Hindawi Publishing Corporation Abstract and Applied Analysis Volume 2014, Article ID 795016, 7 pages http://dx.doi.org/10.1155/2014/795016
Research Article The Tensor Product Representation of Polynomials of Weak Type in a DF-Space
Masaru Nishihara1 and Kwang Ho Shon2
1 Department of Computer Science and Engineering, Faculty of Information Engineering, Fukuoka Institute of Technology, Fukuoka 811-0295, Japan 2 Department of Mathematics, College of Natural Sciences, Pusan National University, Busan 609-735, Republic of Korea
Correspondence should be addressed to Kwang Ho Shon; [email protected]
Received 15 December 2013; Accepted 19 February 2014; Published 27 March 2014
Academic Editor: Zong-Xuan Chen
Copyright Β© 2014 M. Nishihara and K. H. Shon. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
π Let πΈ and πΉ be locally convex spaces over C and let π( πΈ; πΉ) be the space of all continuous π-homogeneous polynomials from πΈ to πΉ.Wedenotebyβ¨π,π ,ππΈ the π-fold symmetric tensor product space of πΈ endowed with the projective topology. Then, it is well π known that each polynomial πβπ(πΈ; πΉ) is represented as an element in the space πΏ(β¨π,π ,ππΈ; πΉ) of all continuous linear mappings π from β¨π,π ,ππΈ to πΉ. A polynomial πβπ(πΈ; πΉ) is said to be of weak type if, for every bounded set π΅ of πΈ, π|π΅ is weakly continuous π on π΅.Wedenotebyππ€( πΈ; πΉ) the space of all π-homogeneous polynomials of weak type from πΈ to πΉ. In this paper, in case that πΈ π is a DF space, we will give the tensor product representation of the space ππ€( πΈ; .πΉ)
1. Notations and Preliminaries by B(πΈ) thefamilyofallboundedsubsetsofπΈ. We denote by σΈ ββπ΅ the seminorm on πΈ defined by In this section, we collect some notations, some definitions, σ΅© σ΅© σ΅¨ σ΅¨ σ΅©π₯σΈ σ΅© = {σ΅¨β¨π₯, π₯σΈ β©σ΅¨ ;π₯βπ΅}, and some basic properties of locally convex spaces which we σ΅© σ΅©π΅ sup σ΅¨ σ΅¨ (3) use throughout this paper. σΈ Let πΈ1 and πΈ2 be complex vector spaces. Then the pair for every π΅βB(πΈ).Thestrong topology on πΈ is the topology σΈ β¨πΈ1,πΈ2β© is called a dual pair if there exists a bilinear form: on πΈ defined by the set of seminorms {β βπ΅;π΅ β B(πΈ)} on σΈ σΈ σΈ πΈ . Wedenote by πΈπ½ the locally convex space πΈ endowed with (π₯1,π₯2) σ³¨β β¨π₯1,π₯2β©((π₯1,π₯2) βπΈ1 ΓπΈ2) σΈ σΈ σΈ (1) the strong topology. We denote by πΈ the dual space of πΈπ½.Let π΄ be a subset of πΈ. We denote by π΄ the topological closure of satisfying the following conditions: σΈ σΈ σΈ σΈ σΈ the subset π΄ of πΈβπΈ for the topology π(πΈ ,πΈ ).Thepolar π΄β π΄ (1) If β¨π₯1,π₯2β©=0for every π₯2 βπΈ2, π₯1 =0. set of is defined by
(2) If β¨π₯1,π₯2β©=0for every π₯1 βπΈ1, π₯2 =0. σ΅¨ σ΅¨ β σΈ σΈ σ΅¨ σΈ σ΅¨ π΄ ={π₯ βπΈ; sup σ΅¨β¨π₯, π₯ β©σ΅¨ β€1}. (4) π₯βπ΄ We denote by π(πΈ1,πΈ2) (resp., π(πΈ2,πΈ1))thetopologyonπΈ1 πΈ ββ (resp., 2) defined by the subset of seminorms: We denote by π΄ the bipolar set of π΄ for the dual pair σΈ σΈ σΈ σΈ σ΅¨ σ΅¨ σ΅¨ σ΅¨ β¨πΈ ,πΈ β©.Asubsetπ of πΈ is said to be equicontinuous if there {σ΅¨β¨β , π₯2β©σ΅¨ ;π₯2 βπΈ2}(resp.{σ΅¨β¨π₯1,β β©σ΅¨ ;π₯1 βπΈ1}) . β σ΅¨ σ΅¨ σ΅¨ σ΅¨ (2) exists a neighborhood π of 0 in πΈ such that πβπ. πΈ ππ (πΈ) Let be a locally convex space. We denote by the set Lemma 1. Let π beaboundedsubsetofalocallyconvexspace of all nontrivial continuous seminorms on πΈ.Thetopology σΈ πΈ. Then the following statements hold: π(πΈ, πΈ ) on πΈ is called the weak topology of πΈ and the topology σΈ σΈ β σΈ ββ π(πΈ ,πΈ)on πΈ is called the weak topology of πΈ . We denote (1) π=π if π is absolutely convex. 2 Abstract and Applied Analysis
σΈ σΈ σΈ (2) π is compact with the topology π(πΈ ,πΈ ). 2. The Extension of Polynomial Mappings of σΈ σΈ Weak Type (3) πΈ = βπβB(πΈ) π. σΈ σΈ In this section, we will give basic properties of polynomial (4) Let π΄ be an equicontinuous subset of πΈ for the dual σΈ σΈ σΈ mappings on locally convex spaces and discuss the extension pair β¨πΈ ,πΈ β©. Then there exists an absolutely convex ββ of weak type on locally convex spaces. For more detailed bounded subset π of πΈ,suchthatπ΄βπ . properties of polynomials on locally convex spaces, see πΈ πΉ (1) πβπββ πββ π(πΈσΈ σΈ ,πΈσΈ ) πβ Dineen [1, 2]andMujica[3]. Let and be locally convex Proof. Since and is -closed, π πΏ (ππΈ; πΉ) πββ πββ β π π₯σΈ σΈ β π spaces and let be a positive integer. We denote by π .Weshallshow . We assume that 0 . π πΈπ σΈ σΈ σΈ σΈ the space of all -linear mappings from the product space πΈ σΈ σΈ σΈ πΈ π We denote by π(πΈ ,πΈ ) the locally convex space endowed of π-copies of πΈ into πΉ and denote by πΏππ€( πΈ; πΉ) the space σΈ σΈ σΈ σΈ σΈ σΈ σΈ σΈ with the topology π(πΈ ,πΈ ).Since(πΈπ(πΈσΈ σΈ ,πΈσΈ )) =πΈand of all π-linear mappings, which are π(πΈ, πΈ )-continuous on σΈ σΈ σΈ πΈπ πΈπ πΉ π is π(πΈ ,πΈ )-closed absolutely convex, by Hahn-Banach bounded subsets of ,fromtheproductspace into .A σΈ σΈ π:πΈ βπΉ π theorem there exists π₯ βπΈ such that mapping is called an -homogeneous polynomial from πΈ into πΉ if there exists an π-linear mapping π’ from πΈ σ΅¨ σ΅¨ σ΅¨ σΈ σΈ σΈ σ΅¨ into πΉ such that sup σ΅¨β¨π₯ ,π₯ β©σ΅¨ β€1, π₯σΈ σΈ βπ (5) π (π₯) =π’(π₯,...,π₯) , (8) σ΅¨ σ΅¨ σ΅¨β¨π₯σΈ σΈ ,π₯σΈ β©σ΅¨ >1. σ΅¨ 0 σ΅¨ for every π₯βπΈ.Ifπ is an π-homogeneous polynomial from πΈ into πΉ, there exists uniquely a symmetric π-linear σΈ β σΈ σΈ ββ π’ π (ππΈ; πΉ) π Thus, it is valid that π₯ β π and π₯0 β π .Thuswehave mapping . We denote by π the space of all - ββ ββ ββ ββ homogeneous polynomials from πΈ into πΉ. We denote by π β π.Sinceπ β π , π β π.Hence,wehaveπ= π π ββ π( πΈ; πΉ) (resp., πΏ( πΈ; )thespaceofallcontinuousπΉ) π- π . σΈ σΈ σΈ homogeneous polynomials from πΈ (resp., all continuous π- (2) We denote by Ξ(π) the π(πΈ ,πΈ )-closed absolutely π π linear mappings from πΈ )intoπΉ. We denote by πππ€( πΈ; πΉ) convex hull of the set π. By the statement (1) we have σΈ the space of all π(πΈ, πΈ )-continuous polynomials on each πΈ Ξ (π) =πββ. bounded subset of .Weset (6) π π π ππ€ ( πΈ; πΉ) =π( πΈ; πΉ)ππ€ β©π ( πΈ; πΉ) , β (9) The polar set π is an absolutely convex neighborhood of 0 π π π σΈ σΈ σΈ σΈ πΏπ€ ( πΈ; πΉ) =πΏ( πΈ; πΉ) β©πΏππ€ ( πΈ; πΉ) . in πΈπ½. Therefore, Ξ(π) is a π(πΈ ,πΈ )-closed equicontinuous σΈ σΈ σΈ σΈ σΈ π subset of πΈ . By Banach-Alaoglu theorem, Ξ(π) is π(πΈ ,πΈ )- A polynomial belonging to ππ€( πΈ; πΉ) is said to be of weak σΈ σΈ σΈ compact. Since πβΞ(π), π is also π(πΈ ,πΈ )-compact. type. σΈ σΈ (3) It is clear that βπβB(πΈ) πβπΈ .Weshallshowthat σΈ σΈ σΈ σΈ σΈ σΈ Lemma 2. Let πΈ and πΉ be locally convex spaces and let π’ be πΈ ββ π.Letπ₯ be a point of πΈ . Then, there exists π πβB(πΈ) an π-linear mapping belonging to πΏπ€( πΈ; .LetπΉ) π΄1,...,π΄π be π 0 πΈσΈ |β¨π₯, π₯σΈ σΈ β©| β€ 1 an open neighborhood of in π½ such that absolutely convex bounded subsets of πΈ.Letππ be any point of σΈ σΈ σΈ σΈ for every π₯βπ. By the definition of the space πΈπ½ there exists π(πΈ ,πΈ )-closure π΄π of π΄π for each π with 2β€πβ€π.Wedenote σΈ σΈ σΈ σΈ σΈ an absolutely convex bounded subset πβB(πΈ) such that by Nπ€β (πΈ )(0) the system of all π(πΈ ,πΈ )-neighborhoods of 0 β σΈ σΈ σΈ σΈ π βπ. Thus, by the statement (1) we have in πΈ .Then,foranyπΌ β ππ (πΉ) there exists πβNπ€β (πΈ )(0) such that σΈ σΈ β ββ π₯ βπ βπ = π. (7) πΌ(π’(π₯1,...,π₯π)) < 1, (10)
σΈ σΈ for every (π₯1,...,π₯π) β (πβ©π΄1)Γ((π2 +π)β©π΄2)Γβ β β Γ((ππ + Thus, we have πΈ =βπβB(πΈ) π. σΈ σΈ π) β© π΄π). (4) Since π΄ is an equicontinuous subset of πΈ , there exists π 0 πΈσΈ π΄βπβ π a neighborhood of in π½ such that .Since is a Proof. Weshallprovethislemmabyinductiononπ.Letπ= 0 πΈσΈ neighborhood of in π½, there exists an absolutely convex 1. Then, the conclusion of this lemma is true since 0βπ΄1 β σΈ σΈ σΈ σΈ bounded subset π of πΈ such that π βπ.Thus,wehave and π(πΈ, πΈ ) is the induced topology of the topology π(πΈ ,πΈ ) β ββ π΄βπ βπ .Thiscompletestheproof. onto πΈ. We suppose that the conclusion of this lemma is true for πβ1 all mappings belonging to πΏπ€( πΈ; .πΉ) And we assume that AfilterF ={πΉπΌ} of a locally convex space πΈ is called a π for π’βπΏπ€( πΈ; ,πΉ) the conclusion is not true. Then, there Cauchy filter if for every neighborhood π of 0 there exists an σΈ σΈ exists πΌ β ππ (πΉ) such that for every πβNπ€β (πΈ )(0) there πΉβF such that {π₯βπ¦;π₯,π¦βπΉ}βπ. A locally convex space is a point: πΈ is said to be complete if any Cauchy filter on πΈ converges to πΈ a point of . There exists the smallest complete locally convex (π₯1π,π₯2π,...,π₯ππ)β(πβ©π΄1)Γ((π2 +π)β©π΄2) space πΈΜ containing πΈ as a subspace. The locally convex space (11) Γβ β β Γ((π +π)β©π΄ ), πΈΜ is called the completion of πΈ. π π Abstract and Applied Analysis 3
satisfying for every (π§1,π§3 ...,π§π) β (π(πβ1)β©π΄1)Γ((π3 +π(πβ1))β© π΄3) Γ β β β Γ ((ππ +π(πβ1))β©π΄π).Thenwehave πΌ (π’ (π₯1π,π₯2π,...,π₯ππ)) β₯1. (12) πΌ(π’(π₯1π(πβ1),π₯2π(πβ1) βπ₯2π(πβ2),...,π₯πβ1π(πβ1) σΈ Since π’ is π(πΈ, πΈ )-continuous at (0,0,...,0) on each βπ₯ ,π₯ βπ₯ )) π σΈ πβ1π(1) ππ(πβ1) ππ absolutely convex bounded subset of πΈ and π(πΈ, πΈ ) is the σΈ σΈ σΈ induced topology of π(πΈ ,πΈ ) onto πΈ, there exists πβ β₯πΌ(π’(π₯1π(πβ1),π₯2π(πβ1),...,π₯ππ(πβ1))) σΈ σΈ Nπ€β (πΈ )(0) such that (21) β β πΌ(π’(π₯ ,π₯ ,...,π₯ )) 1π(πβ1) 2π(π2) ππ(ππ) 1 (π )βπΎ πΌ (π’ (π₯ ,π₯ ,...,π₯ )) β€ π 1 2 π 4 (13) 1 1 β₯1β(2πβ1 β1)Γ β₯ , 2π 2 for every π₯π β2(πβ©π΄π) with 1β€πβ€π.Wechoosea decreasing sequence π β π(1) β π(2) β β β β β π(πβ1) σΈ σΈ where πΎ={(π2,...,ππ); ππ β{πβ1,πβπ},π=2,...,π}\{(πβ of elements of Nπ€β(πΈ )(0) by the process of (π β 1) steps as 1,...,πβ1)}and π(0) = π. follows. If we set At the first step, we consider the (π β 1)-linear mapping: (π¦1,π¦2,...,π¦π)= (π₯1π(πβ1),π₯2π(πβ1) βπ₯2π(πβ2),..., (π§1,...,π§πβ1) σ³¨β π’ (π§1,...,π§πβ1,π₯ππ) , (14) (22) π₯ππ(πβ1) βπ₯ππ), πβ1 belonging to πΏπ€( πΈ; .πΉ) By the assumption of induction, σΈ σΈ we have there exists π(1) β Nπ€β (πΈ )(0) with π(1) β π such that 1 πΌ(π’(π¦ ,...,π¦ )) β₯ , 1 1 π πΌ(π’(π§ ,...,π§ ,π₯ )) β€ 2 1 πβ1 ππ π (15) 2 (23) (π¦1,π¦2,...,π¦π)β (πβ©π΄1)Γ{2(πβ©π΄2)} for every (π§1,...,π§πβ1) β (π(1) β© π΄1) Γ ((π2 + π(1)) β© π΄2)Γ Γβ β β Γ{2(πβ©π΄π)} . β β β Γ ((ππβ1 + π(1)) β© π΄πβ1). (πβ1) Atthesecondstep,weconsiderthe -linear mapping This is a contradiction by13 ( ). This completes the proof.
(π§1,...,π§πβ2,π§π) σ³¨β π’ (π§1,...,π§πβ2,π₯πβ1π(1),π§π) (16) Lemma 3. Let πΈ be a locally convex space, let πΉ be a complete πβ1 π’ π belonging to πΏπ€( πΈ; .πΉ) By the assumption of induction, locally convex space and let be an -linear mapping belonging σΈ σΈ πΏ (ππΈ; πΉ) π΄ ,...,π΄ there exists π(2) β Nπ€β (πΈ )(0) with π(2) β π(1) such to π€ .Let 1 π be absolutely convex bounded πΈ π(πΈσΈ σΈ ,πΈσΈ ) that subsets of . Then there exists a -continuous mapping π’Μπ΄ Γβ β β Γπ΄ from π΄1 Γβ β β Γπ΄π into πΉ such that π’Μπ΄ Γβ β β Γπ΄ =π’on 1 π΄ 1 Γβ β β Γπ΄π 1 π πΌ(π’(π§ ,...,π§ ,π₯ ,π§ )) β€ 1 π. 1 πβ2 πβ1π(1) π 2π (17) σΈ σΈ σΈ Proof. Let ππ be any point of the π(πΈ ,πΈ )-closure π΄π of π΄π for for every point (π§1,...,π§πβ2,π§π) of each π with 1β€πβ€π. At first, we shall show that a filter of πΉ F (π ,...,π )= {π’((π +π)β©π΄ ,...,(π +π)β©π΄ ); (π (2) β©π΄1)Γ((π2 +π(2))β©π΄2) 1 π 1 1 π π σΈ σΈ Γβ β β Γ((ππβ2 +π(2))β©π΄πβ2) Γ ((ππ +π(2))β©π΄π). πβNπ€β (πΈ ) (0)} (18) (24) Repeating this process, at the (π β 1)th step, we consider (π β 1) is a Cauchy filter. Let πΌ be an arbitrary continuous seminorm the -linear mapping: σΈ σΈ of πΉ.ByLemma 2 there exists πβNπ€β (πΈ )(0) such that (π§ ,π§ ,...,π§ )σ³¨βπ’(π§,π₯ ,π§ ,...,π§ ), 1 3 π 1 2π(πβ2) 3 π (19) 1 πΌ (π’ (π₯1,π₯2,...,π₯π)) < , (25) πβ1 π belonging to πΏπ€( πΈ; .πΉ) By the assumption of induction, σΈ σΈ there exists π(πβ1) β Nπ€β (πΈ )(0) with π(πβ1) β π(πβ2) for every point (π₯1,π₯2,...,π₯π) of such that π π 1 β (β ((πΎ π +2π)β©2π΄ )) , πΌ(π’(π§ ,π₯ ,π§ ,...,π§ )) β€ ππ π π (26) 1 2π(πβ2) 3 π 2π (20) π=1 π=1 4 Abstract and Applied Analysis
π σΈ σΈ σΈ σΈ σΈ where πΎππ =1(π=π)ΜΈ and πΎππ = 0 (π = π).Then,wehave (3) There exists πβπΜ π( πΈ ;πΉ)such that πΜ is π(πΈ ,πΈ )- σΈ σΈ continuous on each equicontinuous subset of πΈ and πΌ(π’(π₯1,π₯2,...,π₯π)βπ’(π¦1,π¦2,...,π¦π)) π|πΈ=πΜ . π β€ πΌ (π’1 (π₯ βπ¦1,π₯2,...,π₯π)) (4) is weakly uniformly continuous on every bounded subset of πΈ. +πΌ(π’(π¦1,π₯2 βπ¦2,π₯3,...,π₯π)) Proof. We shall show that (1) implies (3). There exists a (27) π +πΌ(π’(π¦1,π¦2,π₯3 βπ¦3,π₯4,...,π₯π)) symmetric π-linear mapping π’ from πΈ into πΉ such that π(π₯) = π’(π₯,...,π₯) for every π₯βπΈ.Bythepolarization +β β β +πΌ(π’(π¦,π¦ ,...,π¦ ,π₯ βπ¦ )) π 1 2 πβ1 π π formula, we have π’βπΏπ€( πΈ, .ByπΉ) Lemma 4 there exists π’βπΏΜ (ππΈσΈ σΈ ;πΉ) π’|πΈΜ π =π’ π’Μ π(πΈσΈ σΈ ,πΈσΈ ) 1 π with such that is - β€πΓ =1, continuous on π΄1 Γβ β β Γπ΄π for all absolutely convex bounded π π σΈ σΈ subsets π΄1,...,π΄π of πΈ.WedefineπβπΜ π( πΈ ;πΉ)by π(π₯)Μ = π π’(π₯,...,π₯)Μ π₯βπΈσΈ σΈ πΜ for every (π₯1,...,π₯π), (π¦1,...,π¦π)ββπ=1((ππ +π)β©π΄π).Thus, for every .ByLemma 1, satisfies all (3) the filter F(π1,...,ππ) is a Cauchy filter. Since πΉ is complete required conditions of the statement . ββ and Hausdorff, there exists uniquely the limit point of the (3) implies (2) since π is equicontinuous for every filter F(π1,...,ππ) for every (π1,...,ππ)βπ΄1 Γβ β β Γπ΄π. absolutely convex bounded subset π of πΈ. π’Μ (π ,...,π ) We shall show that (2) implies (4).Letπ΄ be a bounded We denote by π΄1Γβ β β Γπ΄π 1 π the limit point of the filter subset of πΈ. We denote by π theabsolutelyconvexhull F(π1,...,ππ) for every (π1,...,ππ)βπ΄1 Γ β β β Γ π΄π.Then σΈ σΈ σΈ of π΄ in πΈ.Then,π is a bounded subset of πΈ,andπ΄β π’Μπ΄ Γβ β β Γπ΄ defines π(πΈ ,πΈ )-continuous mapping from π΄1 Γ σΈ σΈ σΈ 1 π π.Bystatement(2), there exists a π(πΈ ,πΈ )-continuous β β β Γπ΄π into πΉ with Μ Μ mapping ππ from π into πΉ such that ππ =πon π. σΈ σΈ σΈ Since by Lemma 1 π is π(πΈ ,πΈ )-compact, πΜ is uniformly π’Μπ΄ Γβ β β Γπ΄ =π’ on π΄1 Γβ β β Γπ΄π. (28) π 1 π σΈ σΈ σΈ Μ π(πΈ ,πΈ )-continuous on π.Sinceππ =πon π΄, π is weakly This completes the proof. uniformly continuous on π΄. This implies (4).Itisclearthat (4) implies (1).Thiscompletestheproof. Lemma 4. Let πΈ be a locally convex space, let πΉ be a complete locally convex space, and let π’ be an π-linear mapping belonging π π σΈ σΈ π 3. The Tensor Product Representation of to πΏπ€( πΈ; .πΉ) Then, there exists π’βπΏΜ π( πΈ ;πΉ)with π’|πΈΜ =π’ σΈ σΈ σΈ such that π’Μ is π(πΈ ,πΈ )-continuous on π΄1 Γ β β β Γ π΄π for all Polynomials in Locally Convex Spaces absolutely convex bounded subsets π΄1,...,π΄π of πΈ. π For any π’βπΏπ( πΈ; ,wesetπΉ) Proof. By Lemma 3 for all absolutely convex bounded subsets 1 π΄ ,...,π΄ πΈ π(πΈσΈ σΈ ,πΈσΈ ) π (π’) (π₯ ,...,π₯ )= β π’(π₯ ,...,π₯ ) 1 π of , there exists a -continuous mapping 1 π π! π(1) π(π) (30) π’Μ π΄ Γβ β β Γπ΄ πΉ π’Μ =π’ π΄ Γβ β β Γ πβππ π΄1Γβ β β Γπ΄π from 1 π to with π΄1Γβ β β Γπ΄π on 1 π΄ π΄ ,...,π΄ ,π΅ ,...,π΅ π.If 1 π 1 π are absolutely convex bounded π for every (π₯1,...,π₯π)βπΈ,whereππ is the permutation group subsets of πΈ with π΄π β© π΅π =0ΜΈ for 1β€πβ€π,wehave of degree π.Then,π (π’) is a symmetric π-linear mapping from π π’Μ = π’Μ πΈ to πΉ satisfying π΄1Γβ β β Γπ΄π π΅1Γβ β β Γπ΅π (29) π’ (π₯,...,π₯) =π (π’)(π₯,...,π₯) on (π΄1 Γβ β β Γπ΄π)β©(π΅1 Γβ β β Γπ΅π).Thus,byLemma 1,we (31) σΈ σΈ π can define an n-linear mapping π’Μ from πΈ into πΉ by setting π π for every π₯βπΈ. We denote πΏπ( πΈ; πΉ) by the space of all π’=Μ π’Μπ΄ Γβ β β Γπ΄ on π΄1 Γ β β β Γ π΄π for all absolutely convex π 1 π symmetric π-linear mappings from πΈ to πΉ.LetΞ π be the bounded subsets π΄1,...,π΄π of πΈ.Then,themappingπ’Μ π mapping from πΈ into πΈ defined by satisfies all required conditions of this lemma. This completes the proof. Ξ π (π₯) = (π₯,...,π₯) for every π₯βπΈ. (32)
The following theorem is proved by Aron et al. [4], π For any π’βπΏπ( πΈ; ,πΉ) we define an π-homogeneous GonzalezΒ΄ and GutierrezΒ΄ [5], Honda et al. [6]. β polynomial Ξ π(π’) by Theorem 5. Let πΈ be a locally convex space and let πΉ be a π β complete locally convex space. Let πβπ(E;πΉ).Then,the Ξ π (π’) =π’βΞπ. (33) following statements are equivalent. π The mapping (1) πβππ€( πΈ; .πΉ) β π π π (2) For each absolutely convex bounded subset π of πΈ, π Ξ π :πΏπ ( πΈ; πΉ)π σ³¨βπ ( πΈ; πΉ) (34) σΈ σΈ σΈ ββ can be extended π(πΈ ,πΈ )-continuously to π ,where ββ σΈ σΈ σΈ π is the bipolar set of π for the dual pair β¨πΈ ,πΈ β©. is surjective. Abstract and Applied Analysis 5
π Theorem 6 (polarization formula). Let πβππ( πΈ; πΉ) and let For any π₯1 ββ β β βπ₯π β β¨ππΈ,weset π π β π’βπΏπ( πΈ; .IfπΉ) Ξ π(π’) =,then π 1 π (π₯1 ββ β β βπ₯π)= β π₯π(1) ββ β β βπ₯π(π). π π! (42) 1 πβππ π’ (π₯ ,...,π₯ ) = β π β β β π π (βπ π₯ ) . 1 π 2ππ! 1 π π π (35) β¨ πΈ β¨ πΈ ππ=Β±1 π=1 We denote by π,π the subspace of π generated by π (π₯1 ββ β β βπ₯π), π₯π βπΈ.Thespaceβ¨π,π πΈ is called the π-fold β πΈ β¨ πΈ By the above polarization formula, the mapping Ξ π : symmetric tensor product space of . Elements of π,π are π π π π πΏπ( πΈ; πΉ)π βπ ( πΈ; πΉ) is a linear isomorphism. called -symmetric tensors. Clearly, every tensor of the form π₯ββ β β βπ₯ We denote by β¨ππΈ the π-fold tensor product space of πΈ. is a symmetric tensor. Moreover, each element π π β¨ πΈ Let ππ be the linear mapping from πΈ into β¨ππΈ defined by in π,π can be expressed as a finite sum (not necessarily unique) of the form ππ (π₯1,...,π₯π)=π₯1 ββ β β βπ₯π (36) βπ₯ ββ β β βπ₯. π π (43) π π π for every (π₯1,...,π₯π)βπΈ.Foranyπ’βπΏπ( πΈ; ,πΉ) there exists πβ(π’) β πΏ (β¨ πΈ; πΉ) π β aunique π π π such that the diagram For any πβππ( πΈ; ,πΉ) there exists a unique ππ (π) β πΏπ(β¨π,π πΈ; πΉ) such that the diagram u p En F E F
β (37) in i (u) (44) n β πΏn jn (p) β¨ E n β¨ E n,s commutes. The mapping commutes. The mapping
πβ :πΏ (ππΈ; πΉ) σ³¨βπΏ (β¨πΈ; πΉ) β π π π π (38) ππ :ππ ( πΈ; πΉ) σ³¨βπΏπ (β¨πΈ; πΉ) (45) π π,π π π π π is a linear isomorphism. Each element of β¨ππΈ has a repre- is a linear isomorphism. Let π( πΈ; ,πΉ) πΏ( πΈ; ,andπΉ) πΏ ( πΈ; πΉ) sentation of the form be, respectively, the spaces of continuous π-homogeneous πΈ πΉ π β polynomials from into and the continuous symmetric - linear mappings from πΈ into πΉ. The restrictions βπ₯π,1 βπ₯π,2 ββ β β βπ₯π,π. (39) β π π π=1 Ξ π :πΏ(πΈ; πΉ) σ³¨β π( πΈ; πΉ) , β π π π However, this representation will never be unique. We Ξ π :πΏ ( πΈ; πΉ) σ³¨β π( πΈ; πΉ) , (46) denote by πΏπ the mapping of πΈ into β¨ππΈ defined by π :πΏ(ππΈ; πΉ)π σ³¨βπΏ (ππΈ; πΉ) πΏπ (π₯) =π₯ββ β β βπ₯ (40) are well-defined. For each πΌ β ππ (πΈ) and π=βπ π₯π ββ β β βπ₯π β for every π₯βπΈ. β¨π,π πΈ,weset
Proposition 7. Amappingπ:πΈis βπΉ an π-homogeneous π π ππΌ,π (π) = inf {βπΌ(π₯π) |π=βπ₯π ββ β β βπ₯π}. (47) polynomial if and only if there exists πβπΏπ( πΈ; πΉ) such that π π the diagram ππΌ,π is a seminorm on β¨π,π πΈ. We define the π-topology Ξ or the projective topology on β¨ πΈ as the locally convex E n En π,π topology generated by {ππΌ,π}πΌβππ (πΈ).Wedenotebyβ¨π,π ,ππΈ the
space endowed with π-topology and denote by β¨π,π ,ππΈ the completion β¨π,π ,ππΈ. Then, the following is valid (cf. Dineen p [2]). πΏn u (41) Proposition 8. Let πΈ be a locally convex space, then we have
πΏ(ππΈ; πΉ)β¨ β πΏ( πΈ; πΉ) , π.π β¨ E F (48) n T πΏπ (ππΈ; πΉ) β πΏ(β¨πΈ; πΉ) β π(ππΈ; πΉ) . commutes. π.π ,π 6 Abstract and Applied Analysis
σΈ σΈ σΈ σΈ σΈ σΈ σΈ Let E(πΈ ) be the family of all equicontinuous subsets of An π-homogeneous polynomial π on πΈ is π(πΈ ,πΈ )- σΈ σΈ σΈ σΈ σΈ σΈ σΈ πΈ with respect to the dual pair β¨πΈ ,πΈ β©. We denote by Oπ€β,π continuous on every equicontinuous subsets of πΈ if and only σΈ σΈ σΈ σΈ the family of subsets of πΈ defined by if π is ππ€β,π-continuous on πΈ .Thus,byPropositions9 and 11, we have the following theorem. σΈ σΈ Oπ€β,π = {π|πβπΈ ,πβ©πare Theorem 13. If an π-homogeneous polynomial π on πΈ is of σΈ σΈ σΈ σΈ σΈ π π πΈ π(πΈ ,πΈ ) -open in π for all πβE (πΈ )}. weaktypeifandonlyif is π-continuous in and continuous on πΈ with the initial topology of πΈ.
(49) Then, we can obtain the following topological tensor σΈ σΈ productrepresentationofpolynomialsofweaktype. We denote by ππ€β,π the topology on πΈ such that the family of all ππ€β,π-open sets coincides with Oπ€β,π.ByTheorem 5,the Theorem 14. Let πΈ be a DF space, then we have following is valid. πΏ(β¨πΈ ;πΉ)β©πΏ(β¨πΈ; )β π (ππΈ; πΉ) Proposition 9. π π πΈ π0 F π€ (53) A -homogeneous polynomial on is of π,π π π,π π weak type if and only if there exists a ππ€β,π-continuous π- Μ σΈ σΈ Μ homogeneous polynomial π on πΈ such that π=πon πΈ. for every complete locally convex space πΉ.
π β However, in general, the topology π€ ,π½ is not a locally A topological space π is called a π-space if its topology convex topology (cf. KomuraΒ― [7]). is localized on its compact set;, that is, πβπis open if and only if πβ©πΎis open in πΎ,withtheinducedtopology,for πΈ Definition 10. A locally convex space is called a DF-space if each compact subset πΎ of π.Amappingfromaπ-space into it contains a countable fundamental system of bounded sets a topological space is continuous if and only if its restriction and if the intersection of any sequence of absolutely convex to each compact set is continuous. neighborhoods of 0 which absorbs all bounded sets is itself a Let π’ beamappingfromalocallyconvexspaceπΈ into neighborhood of 0. a locally convex space πΉ.IfπΈ is a π-space and if π’ is σΈ π(πΈ, πΈ )-continuousoneveryboundedsubsetofπΈ,thenπ’ Grothendieck [8, 9] proved that the strong dual space of a is continuous on πΈ with the initial topology of πΈ.Thus,we metrizable locally convex space is a DF-space and the strong obtain the following theorem. dual space of a DF-space is a FrechetΒ΄ space. All Banach spaces are DF-spaces. The following result is Theorem 15. If πΈ is a DF space and a π-space, then we have known. Proposition 11 πΈ πΏ(β¨πΈ ;πΉ)β π (ππΈ; πΉ) (Banach-Dieudonnetheorem).Β΄ Let be a π0 π€ (54) σΈ π,π π metrizable locally convex space. Then, the topology ππ€β,π on πΈ is the topology of uniform convergence on all compact sets in πΈ. for every complete locally convex space πΉ. Proof. The proof is on KotheΒ¨ [10,Β§21β10]. If πΈ is a Banach space, then πΈ is a DF-space and a π-space. σΈ Thus, we have the following corollary. If πΈ is a DF space, then πΈπ½ is a FrechetΒ΄ space. Therefore, by Proposition 11 the following is valid. Corollary 16. If πΈ is a Banach space, then we have σΈ σΈ Proposition 12. The topology ππ€β,π on πΈ is the topology of πΈσΈ πΏ(β¨πΈ ;πΉ)β π (ππΈ; πΉ) uniform convergence on all compact sets in . π0 π€ (55) π,π π σΈ σΈ We denote by πΌπΎ the seminorm on πΈ defined by for every complete locally convex space πΉ. σ΅¨ σ΅¨ σΈ σΈ σ΅¨ σΈ σΈ σΈ σ΅¨ σΈ πΌπΎ (π₯ )=sup {σ΅¨β¨π₯ ,π₯ β©σ΅¨ |π₯ βπΎ} (50) Conflict of Interests σΈ for every compact subsets πΎ of πΈ . We denote by π0 the locally π½ The authors declare that there is no conflict of interests πΈσΈ σΈ convex topology on defined by the set of seminorms: regarding the publication of this paper. σΈ {πΌπΎ |πΎis every compact set of πΈ }. (51) Acknowledgments
We denote by πΈπ the locally convex space πΈ defined the set 0 KwangHoShonwassupportedbyBasicScienceResearch of seminorms: Program through the National Research Foundation of Korea {πΌ | |πΎ πΈσΈ }. (NRF) funded by the Ministry of Science and ICT and Future πΎ πΈ is every compact set of (52) Planning (2013R1A1A2008978). Abstract and Applied Analysis 7
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