On the set of weakly efficient minimizers for convex multiobjective programming

In this paper by employing an asymptotic approach we develop an existence and stability theory for convex multiobjective programming. We deal with the set of weakly efficient minimizers. To this end we employ a notion of convergence for vector-valued functions close to that due to Lemaire.     

Every null-additive set is meager-additive

It is proved that every null-additive subset of^ω2 is meager-additive. Several characterizations of the null-additive subsets of^ω2 are given, as well as a characterization of the meager additive subsets of^ω2. Under CH, an uncountable null-additive subset of^ω2 is constructed. Publ. No. 445. First version written in April 1991. Partially supported by the Basic Research Fund of the Israel Academy of Sciences and the Edmund Landau Center for Research in Mathematical Analysis, supported by the Minerva Foundation (Germany).     

Every three-point set is zero dimensional

This paper answers a question of Jan J. Dijkstra by giving a proof that all three-point sets are zero dimensional. It is known that all two-point sets are zero dimensional, and it is known that for all 3$">, there are -point sets which are not zero dimensional, so this paper answers the question for the last remaining case.

     

On the symmetry function of a convex set

We attempt a broad exploration of properties and connections between the symmetry function of a convex set S ${S \subset\mathbb{R}^n}We attempt a broad exploration of properties and connections between the symmetry function of a convex set S and other arenas of convexity including convex functions, convex geometry, probability theory on convex sets, and computational complexity. Given a point , let sym(x,S) denote the symmetry value of x in S: , which essentially measures how symmetric S is about the point x, and define x ^* is called a symmetry point of S if x ^* achieves the above maximum. The set S is a symmetric set if sym (S)=1. There are many important properties of symmetric convex sets; herein we explore how these properties extend as a function of sym (S) and/or sym (x,S). By accounting for the role of the symmetry function, we reduce the dependence of many mathematical results on the strong assumption that S is symmetric, and we are able to capture and otherwise quantify many of the ways that the symmetry function influences properties of convex sets and functions. The results in this paper include functional properties of sym (x,S), relations with several convex geometry quantities such as volume, distance, and cross-ratio distance, as well as set approximation results, including a refinement of the L?wner-John rounding theorems, and applications of symmetry to probability theory on convex sets. We provide a characterization of symmetry points x ^* for general convex sets. Finally, in the polyhedral case, we show how to efficiently compute sym(S) and a symmetry point x ^* using linear programming. The paper also contains discussions of open questions as well as unproved conjectures regarding the symmetry function and its connection to other areas of convexity theory. Dedicated to Clovis Gonzaga on the occasion of his 60th birthday.     

On stability of minimizers in convex programming

In this paper, we establish conditions ensuring Hölder and Lipschitz continuity of minimizers in convex programming. Lipschitz continuity is proved by establishing and applying a generalized version of the implicit function theorem.     

The image of a closed convex set under a Fredholm operator

The purpose of this article is two-fold. In the first place, we prove that a set is the image of a non empty closed convex subset of a real Banach space under an onto Fredholm operator of positive index if and only if it can be written as the union of {_Dn:n∈N}$\{D_n:n\in \mathbb{N}\}$, a non-decreasing family of non empty, closed, convex and bounded sets such that _Dn+_Dn+2⊆2_Dn+1$D_n+D_{n+2}\subseteq 2D_{n+1}$ for every n∈N$n\in \mathbb{N}$.     

A measurable cardinal with a closed unbounded set of inaccessibles from

We prove that is sufficient to construct a model in which is measurable and is a closed and unbounded subset of containing only inaccessible cardinals of . Gitik proved that is necessary.

We also calculate the consistency strength of the existence of such a set together with the assumption that is Mahlo, weakly compact, or Ramsey. In addition we consider the possibility of having the set generate the closed unbounded ultrafilter of while remains measurable, and show that Radin forcing, which requires a weak repeat point, cannot be improved on.

     

Stability of minimizers of set optimization problems

We study the asymptotic behavior of sequences of minimization problems in set optimization. More precisely, considering a sequence of set optimization problems \((P_n)\) converging in some sense to a set optimization problem (P) we investigate the upper and lower convergences of the sets of minimizers of the problems \((P_n)\) to the set of minimizers of the problem (P).     

A finite procedure for determining if a quadratic form is bounded below on a closed polyhedral convex set

Mathematical Programming -     

A closed (n + 1)-convex set inR 2 is a union ofn 6 convex sets

It is shown that if a closed setS in the plane is (n+1)-convex, then it has no more thann ⁴ holes. As a consequence, it can be covered by≤n ⁶ convex subsets. This is an improvement on the known bound of 2 ⁿ ·n ³. The author would like to thank the BSF for partially supporting this research. Publication no. 354.     

Unbounded components of the singular set of the distance function in

Given a closed set , the set of all points at which the metric projection onto is multi-valued is nonempty if and only if is nonconvex. The authors analyze such a set, characterizing the unbounded connected components of . For compact, the existence of an asymptote for any unbounded component of is obtained.

     

Convergence of relaxed minimizers in set optimization

In this paper we investigate, in a unified way, the stability of several relaxed minimizers of set optimization problems. To this end, we introduce a topology on vector ordered spaces from which we derive a concept of convergence that allows us to study both the upper and the lower stability of the sets of relaxed minimizers we consider.