Powered by OpenAIRE graph
Found an issue? Give us feedback
image/svg+xml Jakob Voss, based on art designer at PLoS, modified by Wikipedia users Nina and Beao Closed Access logo, derived from PLoS Open Access logo. This version with transparent background. http://commons.wikimedia.org/wiki/File:Closed_Access_logo_transparent.svg Jakob Voss, based on art designer at PLoS, modified by Wikipedia users Nina and Beao Journal of Mathemati...arrow_drop_down
image/svg+xml Jakob Voss, based on art designer at PLoS, modified by Wikipedia users Nina and Beao Closed Access logo, derived from PLoS Open Access logo. This version with transparent background. http://commons.wikimedia.org/wiki/File:Closed_Access_logo_transparent.svg Jakob Voss, based on art designer at PLoS, modified by Wikipedia users Nina and Beao
Journal of Mathematical Sciences
Article . 1996 . Peer-reviewed
License: Springer TDM
Data sources: Crossref
image/svg+xml Jakob Voss, based on art designer at PLoS, modified by Wikipedia users Nina and Beao Closed Access logo, derived from PLoS Open Access logo. This version with transparent background. http://commons.wikimedia.org/wiki/File:Closed_Access_logo_transparent.svg Jakob Voss, based on art designer at PLoS, modified by Wikipedia users Nina and Beao
zbMATH Open
Article . 1996
Data sources: zbMATH Open
versions View all 2 versions
addClaim

Paraconvexity of the graphs of lipschitzian functions

Paraconvexity of the graphs of Lipschitzian functions
Authors: Semenov, P. V.;

Paraconvexity of the graphs of lipschitzian functions

Abstract

Following \textit{E. Michael} [Math. Scand. 7, 372-376 (1960; Zbl 0093.12001)] a closed subset \(P\) of a Banach space \(B\) is called \(\alpha\)-paraconvex if for \(x\in B\), \(r> \text{dist} (x,P)\) and \(y\in\text{conv} (P\cap K(x,r))\) we have \(\text{dist} (y,P)\leq \alpha \cdot r\), where \(K(x,r): =\{z\in B:|z-x |\leq r\}\). Each lsc multifunction defined on a paracompact space \(T\) and having \(\alpha\)-paraconvex values \(F(t) \subset B\) admits a continuous selection \(f:T\to B\) if \(0\leq \alpha<1\). In the paper under review it is proved, by using direct geometrical considerations, that if \(B=X \oplus Y\), where \(x=\mathbb{R}^n\), \(Y=\mathbb{R}\), then the graphs of \(k\)-Lipschitzian functions \(g:X\to Y\) with the same constant \(k\) are \(\alpha \)-paraconvex and an explicit formula for \(\alpha\) is given. The paper contains four questions concerning the optimisation of the values of \(\alpha\) and the possibility of replacing \(X\) and \(Y\) by arbitrary Hilbert spaces, or \(Y\) by \(\mathbb{R}^n\). Reviewers notes: 1. A. Maliszewski in a private communication to the reviewer indicates the following counterexample: Let \(f:\mathbb{R} \to \mathbb{R}^2\), with the sup norm, be such that \(f(-3)= (-3,3)\), \(f(-1)= (-3,-3)\), \(f(1)= (3,-3)\), \(f(3)= (3,3)\), \(f\) periodic with the period 8 and linear in the segments \([-3,-1]\), \([-1,1]\), \([1,3]\) and \([3,5]\). Then \(f\) is Lipschitzian with \(k=3\), but the graph of \(f\) is not \(\alpha\)-paraconvex. Nevertheless a multifunction \(F:\mathbb{R}^n \to\mathbb{R}^3\), whose values are graphs of \(f\in\text{Lip}_3 (\mathbb{R}, \mathbb{R}^2)\) has continuous selection. 2. The paper contains some misprints: \(e_1, \dots, e_n\) cannot create a base for \((n+1)\)-dimensional \(V_{n+1}\) on p. 239 and for the set \(W\) on the same page the assumption of closedness is necessary.

Keywords

multifunction, Lipschitz (Hölder) classes, Selections in general topology, paraconvex set, Variants of convex sets (star-shaped, (\(m, n\))-convex, etc.), Lipschitz map

  • BIP!
    Impact byBIP!
    selected citations
    These citations are derived from selected sources.
    This is an alternative to the "Influence" indicator, which also reflects the overall/total impact of an article in the research community at large, based on the underlying citation network (diachronically).
    1
    popularity
    This indicator reflects the "current" impact/attention (the "hype") of an article in the research community at large, based on the underlying citation network.
    Average
    influence
    This indicator reflects the overall/total impact of an article in the research community at large, based on the underlying citation network (diachronically).
    Average
    impulse
    This indicator reflects the initial momentum of an article directly after its publication, based on the underlying citation network.
    Average
Powered by OpenAIRE graph
Found an issue? Give us feedback
selected citations
These citations are derived from selected sources.
This is an alternative to the "Influence" indicator, which also reflects the overall/total impact of an article in the research community at large, based on the underlying citation network (diachronically).
BIP!Citations provided by BIP!
popularity
This indicator reflects the "current" impact/attention (the "hype") of an article in the research community at large, based on the underlying citation network.
BIP!Popularity provided by BIP!
influence
This indicator reflects the overall/total impact of an article in the research community at large, based on the underlying citation network (diachronically).
BIP!Influence provided by BIP!
impulse
This indicator reflects the initial momentum of an article directly after its publication, based on the underlying citation network.
BIP!Impulse provided by BIP!
1
Average
Average
Average
Upload OA version
Are you the author of this publication? Upload your Open Access version to Zenodo!
It’s fast and easy, just two clicks!