概率论与数理统计英文版总结材料docx.docx
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概率论与数理统计英文版总结材料docx
实用标准
SampleSpace样本空间
Thesetofallpossibleoutcomesofastatisticalexperimentiscalledthesample
space.
Event事件
Aneventisasubsetofasamplespace.
certainevent(必然事件):
ThesamplespaceSitself,iscertainlyanevent,whichiscalledacertainevent,
meansthatitalwaysoccursintheexperiment.
impossibleevent(不可能事件):
Theemptyset,denotedby,isalsoanevent,calledanimpossibleevent,
meansthatitneveroccursintheexperiment.
Probabilityofevents(概率)
Ifthenumberofsuccessesinntrailsisdenotedbys,andifthesequenceof
relativefrequenciess/nobtainedforlargerandlargervalueofnapproachesa
limit,thenthislimitisdefinedastheprobabilityofsuccessinasingletrial.
“equallylikelytooccur”------probability(古典概率)
IfasamplespaceSconsistsofNsamplepoints,eachisequallylikelytooccur.
AssumethattheeventAconsistsofnsamplepoints,thentheprobabilityp
thatAoccursis
pP(A)
n
N
Mutuallyexclusive(互斥事件)
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实用标准
Definition2.4.1EventsA1,A2,L,Anarecalledmutuallyexclusive,if
AiIAj,ij.
Theorem2.4.1IfAandBaremutuallyexclusive,then
P(AUB)P(A)P(B)(2.4.1)
Mutuallyindependent事件的独立性
TwoeventsAandBaresaidtobeindependentif
P(AIB)P(A)P(B)
OrTwoeventsAandBareindependentifandonlyif
P(B|A)P(B).
ConditionalProbability条件概率
Theprobabilityofaneventisfrequentlyinfluencedbyotherevents.
DefinitionTheconditionalprobabilityofB,givenA,denotedbyP(B|A),is
definedby
P(AIB)
P(B|A)
P(A)
ifP(A)0.(2.5.1)
Themultiplicationtheorem乘法定理
If
A1,A2,L
Ak
areevents,then
P(A1IA2I
L
Ak)
P(A1)P(A2|A1)P(A3|A1IA2)L
P(Ak|A1I
A2IL
IAk1)
If
the
events
A1,A2,L
Ak
are
independent,
then
for
anysubset
{i1,i2,L,im}
{1,2,L
k},
P(Ai1
IAi2
IL
Aim)
P(Ai1
)P(Ai2
)L
P(Aim)
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实用标准
(全概率公式totalprobability)
Theorem2.6.1.IftheeventsB1,B2,L,Bkconstituteapartitionofthe
samplespaceSsuchthatP(Bj)0forj1,2,L,k,thanforanyevent
AofS,
kk
P(A)P(AIBj)
j1
P(Bj)P(AIBj)
(2.6.2)
j1
(贝叶斯公式Bayes’formula.
)
Theorem2.6.2Ifthe
events
B1,B2,L,Bk
constitute
a
partition
of
the
samplespaceSsuchthat
P(Bj)
0forj1,2,L
k,thanforany
eventAofS,
P(A)0,
P(Bi|A)
P(Bi)P(A|Bi)
.
for
i
1,2,L
k
k
P(Bj)P(A|Bj)
j1
(2.6.2)
ProofBythedefinitionofconditionalprobability,
P(BiIA)
P(Bi|A)
P(A)
Usingthetheoremoftotalprobability,wehave
P(Bi|A)k
P(Bi)P(A|Bi)
i1,2,L,k
P(Bj)P(A|Bj)
j1
1.randomvariabledefinition
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实用标准
Definition3.1.1Arandomvariableisarealvaluedfunction
definedonasamplespace;i.e.itassignsarealnumbertoeachsamplepointinthesamplespace.
2.Distributionfunction
Definition3.1.2LetXbearandomvariableonthesample
spaceS.Thenthefunction
F(X)P(Xx).xR
iscalledthedistributionfunctionofX
NoteThedistributionfunctionF(X)isdefinedonreal
numbers,notonsamplespace.
3.Properties
ThedistributionfunctionF(x)ofarandomvariableXhasthefollowingproperties:
(1)F(x)isnon-decreasing.
Infact,ifx1x2,thentheevent{Xx1}isasubsetofthe
event{Xx2},thus
F(x1)P(Xx1)P(Xx2)F(x2)
(2)F()limF(x)0,
x
F()limF(x)1.
x
(3)Foranyx0R,limF(x)F(x00)F(x0).Thisistosay,the
xx00
distributionfunctionF(x)ofarandomvariableXisright
continuous.
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实用标准
3.2DiscreteRandomVariables
离散型随机量
Definition
3.2.1
A
random
variable
Xiscalled
a
discrete
random
variable
if
ittakes
valuesfrom
afinitesetor,
aset
whoseelementscanbewrittenasasequence
{a1,a2,L
an,L}
geometricdistribution
(几何分布)
X
1
2
3
4
⋯k
⋯
P
p
q1
q2
q3
qk
-
p
p
p
1p
⋯
Binomialdistribution
(二项分布)
Definition
3.4.1
The
number
Xof
successes
in
n
Bernoulli
trialsis
called
a
binomial
random
variable.The
probability
distribution
of
this
discrete
random
variable
is
called
the
binomialdistribution
withparameters
nand
p,denotedby
B(n,p).
poissondistribution
(泊松分布)
Definition
3.5.1
Adiscrete
random
variable
X
is
calleda
Poisson
random
variable,
ifittakes
values
from
the
set
{0,1,2,L},andif
k
P(X
k)
p(k;)
e
0
k
0,1,2,L
k!
(3.5.1)
Distribution(3.5.1)iscalledthePoissondistributionwith
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实用标准
parameter
denotedby
P(
).
Expectation(mean)
数学期望
Definition
3.3.1
Let
X
be
adiscrete
randomvariable.
The
expectation
or
mean
of
X
isdefinedas
E(X)
xP(X
x)
(3.3.1)
x
2.Variance
方差
standarddeviation
(标准差)
Definition3.3.2
Let
X
beadiscreterandomvariable,having
expectation
E(X)
.Thenthevariance
ofX,denoteby
D(X)
isdefinedastheexpectationoftherandomvariable
(X
)2
D(X)
E
(X
)2
(3.3.6)
Thesquarerootofthevariance
D(X),denoteby
D(X),
2
1
iscalledthe
standard
deviation
of
X:
D(X)
EX
2
(3.3.7)
probabilitydensityfunction概率密度函数
Definition4.1.1Afunctionf(x)definedon(,)iscalledaprobability
densityfunction(概率密度函数)if:
(i)f(x)0foranyxR;
(ii)f(x)isintergrable(可积的)on(,)andf(x)dx1.
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实用标准
Definition4.1.2
Letf(x)beaprobabilitydensityfunction.IfXisarandomvariablehaving
distributionfunction
x
F(x)P(Xx)f(t)dt,(4.1.1)
thenXiscalledacontinuousrandomvariablehavingdensityfunctionf(x).Inthis
case,
x2
P(x1Xx2)
f(t)dt.
(4.1.2)
x1
5.Mean(均值)
Definition4.1.2LetXbeacontinuousrandomvariablehavingprobabilitydensityfunctionf(x).Thenthemean(orexpectation)ofXisdefinedby
E(X)xf(x)dx,(4.1.3)
6.variance方差
Similarly,thevarianceandstandarddeviationofacontinuousrandomvariableXis
definedby
2D(X)E((X)2),(4.1.4)
WhereE(X)isthemeanofX,isreferredtoasthestandarddeviation.
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实用标准
Weeasilyget
2
D(X)
x2f(x)dx
2.
(4.1.5)
.
4.2UniformDistribution
均匀分布
Theuniformdistribution,withtheparameters
aand
b,hasprobabilitydensity
function
1
forax
b,
f(x)b
a
0
elsewhere,
4.5ExponentialDistribution指数分布
Definition
4.5.1AcontinuousvariableXhasanexponentialdistributionwithparameter
(
0)
ifitsdensityfunctionisgivenby
1e
x
for
x
0
f(x)
(4.5.1)
0
for
x
0
Theorem4.5.1ThemeanandvarianceofacontinuousrandomvariableXhaving
exponentialdistributionwithparameterisgivenby
E(X),D(X)2.
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实用标准
4.3NormalDistribution正态分布
1.Definition
Theequationofthenormalprobabilitydensity,whosegraphisshowninFigure
4.3.1,is
f(x)
1
e(x)2/22
x
2
4.4NormalApproximationtotheBinomialDistribution(二
项分布)
X~B(n,p),nislarge(n>30),piscloseto0.50,
X~B(n,p)N(np,npq)
4.7Chebyshev’sTheorem(切比雪夫定理)
Theorem4.7.1Ifaprobabilitydistributionhasmeanμandstandarddeviationσ,
theprobabilityofgettingavaluewhichdeviatesfromμbyatleastkσisatmost
1
k2.Symbolically,
P(|X
|
k)
1
k2.
Jointprobabilitydistribution
(联合分布)
In
thestudy
ofprobability,
givenatleasttworandom
variablesX,Y,...,thataredefinedonaprobabilityspace,the
joint
probability
distribution
for
X,Y,...isaprobability
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实用标准
distributionthatgivestheprobabilitythateachofX,Y,...fallsinanyparticularrangeordiscretesetofvaluesspecifiedforthatvariable.
5.2Conditionaldistribution条件分布
Consistentwiththedefinitionofconditionalprobabilityof
eventswhenAistheeventX=xandBistheeventY=y,the
conditionalprobabilitydistributionofXgivenY=yisdefined
as
pX(x|y)
p(x,y)forallxprovided
pY(y)
pY(y)0.
5.3Statisticalindependent随机变量的独立性
Definition5.3.1Supposethepair{X,Y}ofrealrandomvariableshasjointdistributionfunctionF(x,y).IftheF(x,y)obeytheproductrule
F(x,y)FX(x)FY(y)forallx,y.
thetworandomvariablesXandYareindependent,orthepair{X,Y}isindependent.
5.4CovarianceandCorrelation协方差和相关系数
Wenowdefinetworelatedquantitieswhoserolein
characterizingtheinterdependenceofXandYwewantto
examine.
Definition5.4.1SupposeXandYarerandomvariables.Thecovarianceofthepair{X,Y}is
Cov(X,Y)E[(XX)(YY)].
Thecorrelationcoefficientofthepair{X,Y}is