On upper and lower δ-precontinuous multifunctions

In this paper we introduce and study δ-precontinuous multifunctions as a generalization of precontinuous multifunctions due to Popa [Problemy Mat. 10 (1988) 9]. Some characterizations and several properties concerning upper (lower) δ-precontinuous multifunctions are obtained. The relationships between upper (lower) δ-precontinuous multifunctions and some known concepts are also discussed.     

An application of continuous fuzzy multifunctions

In this paper, the upper and lower δ-continuous multifunctions in fuzzy setting have been presented as a strong form and an application of fuzzy continuous multifunctions. Certain characterizations and several properties of these fuzzy multifunctions along with their mutual relationships are obtained. Attempts are also made to correlate this new class with the corresponding known types of fuzzy multifunctions. Also, applicability of the above new concepts to superstrings and space time could be probably possible in the near future.     

On Upper and Lower Almost β-continuous Multifunctions

In this paper, the authors define a multifunction F : X Y to be upper (lower) almost -continuous if F+(V) (F- (V)) is -open in X for every regular open set V of Y. They obtain some characterizations and several properties concerning upper (lower) almost -continuous multifunctions.     

Operation approaches on α-γ-I-open sets and α-γ-I-continuous functions in topological spaces

In this paper, the notion of α-γ-I-open sets in a topological space together with its corresponding interior and closure operators are introduced. Further, the concept of α-γ-I-continuous functions and α-γ-I-open functions are introduced and some of their basic properties are studied.     

Points of monotonicity in Orlicz-Lorentz function spaces

In Orlicz-Lorentz function space ?_M,ω[0,γ), points of upper monotonicity, lower monotonicity, upper local uniform monotonicity (γ<∞) and lower local uniform monotonicity (γ<∞) are characterized. As the corollary, we can easily obtain the criteria for strict monotonicity, upper local uniform monotonicity (γ<∞) and lower local uniform monotonicity (γ<∞) of ?_M,ω[0,γ).     

Properties of (θ,s)-continuous functions

Joseph and Kwack [Proc. Amer. Math. Soc. 80 (1980) 341–348] introduced the notion of (θ,s)-continuous functions in order to investigate S-closed spaces due to Thompson [Proc. Amer. Math. Soc. 60 (1976) 335–338]. In this paper, further properties of (θ,s)-continuous functions are obtained and relationships between (θ,s)-continuity, contra-continuity and regular set-connectedness defined by Dontchev et al. [Internat. J. Math. Math. Sci. 19 (1996) 303–310 and elsewhere] are investigated.     

The Delay-Capacity product for store-and-forward communication networks: Tree networks

A store-and-forward communication network under a maximal message delay criterion is considered. It is shown that the overall channel capacityC and the associated minimal maximal delayγ, as well as the maximal delayγ and the associated minimal overall capacityC, are characterized by a unique Delay-Capacity (γC) product number. The latter is related to a Delay-Capacity product (γC)⁺ number, uniquely determined solely by the topological structure of the communication network. Basic characteristics of the optimal delay and capacity assignment, a useful algoritm for the calculation of (γC)⁺ and simple upper and lower bounds on (γC)⁺, are derived for store-and-forward tree networks. Synthesis considerations and applications to hierarchical communication networks are noted.     

On generalized cluster sets of functions and multifunctions

This paper introduces and studies generalized cluster sets (g-cluster sets) of functions and multifunctions on GTS, which unifies the existing notions of cluster sets, θ-cluster sets, δ-cluster sets, S-cluster sets, s-cluster sets, p-cluster sets and many more. Several properties of the functions and multifunctions as well as their range and domain spaces are observed via degeneracies of their g-cluster sets. Characterizations of g-cluster sets through filterbases and grills on a typical class of GTS’s are also obtained. Moreover, μ-compactness of a GTS is characterized through g-cluster sets of multifunctions.     

Dense selections

Let X and Y be separable metric spaces and let Γ: X → CL(Y) be a multifunction with a closed graph. A selection f: X → Y for Γ is called dense if the closure of the graph of f is the graph of Γ. The main result of this paper characterizes those multifunctions admitting dense selections when X is complete and Y is sigma compact and complete. Moreover, the selection can always be chosen to be of Baire class two. In a much less restrictive setting, lower semicontinuous multifunctions admitting dense selections are those that map isolated points to singletons, an obvious necessary condition.     

Contractive multifunctions, fixed point inclusions and iterated multifunction systems

We study the properties of multifunction operators that are contractive in the Covitz-Nadler sense. In this situation, such operators T possess fixed points satisfying the relation x∈Tx. We introduce an iterative method involving projections that guarantees convergence from any starting point x₀∈X to a point x∈XT, the set of all fixed points of a multifunction operator T. We also prove a continuity result for fixed point sets XT as well as a “generalized collage theorem” for contractive multifunctions. These results can then be used to solve inverse problems involving contractive multifunctions. Two applications of contractive multifunctions are introduced: (i) integral inclusions and (ii) iterated multifunction systems.     

A unified theory of contra-(μ,λ)-continuous functions in generalized topological spaces

We introduce a new notion called contra-(μ,λ)-continuous functions as functions on generalized topological spaces?[8]. We obtain some characterizations and several properties of such functions. The functions enable us to formulate a unified theory of several modifications of contra-continuity due to Dontchev?[18].     

Subdifferentials of multifunctions and Lagrange multipliers for multiobjective optimization

This paper investigates vector optimization problems with objective and the constraints are multifunctions. By using a special scalarization function introduced in optimization by Hiriart-Urruty, we establish optimality conditions in terms of Lagrange-Fritz-John and Lagrange-Kuhn-Tucker multipliers. When all the data of the problem are subconvexlike we derive the results by Li, and hence those of Lin and Corley. We also show how the generalized Moreau-Rockafellar type theorem to multifunctions obtained recently by Lin can be derived from the well-known results in scalar optimization. In the last, vector optimization problem in which objective and the constraints are defined by multifunctions and depends on a parameter u, and the resulting value multifunction M(u) are considered. With the help of the generalized Moreau-Rockafellar type theorem we establish the weak subdifferential of M in terms of the weak subdifferential of objective and constraint multifunctions.     

A note on W-I-continuous functions

In [1], Aç?kgöz et al. introduced and investigated the notions of w-I-continuous and w*-I-continuous functions in ideal topological spaces. In this paper, we investigate their relationships with continuous and θ-continuous functions.     

Image Space Analysis and Scalarization for ε-Optimization of Multifunctions

Vector constrained problems for multifunctions are considered. Under an assumption based on generalized sections of the feasible set, some results in ε-optimization are achieved. In particular, necessary and sufficient conditions for scalarization of ε-optimization for multifunctions are deduced.     

On coloring problems with local constraints

We show complexity results for some generalizations of the graph coloring problem on two classes of perfect graphs, namely clique trees and unit interval graphs. We deal with the μ-coloring problem (upper bounds for the color on each vertex), the precoloring extension problem (a subset of vertices colored beforehand), and a problem generalizing both of them, the (γ, μ)-coloring problem (lower and upper bounds for the color on each vertex). We characterize the complexity of all those problems on clique trees of different heights, providing polytime algorithms for the cases that are easy. These results have two interesting corollaries: first, one can observe on clique trees of different heights the increasing complexity of the chain k-coloring, μ-coloring, (γ, μ)-coloring, list-coloring. Second, clique trees of height 2 are the first known example of a class of graphs where μ-coloring is polynomial time solvable and precoloring extension is NP-complete, thus being at the same time the first example where μ-coloring is polynomially solvable and (γ, μ)-coloring is NP-complete. Last, we show that the μ-coloring problem on unit interval graphs is NP-complete. These results answer three questions from [Ann. Oper. Res. 169(1) (2009), 3–16].     

Every compact group arises as the outer automorphism group of a II1 factor

We show that any compact group can be realized as the outer automorphism group of a factor of type II₁. This has been proved in the abelian case by Ioana, Peterson and Popa [A. Ioana, J. Peterson, S. Popa, Amalgamated free products of w-rigid factors and calculation of their symmetry group, math.OA/0505589, Acta Math., in press] applying Popa's deformation/rigidity techniques to amalgamated free product von Neumann algebras. Our methods are a generalization of theirs.     

Weakly upper Lipschitz multifunctions and applications in parametric optimization

The main purpose of this paper is to report on our studies of the weak upper Lipschitz and weak -upper Lipschitz continuities of multifunctions. Comparisons with other related Lipschitz-type continuities and calmness are given. When the concept of the weak upper Lipschitz continuities is applied to the special cases of constraint multifunctions, such as ones defined by a systems of equalities and inequalities or by a generalized equation we obtain the equivalent conditions with linear functional error bounds. Some results on the perturbation and penalty issues in parametric optimization problems are obtained under weak upper Lipschitz continuity assumptions on the constraint multifunctions. We also discuss the weak -upper Lipschitz continuity of a inverse subdifferential.Mathematics Subject Classification (2000): 49J52, 49J53, 90C25Acknowledgement The author thanks the associate editor and the referees for their helpful suggestions and comments.     

A V-cycle multigrid method for a viscoelastic fluid flow satisfying an Oldroyd-B-type constitutive equation

A V-cycle multigrid method is developed for a time-dependent viscoelastic fluid flow satisfying an Oldroyd-B-type constitutive equation in two-dimensional domains. Also existence, uniqueness, and error estimates of an approximate solution are discussed. The approximate stress, velocity, and pressure are, respectively, σ _k -discontinuous, u _k -continuous, and p _k -continuous.     

On upper and lower D*-supercontinuous multifunctions

We define a multifunction F: X ⇝ Y to be upper (lower) D*-supercontinuous if F ⁺(V) (F ⁻(V)) is d*-open in X for every open set V of Y. We obtain some characterizations and several properties concerning upper (lower) D*-supercontinuous multifunctions.