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.     

Capacities in metric spaces

We discuss the potential theory related to the variational capacity and the Sobolev capacity on metric measure spaces. We prove our results in the axiomatic framework of [17].46E35, 31C15, 31C45     

Plasticity in metric spaces

In this paper we examine the properties of EC-plastic metric spaces, spaces which have the property that any noncontractive bijection from the space onto itself must be an isometry.     

Fuzzy metric spaces

In this paper, fuzzy metric spaces are redefined, different from the previous ones in the way that fuzzy scalars instead of fuzzy numbers or real numbers are used to define fuzzy metric. It is proved that every ordinary metric space can induce a fuzzy metric space that is complete whenever the original one does. We also prove that the fuzzy topology induced by fuzzy metric spaces defined in this paper is consistent with the given one. The results provide some foundations for the research on fuzzy optimization and pattern recognition.     

Weakly metric spaces

The paper contains some initial results of the theory of weakly metric spaces. The weak triangle axiom: for any ε > 0 there exists δ > 0 such that for any points x, y, and z with d(y, z) ≤ δ, the inequality d(x, z) ≤ d(x, y) + ε holds. __________ Translated from Zapiski Nauchnykh Seminarov POMI, Vol. 352, 2008, pp. 94–105.     

Counting metric spaces

If κ is a cardinal number, then any class of mutually non-homeomorphic metric spaces of size κ must be a set whose cardinality cannot exceed 2 ^κ . Our main result is a vivid construction of 2 ^κ mutually non-homeomorphic complete and both path connected and locally path connected metric spaces of size κ for each cardinal number κ from continuum up. Additionally we also deal with counting problems concerning countable metric spaces and Euclidean spaces.     

Embedding metric spaces into normed spaces and estimates of metric capacity

Let M^d{\cal M}^d be an arbitrary real normed space of finite dimension d ≥ 2. We define the metric capacity of M^d{\cal M}^d as the maximal m ? \Bbb Nm \in {\Bbb N} such that every m-point metric space is isometric to some subset of M^d{\cal M}^d (with metric induced by M^d{\cal M}^d ). We obtain that the metric capacity of M^d{\cal M}^d lies in the range from 3 to ë\frac32d û+1\left\lfloor\frac{3}{2}d\right\rfloor+1 , where the lower bound is sharp for all d, and the upper bound is shown to be sharp for d ∈ {2, 3}. Thus, the unknown sharp upper bound is asymptotically linear, since it lies in the range from d + 2 to ë\frac32d û+1\left\lfloor\frac{3}{2}d\right\rfloor+1 .     

Embedding metric spaces into normed spaces and estimates of metric capacity

Let be an arbitrary real normed space of finite dimension d ≥ 2. We define the metric capacity of as the maximal such that every m-point metric space is isometric to some subset of (with metric induced by ). We obtain that the metric capacity of lies in the range from 3 to , where the lower bound is sharp for all d, and the upper bound is shown to be sharp for d ∈ {2, 3}. Thus, the unknown sharp upper bound is asymptotically linear, since it lies in the range from d + 2 to . Research supported by the German Research Foundation, Project AV 85/1-1.     

Gated sets in metric spaces

The concept of a gated subset in a metric space is studied, and it is shown that properties of disjoint pairs of gated subsets can be used to investigate projections in Tits buildings.Dedicated to Professor Otto Haupt with best wishes on his 100th birthday     

KKM mappings in metric spaces

We introduce the class of KKM-type mappings on metric spaces and establish some fixed point theorems for this class. We also obtain a generalized Fan's matching theorem, a generalized Fan–Browder's type theorem, and a new version of Fan's best approximation theorem.     

The BV-capacity in metric spaces

We study basic properties of the BV-capacity and Sobolev capacity of order one in a complete metric space equipped with a doubling measure and supporting a weak Poincaré inequality. In particular, we show that the BV-capacity is a Choquet capacity and the Sobolev 1-capacity is not. However, these quantities are equivalent by two sided estimates and they have the same null sets as the Hausdorff measure of codimension one. The theory of functions of bounded variation plays an essential role in our arguments. The main tool is a modified version of the boxing inequality.     

Mutational equations in metric spaces

This paper summarizes an extension of differential calculus to a mutational calculus for maps from one metric space to another. The simple idea is to replace half-lines allowing to define difference quotients of maps and their various limits in the case of vector space by transitions with which we can also define differential quotients of a map. Their various limits are called mutations of a map. Many results of differential calculus and set-valued analysis, including the Inverse Function Theorem, do not really rely on the linear structure and can be adapted to the nonlinear case of metric spaces and exploited. Furthermore, the concept of differential equation can be extended tomutational equation governing the evolution in metric spaces. Basic Theorems as the Nagumo Theorem, the Cauchy-Lipschitz Theorem, the Center Manifold Theorem and the second Lyapunov Method hold true for mutational equations.This work was motivated by evolution equations of tubes in visual servoing on one hand, mathematical morphology on the other, when the metric spaces are power spaces. This paper begins by listing some consequences of general theorems concerning mutational equations for tubes.     

Convexity in finite metric spaces

A subsetS of a metric space (X,d) is calledd-convex if for any pair of pointsx,y S each pointz X withd(x,z) +d(z,y) =d(x,y) belongs toS. We give some results and open questions concerning isometric and convexity-preserving embeddings of finite metric spaces into standard spaces and the number ofd-convex sets of a finite metric space.     

Arc curvature in metric spaces

Concepts for curvature of arcs in metric geometry (specifically, Menger curvature κ _M , Haantjes-Finsler curvature κ _H , and transverse curvature κ _T introduced earlier by the author) are compared with respect to existence and numerical values. If a metric space satisfies a certain metric inequality shared in particular by Riemannian spaces, then the pointwise existence of κ _M on any arc implies that of κ _T and the two are equal. In a Minkowskian plane X with strictly convex unit sphere whose boundary U has a C ² polar representation ρ=ρ(θ), and with \(\bar \kappa _M\) and \(\bar \kappa _M\) the Menger and transverse curvatures relative to the underlying Euclidean metric, the following formulas are proved: At any point p on an arc at which \(\bar \kappa _M\) and \(\bar \kappa _M\) exist, $$\kappa _M = \bar \kappa _M \sqrt {\rho ^{2 + } 2\rho ^{'2 - } \rho \rho }$$ and $$\kappa _T = \bar \kappa _T \frac{{\sigma _1^{3/2} (T_p )}}{{\sigma _2 (T_p ,T_p^ \bot )}},$$ where T _pis the tangent at p, T ^⊥ _pthat line to which T _pis metrically perpendicular, and σ₁ and σ₂ are certain real-valued functions defined on lines of X. The result of this is that if κ* is the classical curvature of U _p≡U+p at U _p∩ T _p, $$\frac{{\kappa _M^2 }}{{\kappa _T^2 }} = \frac{{\kappa ^ * \sigma _1^{3/2} (T_p^ \bot )}}{{\sigma _2 \left( {T_p ,T_p^ \bot } \right)}},$$ from which it follows that the values of κ _M and κ _T are not equal for metric spaces in general even when both exist.