Inequalities in metric spaces with applications

Analogues of the parallelogram identity and the (CN) inequality of Bruhat and Tits in uniformly convex metric spaces are established. As an application of the new inequalities, we prove two fixed point results for single-valued and multi-valued Lipschitzian mappings.     

Lagrange multiplier rules for extremals in linear spaces

The aim of this paper is to formulate extremals in real, linear spaces, and to derive necessary conditions in the form of Lagrange multiplier rules for the extremals. Using a separation of intrinsic cores in real, linear spaces, the multiplier rules are proved under some conditions.The author wishes to thank the referee for a number of valuable suggestions, particularly the proof of Theorem 3.1.     

The metric gradient in normed linear spaces

Summary In this paper we give a definition for the gradient of a functional defined on a normed linear space which in the case of Hilbert space reduces to the usual definition. We also establish some interesting properties of the gradient which allow us to extend the well-known theorem of Curry to a large class of normed linear spaces.A part of this research was sponsored by the U.S. Army under contract No. DA-31-124-ARO-D-462.     

Characterization of convexZ-sets in linear metric spaces

L'vov State University. Translated from Funktsional'nyi Analiz i Ego Prilozheniya, Vol. 28, No. 4, pp. 77–79, October–December, 1994.     

Hyperspaces of compact sets in metric linear spaces

We write 2^x for the hyperspace of all non-empty compact sets in a complete metric linear space X topologized by the Hausdorff metric. Using the notation $\text{F}$(X) = {A ϵ 2^X: A is finite}, l^f₂ = {x} = (x_i) ϵ l₂: x_i = 0 for almost all i}, and l^σ₂ = {x = (x _i) ϵ l₂:σ^∞_i=1 (ix_i)² < ∞}, we have the following theorem:A family $\text{G}$ ⊂$\text{F}$(X) is homeomorphic to l^f₂ if $\text{G}$ is σ-fd-compact, the closure $\text{G}$ of $\text{G}$ in 2^x is not locally compact and if whenever A, B ∈ $\text{G}$, λ ∈ [0, 1] and C ⊂ λA + (1 - λ)B with card C⩽ max{card A, card B} then C ϵ $\text{G}$.Moreover, for any G_δ-AR-set $\text{G}$$\text{G}$ of $\text{G}$ with $\text{G}$$\text{G}$ ⊃ $\text{G}$ we have ($\text{G}$$\text{G}$, $\text{G}$)≅(l₂, l^ƒ₂).Similar conditions for hyperspaces to be homeomorphic to l^σ₂ are also established.     

Jensen's inequality for random elements in metric spaces and some applications

Jensen's inequality is extended to metric spaces endowed with a convex combination operation. Applications include a dominated convergence theorem for both random elements and random sets, a monotone convergence theorem for random sets, and other results on set-valued expectations in metric spaces and on random probability measures.     

CHARACTERIZATION OF BEST APPROXIMATIONS IN METRIC LINEAR SPACES

Let (X,d) be a real metric linear space, with translation-invariant metric d and G a linear subspace of X. In this paper we use functionals in the Lipschitz dual of X to characterize those elements of G which are best approximations to elements of X. We also give simultaneous characterization of elements of best approximation and also consider elements of ε-approximation.     

Bounded compactness of sets in linear metric spaces

An analog of the well known concept of bounded compactness from the theory of normed spaces is investigated in a linear metric space X. From the results obtained follows, for example, a sufficient condition for approximative compactness of a finite-dimensional subspace Lx.Translated from Matematicheskie Zametki, Vol. 11, No. 6, pp. 651–660, June, 1972.     

Hardy spaces H~p over non-homogeneous metric measure spaces and their applications

Let(X,d,)be a metric measure space satisfying both the geometrically doubling and the upper doubling conditions.Let ρ∈(1,∞),0p≤1≤q≤∞,p≠q,γ∈[1,∞)and ∈∈(0,∞).In this paper,the authors introduce the atomic Hardy space Hp,q,γ atb,ρ(μ)and the molecular Hardy space Hp,q,γ,mb,ρ∈(μ)via the discrete coefficient K(ρ),p B,S,and prove that the Calder′on-Zygmund operator is bounded from Hp,q,γ,δmb,ρ(μ)(or Hp,q,γatb,ρ(μ))into Lp(μ),and from Hp,q,γ+1atb,ρ(ρ+1)(μ)into H p,q,γ,12(δ-νp+ν)mb,ρ(μ).The boundedness of the generalized fractional integral Tβ(β∈(0,1))from Hp1,q,γ,θmb,ρ(μ)(or Hp1,q,γatb,ρ(μ))into Lp2(μ)with 1/p2=1/p1-β is also established.The authors also introduce theρ-weakly doubling condition,withρ∈(1,∞),of the measure and construct a non-doubling measure satisfying this condition.If isρ-weakly doubling,the authors further introduce the Campanato space Eα,qρ,η,γ(μ)and show that Eα,qρ,η,γ(μ)is independent of the choices ofρ,η,γand q;the authors then introduce the atomic Hardy space Hp,q,γatb,ρ(μ)and the molecular Hardy space Hp,q,γ,mb,ρ(μ),which coincide with each other;the authors finally prove that Hp,q,γatb,ρ(μ)is the predual of E1/p-1,1ρ,ρ,1(μ).Moreover,if is doubling,the authors show that Eα,qρ,η,γ(μ)and the Lipschitz space Lipα,q(μ)(q∈[1,∞)),or Hp,q,γatb,ρ(μ)and the atomic Hardy space Hp,q at(μ)(q∈(1,∞])of Coifman and Weiss coincide.Finally,if(X,d,)is an RD-space(reverse doubling space)with(X)=∞,the authors prove that Hp,q,γatb,ρ(μ),Hp,q,γ,mb,ρ(μ)and Hp,q at(μ)coincide for any q∈(1,2].In particular,when(X,d,):=(RD,||,dx)with dx being the D-dimensional Lebesgue measure,the authors show that spaces Hp,q,γatb,ρ(μ),Hp,q,γ,mb,ρ(μ),Hp,q,γatb,ρ(μ)and Hp,q,γ,mb,ρ(μ)all coincide with Hp(RD)for any q∈(1,∞).     

Chain rules for coderivatives of multivalued mappings in Banach spaces

Our basic object in this paper is to establish calculus rules for coderivatives of multivalued mappings between Banach spaces. We consider the coderivative which is associated to some geometrical approximate subdifferential for functions.

     

The contraction linear metric projections inL p spaces

In this paper, we study the contraction linearity for metric projection in Lp spaces. A geometrical property of a subspace Y of Lp is given on which Pr is a contraction projection.     

Linear operators in spaces with indefinite metric and their applications

The paper contains a survey of papers reviewed in Ref. Zh. Matematika from 1953–1978 on the theory of linear operators in (mainly Hibert) spaces with indefinite metric and their applications to various domains of mathematics and mechanics. As a preliminary, the needed results on the geometry of spaces with indefinite metric are described.Translated from Itogi Nauki i Tekhniki, Matematicheskii Analiz, Vol. 17, pp. 113–206, 1979.     

Strict sums and semicontinuity below metric projections in linear normed spaces

The relationships, are studied between strict suns [1] and sets with semicontinuous below metric projections, and also certain general properties of these classes of sets in linear normed spaces. There are characterized finite-dimensional normed spaces in which the class of strict suns coincides with the class of nonvacuous closed sets having semicontinuous below metric projections. It is proven that a P-connected [1] set with semicontinuous below (semicontinuous above) metric projections is V-connected [1].Translated from Matematicheskie Zametki, Vol. 23, No. 4, pp. 563–572, April, 1978.     

Ultrametricity and metric betweenness in tangent spaces to metric spaces

The paper deals with pretangent spaces to general metric spaces. An ultrametricity criterion for pretangent spaces is found and it is closely related to the metric betweenness in the pretangent spaces.