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A NOTE ON THE DISTRIBUTION OF THE TIME OF THE FIRST k-RECORD

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1998年度日本オペレーションズ。リサーチ学会 春季研究発表会

て −A−11

ANOTEONTHEDISTRIBUT王ONOF

TⅢETIMEOFTHEF量RSTk・RECORD

O1303783 愛知大学 玉置光司 TAMAKIMitsushi

Weexplicitlygivetheprobabilitymassfunctionandtheprobabilitygenemtingfunctionofthe firstk−TeCOrdindexfbrasequenceofimdependencamdidenticallydistributedmndomvariablesthat takeonamnitesetorpossiblevalues.Wealsocomputeits払ctorialmoments. 且。‡N甘監ODUCT五⑬NÅND$冊ヱ岨ÅRV LetXl,X2,…beindependentandidenticallydistFibuted汽mite−Valuedrandomvariableswith probabilitymassfunctiom pi=P(Ⅹ=i.),i=1,…,m. ForamxedposltlVeintegerk,k>1,血erandomvariable

T=min(n‥Ⅹn≦Ⅹifbrexacdykofthevaluesi,・i=1,...,n)

iscalledtbe汽ー鈍かrgc(〉rd加dβ∬.

AdleTandRoss[1】deteTminedぬemrsttwomo甲entSOfTviaaTeCurSiveformulafbrits

PrObabilitygeneratlngfuncc且OmObmi皿edbyconditionlngOnarandomvariableTj,Whichisdenned

asthe鮎stk−reCOrdindexwhentheobservedraLmdomvariableshaveprobabilitymassfunction

P(Ⅹ=i)= 且〒J,・・・,m・ 巧+…+pm’ Inぬ五s皿Ote,WedeFivechep釘Obabil五電ymassfunctionandtheprobabilicygeneratingfunctionofT expl丘c加Iya皿d也emdetermineitsねc伍Oridmoments. THEOREM 且JeCai=pi+・・・+pm,i=1,…,m.ThendlepTObabilitymassfuncciono[Tis騨Venby

二1(且一軒k,m≧k・

叩=n}=霊pi(芸糎 i=1

MoTeOVer血ep刑)bab血ygeneratimgfunc紅ionP(S)=鴎T]isgivenby

(且) P(S)=墓pi可 王ト1 叫S (2)

LetPj(S)=蜂用j=且,‥.,m.ThenAdlerandRoss軋Theoreml]givearecursive

野鼠⑬⑬厨 ねmula

岬=賢叫1一紳減封j=1,…副

W払五ch,COmbinedwithPm(S)=Sk,Canbeeasilysolvedtoyield −24− © 日本オペレーションズ・リサーチ学会. 無断複写・複製・転載を禁ず.

(2)

巧(S)=姜 lヨ k−1 叫S Thus,Sinceal=1,Wehave m P(S)=Pl(s)=∑ i=1 l r ︵ S p 叫S 彗 l ︵ ︼ l k−1 叫S denotestheprobabilitygeneratlng Whichyields(2).(1)isimmediatefrom(2),because 1−(1一句)s

functionofthenegativebinomialrandomvariablewithparametersk−1andai・andhencecanbe

expandedinto 00 )k ̄1=主(:二紳1(1−納n ̄1・ 叫S Thustheproofiscomplete・ ThefbllowlngCOrOllaryglVeSthefactorialmomentsofT・ COROLLARY Forj=0,1,2,‥・,

恥−1)(叫2)‥・(T−1)】菓閉脚‥樹 ・.i=1

PROOF Fbrj=0,1,2,…,Wehavefrorn(1)that 可(Tl」−1)(T+j−2)…(T−1)】 00 =∑(n・k十j−1)(n・ktj−2)・・・(n・k−1)P(T=n・k) n=0 (kJj−1)(k+j−2)…(k−1) (k+j−1)(k+j−2)…(k−1)

(m+伸一げ)

1 〈 00 ∑ n=0

m∑忠∑畠

p純k− pi中一1町(k十j),

whichisthedesiredresult.ThelastequalityfbllowsfromthewellkLlOWnidentity(See,e・g・,

Ross【2】,p・153)

)n=a叫触・叫≧1・

00 計+㌣ ̄1ト Re鮎remces

l.Adler,I.,&Ross,S.M.(1997).Distributionofthetimeofthefirstk−reCOrd・Probabilityin

血肋g血eer血gα〝dJゆmαfわ朋J放ね〝Ce∫11:273−278・

2.Ross,S.M.(1997).LniTVductiontoprobabilitymOdels,6thed・NewYork:AcademicPress・

3.Tamaki,M.(1998).Anoteonthedistributionofthetimeofthefirstk−reCOrd・Probabilityin

血助g血ee血gd〃dJゆmα血乃αJ∫cfe〝Ce∫12(toap匹ar)・ ー25− © 日本オペレーションズ・リサーチ学会. 無断複写・複製・転載を禁ず.

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