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应用数学 MATHEMATICA APPLICATA 2002.15{2):if7~12O Approximation of a Solution for a K-Positive Definite Operator Equation in Real Separable Banach Spaces BAI Chuan—zhi( ̄传志) (D pt.of Mathematics,Nanjing Normal University,Nanjing Jiangsu 210097,China) Abstract:Let E be a real separable Banach space with a str ct y COnVeX dual and let A:D(A) E— E be a K-positive definite operator Let f∈E be arbitrary A DeW iterative process with errors is constructed wh ch co rge5 strong1y to the unique solution of the equation A =f Our work ex. tends some oi the known results in[1 3-4]. Keywords:Separahie Banaeh space;K positive definite operator;Iterative process with errors CLC Nutuber:O1 77 Doeumerit code:A AMS(2000)Subject Classification:47A50 Article ID:1001-9847(2002)02—0117—04 Let E be real Banach s口ace with a dual space E ,and let J:E—}2 ‘be the normalized duality mapping defined for each ∈E by J( )一(, ∈E :{ ,f )一I Iz 一II f II。), (1) where<.,.)Ls the general[zed duality pairing.It is well known that if E Ls strictly con vex,then J is singly valued.In the sequel we shall denote single valued duality mapping by J. Let E be a separab1e Banach space and lel El be a dense subspace of E.An operator A with domainD(A) E1 is called continuously E1 invertible if the range ofA,R(A),withA con dered as an o口erator restrictedtoELis denseinEandA has a boundedinverse onR(A). Denniti0n 1 Let E be a real Banach space and let A be a linear unbounded operator de fined。n a dense domain D(A),in E.The operator A is called a K—positive definite(Kpd)if there e xIst a c。n【inuoosly D(A)一inverdble closed linear operator K with D(A) D(K),and a constant c>0 such that forJ(Ku)∈7(Ku), Received date:December 26.2001 m0graphy:BAI Chuan-zhi(1964一).Ⅱ】ale.Han,ph.。student of Nanjing Normal Universi y‘Maj。 一 search fleldsare nonlinear functional analysis and nonlinear different equation・ 维普资讯 http://www.cqvip.com
118 MATHEMATICA APPLlCATA 2002 <Au,j(Ku)>≥c Ku l ,“∈D(A). (2) Without los of genera[hy,we may assume f∈(0,1). In[1],Chidume and Aneke proved the following theorem which is the extension of the corresponding result of Petryshyn E23. "rh ̄rem CAe :Let E be a real separable Banach space with a strictly convex dual E’ andletA be aKpd operator withD(A)一D(K).Suppose(Ax, (Ky))一(Kx,J(Ay)>, V , ∈D(A).Thenthere exists a constant >0 suchthatfor all ∈D(A), ll儿c ll≤a l lKx l1. (3) Furthermore,the operatorAis closed,R(A)一E,andthe equationAx—f,for eachf∈E, has a unique solution. In the sequel we need the following lemma. Lemma 2嘲Let , ,and be nonnegative real sequences satisfying the following in equality: ≤(1一口 ) + 一o,,,n一0,l,2,…, (4) where ∈E0,1],∑ 。Ⅱn=。。, =。( ),and∑ 。 <oo.Then —,0 as n—,oo. We observethatinequality(2)is equivalenttothefollowing one:<Au—cKu,J(Ku)>≥ 0,and it follows from[Lemma 1.1 of Kato,6]that l1 Ku ≤ Ku+s(Au—cKu)0,V“∈D(A)and V s>0. (5) We now prove the following: Theorem 3 Let E be a real separable Banach space with a strictly convex dual and let A :D(A) E—+ be a Kpd—operator with D(A)一D(K).Suppoe(Ax, (Ky)>=(Kx, , r 、for all z.Y∈D(A).For arbitrary f∈E,and errors sequences{ ),{E )c D(A). Then Deftne the sequence{z ) o iteratively from an arbitrary z0∈D(A)by z叶】一 + + ,n≥0; —K~f—K~Ay ,n≥0; … =z + 一E ,n≥0; =K~f—K~Ax ,n≥0; 0≤“≤ ,0≤“≤ 口 +c2(1一c)’ n≥0{ (7) ∑£ =。。,and∑(I IAe II+II AE II)<。。, (8) n=C 一0 where is the constant appearing in inequality(2),c∈(0,1)is the constant appearing in in— equality(3).Then{z ) 。converges strongly to the unique solution of the equation A 一,. Proof The existence of a unqiue solution to the equation Ax=,follows from Theorem CA.Using Eqs.(6),and the linearity of A and K we obtain K 】一Ky 一 ^ 一Ae.,,Ky 一K ~ A 一Aa . (9) K 一Ky一 .,A +Ae 一(1+5..)Ky +s (Ay 一cKY 一 KY 一5 (AY 一cKy..)一 TAe 一(1+s )(蝌 + 睾i(A7 一cKY”)) 一s (1一c)K7 一 (AT 一A )+AE . Since ll Ax l1≤ l1 Kx ll,Vz∈D(A),from(9).we obtain 维普资讯 http://www.cqvip.com
No.2 BA1 Chuan-zhi:Approximation of a Solution for a Operator Equation ll9 llA7 ~ nll≤口JJK( 一 )¨ =a l} By(5),We have 十AE ≤a l J脚 l}十a l lAE lI. l脚 ≥(1十 》埘 十惫(肿 一 y )I 一 (1一c)}1 Ky 一 Ay 一A ll一 AE l l≥(1十 )Jf 一J一 (1一f)JJ Ky 一口。《JJ K,u JJ一(1+甜 ) Ae jJ 一(1+∞ )lI AE l1. (1十 )l_Ky 一 5 Thls llK7 0≤箨警11脚 1l+ l【A£ .simi1arly.by(9),we。bta.nthat l≤ 【lKy + .Fmm(7) |sefdsyt。checklhat 。< 。< we obtain ≤ , Ⅲ< ≤ 十詈, ≤ + . ≤ ≤错 + llAE + ≤(1一c(1一c) )0 0十(1十詈) 血 l1十(1十 ≤(1一c(1一c)t )ll K 0+h(『『A£ ll十l lAe ), where h= max)ll l l(1o) {1+},1十 0 as .N。w set 一J】 ll, =c(1-c) ,疋=o, and以一h(1I血 +}1 }1).Then(i0)yields P一】≤(1一 ) + .From(8),we have ∈[o,13,∑ 。 :。。,and∑二。 <oo.ByLemma 2,We asserttha —-0 as — oo, i.e.,l1脚 l l∞.Since K is continuously D(A)一invertible,there exists >0 ,V 28∈D(K).This inequality yieldsthat 0 as 一。。,i.e., A~f,the unique solu— such that 0 Ka"}1≥卢Il tion ofAx=。 一f as n oo.Since A has a bounded inverse,this implies Corollary 4 Let E be a real separable Banach space with a strictly convex dual and let A :D(A) E— E be a Kpd-operator with D(A)一D(K).Supp0e<Ax, (Ky))=(Kx, j(Ay))for all .Y∈D(A).For arbitrary f∈E.Define the sequence{ } c iteratiely from an arbitrary o∈D(A)by z 】=Y 十 y ,n>1-0, =(11) K_。,一K~Ay , ≥0 Y— 十 :, ≥0, K~f—K~Az ,n≥0. 。≤ ≤ ,o≤ ≤ , ≥o,and 一。。, (12) 维普资讯 http://www.cqvip.com
120 MATHEMATICA APPLICATA where d is the constant appearing in inequality(2),c∈(O,1)is the constant appearing in in equality(3).Then{ ..) c converges strongly tO the unique solution of the equationm=, Proof Net =E =口(the zero element ofE)for all ≥0 in Theorem 3.Then the con— clusion of Corollary 4 follows from Theorem 3. Remark 5 It iS well known that E iS a real uniformly smooth Banach space implies E is a real Banach space with a strictly convex dua1.Conversely,it is not holds.Noting that the condition(12)here is weaker than the conditions(10)一(13)in E41.so Corollary 4 extend the corresponding results in E41 and the corresponding results in 1,3]. References: [1]Chidume c E.Aneke S J.Existence.uniqueness and approximation ol a solution for a K-positive deft— nite operator equation[J].App1.Ana1.1993.50:285~294. 823 Petryshyn W V.Direct and iterathre methods for the solution of linear operator equations in Hilbert spaces[J]Trans.Amer.Math.Soc.1962,105:136~1 75. [3]Chidume C E,Osilike M O.Approximation of a solution for a K-positive deifmte operator equationrJ]. J.Math.A口a1.App1.1997-210:i~7. [43 Bai Chuanzh[.Approximation of a solution for K-positive definite operator equation in uniofrmly smooth separable Banach spaces[J].J.Math.Ana1.App1.1999.236:236~242. [5]L[u L S.1shikawa and Mann iterative process with errors for nonlinear strongly accretive mappings in Banach spaces[J]J.Math.Ana1.App1.1995.194:1 14~125. [63 Kato T.Nonlinear semigroups and evolution equations[J].J.Math.Soe.Japan.19 64t19:508~520. 实可分Banach空间中K正定算子方程的逼近解 柏传志 (南京师范大学数学系,江苏南京210097) 摘要:设E是带严格凸对偶空间的实可分Banach空间,设A:D(A) E—E是一K正定 算子.对任意,∈E,我们构造了强收敛于算子方程Ar—f唯一解的新的带误差的迭代过程. 我们的工作推广了文[1,3—4]中的结果. 关键词:可分Banach空问}K正定算子;带误差的迭代过程