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什么是不等式【关于Carlson不等式】

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第28卷第5期2007年9月

吉首大学学报(自然科学版)

Jmtmal0fJishou

V01.28

No.5

Univendty(NatundSci∞DeEdition)

Sept.2007

Artide玎D:1007—2985(2007)05—0024—03

OntheCarlsonInequanty

(1・Depa舳ntofMathematicsandComptlter,NormalCollegeofJishouUniversity,Jishou416000,Hlm舳chim;2.伽e学e

Mathematics

SHIYan-pin91,SHANGXiao-zhoul,HE

k.pi《

andComputerScience,JishouUniversity,Jishou

416000,Hll瑚n‰)

of

Abstract:AnimprovementoftheLandautnequaUtyi8establishedby

Carlsoninequalityisstrengthened.

sharpeningofCauchy’sineqIIali妙.And此

Keywords:Carlsoninequality;Landauinequality;innerproduct;norm

Q£nmnber:0178

I)ocmnent∞de:A

1IntroductionandLet{%}be

the

Results

sequence

ofnonnegativerealnumbe玛.

IfO<∑,12口2<+∞,then

n=1

。∑Ⅲ

Thisir】eqllalit),iscalledCarlsoninequality【1J.

‰r≤f

。∑Ⅲ

:%

。∑Ⅲ

(1)

Mterwards,Landau

andHardygave

sonle

improvements

of(1)and

ledto

lotofresultsoflegance.One0f

tll锄

isLandauinequalityoftheform

then

an

。∑Ⅲ

r≤一

。∑删

:%

.妻(凡一{)z%2

rt=1

(2)

‘i軎扎扩;岫妇坶

of(2)will

be

isthe

一脚一

inequality(1).Inthis

㈣删

删池

f客口李n一枷2。_

obtained.So

paper,wewillprovethe

improvement

exi8ter耽ofR2

andwillgivetheexpressionofit.More

precisely,wehavethefollowingresults.

∑/12口:<+∞,then

n=】

(∑‰)4

^=1

<f蚤口:∑(n—i)2”R2,

n=l

nffil

-1

(3)

whereR2

=2(客口:杰n=l口n一妻n=l叫1't2喀2矿南]2.

c凡

Yah-ping(1978一),female,W88

borninLongshan

County,Hunan

theoryandordinarydifferential

・Receiveddate:20(Y/一01—08

fU/枷OH

嘲:Sift

dI删删.

Province,as8i删;mjor黜h6龇啪剐

第5期

IfR2containedNoticethat

石艳平:关于‰不等式

in(3)is

replacedbyzero,thentheLandauinequalityisyielded.

25

o:.∑(n一了1,2口2。s∑n2一、”,,,”^、厶…n‘

n=1

^=1

HenceWehave:

C(dh眄1

Withtheassumptions鹅theorem1,then

(∑口。)4≤7c2∑口:∑n2o:二R2,

whereR2isgive.bytheorem1.

As

an

application.WecomidertheHilbertinequalityoftheform

(荟。而arabn).2≤7c2∑n=l。:∑n=l

wherethe

6:,

we

(4)

havethefollo诵ngresult:

constant齐in(4)wasprovedtobebestpossible‘2—3J.Letb。=嬲。.Then

Corollary2

Withtheassumptions够theorem1.then

(煮,等等)≤{(7c2杰n=l口2。著n2—2㈣,

whereR2isgivenbytheorem1.

Proof

Since

(5)

h饥∞

一弋■一厶

m.n=1

a揣=2羔。嚣,

m.n2I

。∑一

We

型m坠忍

.一+

II

l一2

。∑Ⅲ

7c2of(4)is

not

Bycorollary1,the

see

inequality(5)follows.

theconstant

bestpossibleundersuch

case.

from(5)that

2ProofofTheorem1

Toprovetheorem1,WeneedtointroduceIf口and

8叫Tle

conceptsandnotatiom.

of口isgiventhe

rlolln

by忆II=佩.Furthermore,if口=(%)。》1

are

elements

of锄inner

productspaceE,thenitsinnerproductisdenoted

are

by(a,p)and

the

nornl

two

real∞qllences,thenitsinnerproductand

of口aredefinedby

(d,卢)=∑%b。,ff口f|=(∑o:)∽.

n;1

n=1

Analogously,forfunctionsf,g∈L2(n,b),itsinnerproductandthe

noIl'n

off

are

definedby

(f,g)=I以f)g(t)dt,fff|f=(I尸(t)dt)垅.

√口

(6)

We

nextintroduce

binaryquadraticformdefinedby

r(x,Y)=忆JJ2菇2—2(口,卢)缈+JJ刚2,,2,

where龙=(p,y)andy=(口,y)fory∈E试tllI|yI|=1.

Ⅵkflll曲erdenote

(7)

G(口,p,7)=F((p,7),(口,y)).

TheresultsinvolveG(口,卢,),)诵tIl口and卢specifiedbeforehand,and7

obviousthatifyisorthogonaltoboth口and

to

(8)

bechosenformaximumfelicity.Itis

p,thenG(O/,p,y)=0.It

willturnoutthat

if(口,y)2+(口,7)2>0

(Seelemma2).Therefore,itisshrewdinevery

c跚to

choose7notorthogonaltoboth口and口.

Thefollowinglemmaswillbeusefulintheproofoftheorem1.

Le咖m

Let

o≤a<b.Iff(t)is

derivable

in(a,b)and.厂(b)=0,then

吉首大学学报(自然科学版)第28卷

八口)=一2I八t)f(t)dt.

(9)

Proof

Bythehypothesis,wehave

一2I八t)f(t)dt=一I(尸(f))7dt=一(尸(6)一尸(口))=尸(口).

Llmmm2

Let

G(a,p,y)be

defined

as

in(8).Ifa,p∈E

are

linearlyindependent

and(a,y)2+(p,y)2

>0,then

G(口,卢,7)>0.If口and卢a弛linearly

dependent,then

G(口,p,7)=0.

L目m瑚3

Let

G(口,卢,y)bedefined鹪in(8).If口,p∈E

ale

arbitraryandy∈Ewith

I|yl|=1,then

(口,卢)2≤|l口|I2|I卢||2一G(口,p,y).

(10)

Andtheequality

in(10)holdsifandonlyif口,卢andyarelinearlydependent.Theproofs

oflemma2andlemma3havebeensire.inrefel吧nce[4].Hence

theproofsofthem

aIe

omitted.

Weobtainfrom(7)and(8)that

G(口,卢,y)≥(I|a||(卢,y)一II卢||(p,y))2.

(11)As

consequence,itfollowsfrom(10)and(11)that

(口,卢)2≤忆}I2||刚2一r2,

(12)

where

r=||口|I(卢,y)一||p||(口,y).

ProofofTheorem1

letf(t)=∑a.cos(2n一1)t.Thenn=1

f,f∈L2(o,-。y),andf(0)=∑%and

n2l

以詈)=o.According

tothe

relations(6),(9)and(12),wehave

.玉

(∑%)4=4(12s<t)f(t)dt)2=4(厂,厂)2≤4(II

fII

II厂II2一r2),

(13)

where

r=II刘(厂,y)一II厂II(f,y).

Itiseasyto

deduce

that

IIfII

2=J:凡)¨号善口2n

(14)

and

Ill

II::f专(厂(£))2df:7c杰(凡一万1,2%2j

(15)

J0

We锄eh。。眙y:历;.。蝻汕ly,II

tl:(Cy2dt)忱:1.Hence(厂,y):C厂ydt=一瓜∑%

H=l

And(f,y)=j:∥d‘=一瓜∑n=l(一n)2a./(2几一1)・nefef豳weobtain

r=一号(∑%,:一雩(妻%2)it2妻%+雩(壹(n—i1邶2(16)

‘B=11∑口。+等(∑(n—i邶。)忱∑∑哔.n=1=。n=1-

。-22y龙妻生哗.

Iil

n一二

Subsfitufing(14).(15)and(16)in(13)。weobtainaftersomesimplificationsthat

(∑口。)4≤f∑口2。∑n一万1,x2口2。一R2,

(17)

n=1

n=1

n=1

where

R=4r.

Evidently,the

functions以t),厂(t),and7= ̄/2/7c锄linearlyindependent,by

lemma3itisimpossibletotake

theequMity

in(13),i.e.in(17).

Thus

theproofoftheorem1iS

completed.

(下转第33页)

第5期周俊:巨灾指数模型及其衍生品套利定价方法

33

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(上接第26页)

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关于Carlson不等式

石艳平1,尚小舟1,贺乐平2

(1.吉首大学师范学院数学与计算机系,湖南吉首416000;2.吉首大学数学与计算机科学学院,湖南吉首416000)

摘要:利用精化的Cauchy不等式,对I.andau不等式进行了改进.同时,给出了Carlson不等式的一种加强式.关键词:Carlson不等式;landau不等式;内积;范数中图分类号:0178

文献标识码:A

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