什么是不等式【关于Carlson不等式】
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.
8
sharpeningofCauchy’sineqIIali妙.And此
Keywords:Carlsoninequality;Landauinequality;innerproduct;norm
Q£nmnber:0178
I)ocmnent∞de:A
1IntroductionandLet{%}be
a
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
a
lotofresultsoflegance.One0f
tll锄
isLandauinequalityoftheform
器
then
an
。∑Ⅲ
‰
r≤一
。∑删
:%
.妻(凡一{)z%2
rt=1
二
(2)
‘i軎扎扩;岫妇坶
of(2)will
be
=
isthe
妇
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,
2
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
一
^=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∞
口
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
口
)
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
p
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
J
(6)
b
We
nextintroduce
a
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
1
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
a
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
2
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
y
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
1
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
一
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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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
(责任编辑向阳洁)
