenerate limit distribution G(a so-called max-stable distribution), such that

P(an(Mn?bn)?x)???G(x) (2)

?1(1)w(see, e·g·[6] and [7]), [4] and [5] proved the following result respectively

lim1logNNN???n?11nI?an(Mn?bn)?x??G(x) a.s. (3)

For dependent case, [8] obtained almost sure max-limit theorems of stationary Gaussian

sequence provided its covariance satisfying some regular conditions, later [9] extended the related results to the case of stationary Gaussian vector sequence under some mild conditions on covariance.

Recently [10] studied the almost sure central limit theorem for intermediate order statistics and central order statistics. We are also interested here in the related questions for order statistcs. As before?Xn?is a sequence of i·i·d· random variables with associated order statisticsX1,n?X2,n?...?Xn,n.The joint asymptotic distribution of the first and second largest maximum was obtained by Leadbetter et al. (see[6]), which is the following theorem.

Theorem A LetMn(1)?Xn,n,Mn(2)?Xn?1,ndenote, respectively, the first and the second largest maximum of?X1,X2,...,Xn?and suppose that (2) holds, then for x>y,

P(an(Mn?bn)?x,an(Mn?1(1)?1(2)?bn)?y)???G(y)?logG(x)?logG(y)?1? (4)

wwhen G(y) >0 (and to zero if G(y) =0).

The purpose of this paper is to obtain an almost sure version of Theorem 2·3·1 of [6]. Since the mere existence of the weak limit does not always imply the almost sure limiting result for the logarithmic averages (see [3]), the investigation of a general almost sure limit theorem seems somewhat challenging.

2 Main results

In this section we are interested in the almost sure central limit theorems of random vector(Mn(1),Mn(2)).The main results are provided here and all proof are deferred to Section 3. For convenience, in the rest of the paper, we denote

un?un(x)?anx?bn,vn?vn(y)?any?bn

Theorem 1 Let ?Xn?be a sequence of i·i·d· random variables, Mn(1),Mn(2)denote, respectively, the first and the second largest maximum, and assume (2) hold, then for x > y

理学院毕业(设计)论文 第 27 页

1logNNN??lim?nI{an?11?1n(Mn?bn)?x,an(Mn?bn)?y}?G(y)?logG(x)?logG(y)?1? a.s.

(1)?1(2) (5)

as G(y) >0 (and to zero if G(y) =0).

Based on Theorem 1, we derived the well-known almost sure central limit theorem of the maximum of the original i·i·d· random variables{Xn},which, as we have mentioned, was firstly provided by [4] and [5].

Corollary 1 Under the conditions of Theorem 1, for all real x we have

N??lim1logNN?n?11nI?an(Mn?1(1)?bn)?x??G(x) a.s. (6)

Following corollary extended the desired result to bounded Lipschitz function case. corollary 2 Let{Xn}be a sequence of i·i·d·random variables, assume also that f(x, y)is a bounded Lipschitz 1 function, Then under the condition of Theorem 1, we have

N??lim1logNN?n?11nf(an(M?1(1)n?bn),an(M?1(2)n??bn))???f(x,y)dG(x,y) a.s. (7)

where G(x,y)?G(y){logG(x)?logG(y)?1}

?3 Proofs

We need some technique to prove our main results. Following lemma will be crucial in the whole proof of our main theorem.

Lemma 1 Let ??n?be a sequence of bounded random variables. If

NVar(?n?11n?n)?(logN)2??, (8)

Then

NVar(?n?11n(?n?E?n)?0a.s. (9)

Proof See Lemma 1 in [5].

(2)Lemma 2 Let{Xn}be a sequence of i·i·d·random variables, andMn(2),Mmdenote, ,nrespectively, the second largest maximum of{X1,...Xm}and{Xm?1,...Xn}then

m?2?(2)?Mm,n)??n?1,n?m?2,m?1

?1,其它?P(Mn(2)(2))?1 when n-m<2.Forn-m≥2,we calculate the Proof It is clear that P(Mn(2)?Mm,n 理学院毕业(设计)论文 第 28 页

probability of the complement. Note that the sequence ?Xn?is i·i·d·, we have

P(Mn(2)?Mm,n)?(n?m)P(Xn???1?2(2)m?1?v?n?1max{Xv}?max{Xj})1?j?m?(n?m)????dF(t)dF(?2)mn?1?mdF(?1)

??????(n?m)(n?m?1)n(n?1)Therefore, we obtain

P(Mn(2)?Mm,n)?1?mn)(1?2(2)(n?m)(n?m?1)n(n?1)?1?(1??1?(1?nmn?1)m

mn?1ni)?2n?1nby the elementary fact that

?x??i?1i?1yi??i?1xi?yihold for xi?1,yi?1.The result

follows. Let us denote?n?I{Mn(1)?un,Mn(2)?vn}?P{Mn(1)?un,Mn(2)?vn} Following pivotal lemma is estimating the bound of the covariance of {?n} Lemma 3 Under the conditions of Theorem 1, for n-m?2 we have

Cov(?m,?n)?mn?1

Proof By elementary calculations, for m < n we have

Cov(?m,?n)?Cov(I{Mm?um,Mm?vm},I{Mn?un,Mn(1)(2)(1)(2)?vn})

?EI{Mn?un,MnEI{M(1)n(1)(2)?vn}?I{Mn?un,Mm,n?vn}?(1)m,n(1)(2) (10)

?un,M(1)(2)m,n?vn}?I{M(2)?un,M(1)(2)m,n?vn}?(2)Cov(I{Mm?um,Mm?vm},I{Mm,n?um,Mm,n?vm})?A1?A2?A3Note that A3=0 by independence of?Xn?,our task now is to estimate the upper bound ofA1 and A2 in (10).

By the same statement of [3], p. 123, for1?m?n we have

理学院毕业(设计)论文 第 29 页 A2?EI{Mn?un}?I{Mm,n?un}I{Mm,n?vn}(1)(1)(2) ?EI{Mn?un}?I{Mm,n?un}?P(Mn?Mm,n)?(1)(1)(1)(1) (11)

mnNow it remains to estimate the bound of component A1,by using Lemma 2, for n-m?2, we have

A1?EI{Mn(2)(2)(2)?un}?I{Mm,n?un}?P(Mm?Mm,n)?P(Mn(2)(2) (12)

mn?1?Mm,n)?2(2)Relations (10), (11), (12) yield the desired result.

Proof of Theorem 1 By Lemma 1, we only need to estimate the bound of weighted sum of??n?.Notice that

12Var(??n)?E(??n)n?1nn?1nNN1N??n?11nE?n?222?1?m?n?N1mnE?m?n (13)

?B1?B2Since?n?2,we have

?B1??n?11n2?? (14)

Now we start to estimate component B2.By Lemma 3, we have

B2??1?m?n?Nn?m?21mn??1?m?n?Nn?m?21mmnn?1

?logN (15)

Now relations (13)-(15), combined with Lemma 1, imply the desired result.

Proof of Corollary 1 Observing that for any ??0the following inequalities hold:

I{Mn?anx?bn}?I{Mn?an(x??)?bn,MnI{M(1)n(1)(1)(2)?anx?bn}?anx?bn}?I{M(1)n?anx?bn,M(2)n?an(x??)?bn}

Therefore, by using Theorem 1, we have

理学院毕业(设计)论文 第 30 页

1logN1logNNN??limsupliminf?n?1N1n1nI{an(Mn?bn)?x}?G(x??){logG(x)?logG(x??)?1}?1(1) (16)

I{an(Mn?bn)?x}?G(x){logG(x??)?logG(x)?1}?1(1)N???n?1Noting the continuity of G(x),we complete the proof by letting??0 in (16). Proof of Corollary 2 The Proof of Corollary 2 is similar to Theorem 1.

References:

[1] Brosamler G. An Almost Everywhere Central Limit Theorem [J]. Math Proc Cambridge Philos Soc, 1988, 104(3): 561

[2] Schatte P. On Strong Versions of the Central Limit Theorem [J]. Math Nachr, 1988, 137: 249-256.

[3] Berkes I, Csáki E. A Universal Result in Almost Sure Central Limit Theory [J]. Stochastic Process Appl, 2001, 94(1): 105-134.

[4] Cheng S, Peng L, Qi Y. Almost Sure Convergence in Extreme Value Theory [J]. Math Nachr, 1998, 190: 43-50. [5] Fahrner I, Stadtmüller U. On Almost Sure Max-limit Theorems [J]. Statist Probab Lett, 1998, 37(3): 229-236.

[6] Leadbetter M R, Lindgren G, Rootzén H. Extremes and Related Properties of Random Sequences and Processes [M]. Berlin: Springer, 1983.

[7] Resnick S I. Extreme Values, Regular Variation and Point Processes [M]. Berlin: Springer, 1987. [8] Csáki E, Gonchigdanzan K. Almost Sure Limit Theorems for the Maximum of Stationary Gaussian Sequences [J]. Stat- ist Probab Lett, 2002, 58(2): 195-203.

[9] 陈志成,彭作祥.平稳高斯向量序列最大值的几乎处处中心极限定理[J].西南大学学报(自然科学版), 2007, 29(3): 23-27.

[10] Stadtmüller U. Almost Sure Versions of Distributional Limit Theorems for Certain Order Statistics [J]. Statist Probab Lett, 2002, 58: 413-426.


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