Polynomial extreme elements of the closed unit ball ofH∞(B)

1994 ◽  
Vol 25 (1) ◽  
pp. 49-56 ◽  
Author(s):  
John N. McDonald
Keyword(s):  
Unit Ball ◽  
Closed Unit Ball

Weak-Star Continuous Analytic Functions

1995 ◽  
Vol 47 (4) ◽  
pp. 673-683 ◽  
Author(s):  
R. M. Aron ◽  
B. J. Cole ◽  
T. W. Gamelin
Keyword(s):  
Unit Ball ◽  
Finite Type ◽  
Analytic Functions ◽  
Approximation Property ◽  
Entire Functions ◽  
Open Unit ◽  
Closed Unit Ball ◽  
Open Unit Ball ◽  
Weakly Continuous ◽  
Weak Star

AbstractLet 𝒳 be a complex Banach space, with open unit ball B. We consider the algebra of analytic functions on B that are weakly continuous and that are uniformly continuous with respect to the norm. We show these are precisely the analytic functions on B that extend to be weak-star continuous on the closed unit ball of 𝒳**. If 𝒳* has the approximation property, then any such function is approximable uniformly on B by finite polynomials in elements of 𝒳*. On the other hand, there exist Banach spaces for which these finite-type polynomials fail to approximate. We consider also the approximation of entire functions by finite-type polynomials. Assuming 𝒳* has the approximation property, we show that entire functions are approximable uniformly on bounded sets if and only if the spectrum of the algebra of entire functions coincides (as a point set) with 𝒳**.

scholarly journals Semi-embeddings of Banach spaces which are hereditarily c0

1983 ◽  
Vol 26 (2) ◽  
pp. 163-167 ◽  
Author(s):  
L. Drewnowski
Keyword(s):  
Banach Space ◽  
Linear Operator ◽  
Vector Space ◽  
Unit Ball ◽  
Banach Spaces ◽  
Continuous Linear Operator ◽  
Closed Unit Ball ◽  
Continuous Linear ◽  
Scattered Space ◽  
Complete Set

Following Lotz, Peck and Porta [9], a continuous linear operator from one Banach space into another is called a semi-embedding if it is one-to-one and maps the closed unit ball of the domain onto a closed (hence complete) set. (Below we shall allow the codomain to be an F-space, i.e., a complete metrisable topological vector space.) One of the main results established in [9] is that if X is a compact scattered space, then every semi-embedding of C(X) into another Banach space is an isomorphism ([9], Main Theorem, (a)⇒(b)).

scholarly journals Complex extreme measurable selections

1995 ◽  
Vol 58 (2) ◽  
pp. 222-231
Author(s):  
Douglas Mupasiri
Keyword(s):  
Banach Space ◽  
Unit Ball ◽  
Extreme Point ◽  
Measure Space ◽  
Sufficient Conditions ◽  
Complex Banach Space ◽  
Closed Unit Ball ◽  
Measurable Selections ◽  
Necessary And Sufficient

AbstractWe give a characterization of complex extreme measurable selections for a suitable set-valued map. We use this result to obtain necessary and sufficient conditions for a function to be a complex extreme point of the closed unit ball of Lp (ω, Σ, ν X), where (ω, σ, ν) is any positive, complete measure space, X is a separable complex Banach space, and 0 < p < ∞.

$k$-smoothness: an answer to an open problem

2018 ◽  
Vol 123 (1) ◽  
pp. 85-90 ◽  
Author(s):  
Paweł Wójcik
Keyword(s):  
Unit Ball ◽  
Open Problem ◽  
Closed Unit Ball

The aim of this paper is to characterize the $k$-smooth points of the closed unit ball of $\mathcal{K}(\mathcal{H}_1;\mathcal{H}_2)$. In this paper we also answer a question posed by A. Saleh Hamarsheh in 2015.

scholarly journals Biduals of weighted banach spaces of analytic functions

1993 ◽  
Vol 54 (1) ◽  
pp. 70-79 ◽  
Author(s):  
K. D. Bierstedt ◽  
W. H. Summers
Keyword(s):  
Unit Ball ◽  
Banach Spaces ◽  
Open Subset ◽  
Analytic Functions ◽  
Holomorphic Functions ◽  
Supremum Norm ◽  
Closed Unit Ball ◽  
Weighted Banach Spaces ◽  
Spaces Of Analytic Functions ◽  
Continuous Weight

AbstractFor a positive continuous weight function ν on an open subset G of CN, let Hv(G) and Hv0(G) denote the Banach spaces (under the weighted supremum norm) of all holomorphic functions f on G such that ν f is bounded and ν f vanishes at infinity, respectively. We address the biduality problem as to when Hν(G) is naturally isometrically isomorphic to Hν0(G)**, and show in particular that this is the case whenever the closed unit ball in Hν0(G) in compact-open dense in the closed unit ball of Hν(G).

scholarly journals Remarks on retracting balls on spherical caps in \(c_{0}\), \(c\), \(l^{\infty }\) spaces

2020 ◽  
Vol 74 (1) ◽  
pp. 45
Author(s):  
Kazimierz Goebel
Keyword(s):  
Banach Space ◽  
Unit Ball ◽  
Unit Sphere ◽  
Uniform Norm ◽  
Sequence Spaces ◽  
Closed Unit Ball ◽  
Infinite Dimensional ◽  
Infinite Dimensional Banach Space ◽  
Lipschitz Constants ◽  
Spherical Caps

For any infinite dimensional Banach space there exists a lipschitzian retraction of the closed unit ball B onto the unit sphere S. Lipschitz constants for such retractions are, in general, only roughly estimated. The paper is illustrative. It contains remarks, illustrations and estimates concerning optimal retractions onto spherical caps for sequence spaces with the uniform norm.

scholarly journals Extreme points in spaces between Dirichlet and Vanishing Mean Oscillation

2003 ◽  
Vol 67 (3) ◽  
pp. 365-375
Author(s):  
K. J. Wirths ◽  
J. Xiao
Keyword(s):  
Unit Ball ◽  
Unit Circle ◽  
Dirichlet Space ◽  
Extreme Points ◽  
Closed Unit Ball ◽  
Mean Oscillation ◽  
Image Position ◽  
Complex Valued

For p ∈ (0, ∞) define Qp0(∂Δ) as the space of all Lebesgue measurable complex-valued functions f; on the unit circle ∂Δ for which ∫∂Δf;(z)|dz|/(2π) = 0 andas the open subarc I of ∂Δ varies. Note that each Qp,0(∂Δ) lies between the Dirichlet space and Sarason's vanishing mean oscillation space. This paper determines the extreme points of the closed unit ball of Qp,0(∂Δ) equipped with an appropriate norm.

scholarly journals Local properties of maps of the ball

2003 ◽  
Vol 2003 (2) ◽  
pp. 75-81
Author(s):  
Yakar Kannai
Keyword(s):  
Unit Ball ◽  
Half Space ◽  
Interior Point ◽  
Closed Unit Ball ◽  
Game Theoretic ◽  
Local Properties ◽  
Constant Mapping ◽  
Quasianalytic Functions

Letfbe an essential map ofSn−1into itself (i.e.,fis not homotopic to a constant mapping) admitting an extension mapping the closed unit ballB¯nintoℝn. Then, for every interior pointyofBn, there exists a pointxinf−1(y)such that the image of no neighborhood ofxis contained in a coordinate half space withyon its boundary. Under additional conditions, the image of a neighborhood ofxcovers a neighborhood ofy. Differential versions are valid for quasianalytic functions. These results are motivated by game-theoretic considerations.

On interpolation by analytic maps in infinite dimensions

1978 ◽  
Vol 83 (2) ◽  
pp. 243-252 ◽  
Author(s):  
J. Globevnik
Keyword(s):  
Unit Ball ◽  
Complex Banach Space ◽  
Open Unit ◽  
Closed Unit Ball ◽  
Infinite Dimensions ◽  
Open Unit Ball ◽  
Infinite Dimensional ◽  
Analytic Maps ◽  
Peak Interpolation ◽  
Vector Valued Functions

AbstractLet A be the complex Banach algebra of all bounded continuous complex-valued functions on the closed unit ball of a complex Banach space X, analytic on the open unit ball, with sup norm. For a class of spaces X which contains all infinite dimensional complex reflexive spaces we prove the existence of non-compact peak interpolation sets for A. We prove some related interpolation theorems for vector-valued functions and present some applications to the ranges of analytic maps between Banach spaces. We also show that in general peak interpolation sets for A do not exist.

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