Persistence Terrace for Topological Inference of Point Cloud Data

Topological data analysis (TDA) is a rapidly developing collection of methods for studying the shape of point cloud and other data types. One popular approach, designed to be robust to noise and outliers, is to first use a smoothing function to convert the point cloud into a manifold and then apply persistent homology to a Morse filtration. A significant challenge is that this smoothing process involves the choice of a parameter and persistent homology is highly sensitive to that choice; moreover, important scale information is lost. We propose a novel topological summary plot, called a persistence terrace, that incorporates a wide range of smoothing parameters and is robust, multi-scale, and parameter-free. This plot allows one to isolate distinct topological signals that may have merged for any fixed value of the smoothing parameter, and it also allows one to infer the size and point density of the topological features. We illustrate our method in some simple settings where noise is a serious issue for existing frameworks and then we apply it to a real dataset by counting muscle fibers in a cross-sectional image. Supplementary material for this article is available online.     

Lʼindice des champs de vecteurs sur les courbes de Cohen–Macaulay

In this paper a new method for computing the topological index of a vector field at Cohen–Macaulay curves is described. It is based on properties of regular meromorphic differential forms which are used for computing the homological index of vectors fields introduced by X. Gómez-Mont. In particular, we show how to compute the index at quasihomogeneous Gorenstein curves and complete intersections, at monomial curves, at Cohen–Macaulay space curves, and others. In contrast to previous articles on this subject we do not use the technique of spectral sequences, or computer algebra systems for symbolic calculations.     

Study of generalized eigenfunctions of a perturbed isotropic elastic half‐space

We consider the self‐adjoint operator governing the propagation of elastic waves in a perturbed isotropic half‐space (perturbation with compact support of a homogeneous isotropic half‐space) with a free boundary condition. We propose a method to obtain, numerical values included, a complete set of generalized eigenfunctions that diagonalize this operator. The first step gives an explicit representation of these functions using a perturbative method. The unbounded boundary is a new difficulty compared with the method used by Wilcox [25], who set the problem in the complement of bounded open set. The second step is based on a boundary integral equations method which allows us to compute these functions. For this, we need to determine explicitly the Green's function of (A₀ – ω²), where A₀ is the self‐adjoint operator describing elastic waves in a homogeneous isotropic half‐space. Copyright © 2000 John Wiley & Sons, Ltd.     

A Common Fixed Point Theorem with Applications

In this paper, we establish a common fixed point theorem for a family of self set-valued mappings on a compact and convex set in a locally convex topological vector space. As applications, we obtain an existence theorem of solutions for a variational inequality of Stampacchia type and some Ky Fan-type minimax inequalities.     

Real structures of Teichmüller spaces, Dehn twists, and moduli spaces of real curves

An orientation reversing involution of a topological compact genus surface induces an antiholomorphic involution of the Teichmüller space of genus g Riemann surfaces. Two such involutions and are conjugate in the mapping class group if and only if the corresponding orientation reversing involutions and of are conjugate in the automorphism group of . This is equivalent to saying that the quotient surfaces and are homeomorphic. Hence the Teichmüller space has distinct antiholomorphic involutions, which are also called real structures of ([7]). This result is a simple fact that follows from Royden's theorem ([4]) stating that the the mapping class group is the full group of holomorphic automorphisms of the Teichmüller space (). Let and be two real structures that are not conjugate in the mapping class group. In this paper we construct a real analytic diffeomorphism such that This mapping d is a product of full and half Dehn–twists around certain simple closed curves on the surface . This has applications to the moduli spaces of real algebraic curves. A compact Riemann surface admitting an antiholomorphic involution is a real algebraic curve of the topological type . All fixed–points of the real structure of the Teichmüller space , are real curves of the above topological type and every real curve of that topological type is represented by an element of the fixed–point set of . The fixed–point set is the Teichmüller space of real algebraic curves of the corresponding topological type. Given two different real structures and , let d the the real analytic mapping satisfying (1). It follows that d maps onto and is an explicit real analytic diffeomorphism between these Teichmüller spaces. Received 8 December 1997; accepted 12 August 1998     

Lokalkreisförmige Vektorgruppen

We define locally circled vector groups as topological vector spaces over the discrete real or complex numberfield with a neighbourhoodbase of zero consisting of circled sets. Every topological vector space is a locally circled vector group. Topological vector groups and especially locally circled vector groups have useful applications to topological vector spaces and this paper is intended as an introduction to the theory of locally circled vector groups. Continuations including applications to topological vector spaces will follow. Here we study the structure of finite dimensional and locally compact vector groups, describe those locally circled vector groups which have a generating precompact circled set and finally prove some theorems about convex sets in these spaces.     

The invariant subspace problem

A fundamental problem is to determine whether every bounded linear transformation in Hilbert space has a nontrivial invariant subspace. A formal proof [1] of the existence of invariant subspaces is given by the theory of square summable power series [2] in its vector formulation [3]. A determination of extreme points of a convex set remains for the justification of the formal argument. A characterization of extreme points which implies the existence of invariant subspaces has been conjectured [4]. New information is obtained from a localization of the theory of square summable power series [5] which allows the formulation of extreme point problems which are closely related because of the Carathéodory-Fejér extension theorem [6]. The conjectured characterization of extreme points is shown to be false. Extreme points need not have the properties required for the construction of invariant subspaces.     

On upper semicontinuity of global minima in constrained optimization problems

This paper studies stability properties of solutions for optimization problems subject to perturbations in constraints. For problems formulated in a complete metric space sufficient conditions for topological upper semicontinuity of the solution multifunction are derived without any compactness assumptions. When the feasible solution set is additionally assumed to be compact these conditions reduce to that of Berge (“Topological Spaces,” Macmillan Co., New York, 1963), and in that case they turn out to be also necessary.     

Stable sets and mean Li–Yorke chaos in positive entropy systems

It is shown that in a topological dynamical system with positive entropy, there is a measure-theoretically “rather big” set such that a multivariant version of mean Li–Yorke chaos happens on the closure of the stable or unstable set of any point from the set. It is also proved that the intersections of the sets of asymptotic tuples and mean Li–Yorke tuples with the set of topological entropy tuples are dense in the set of topological entropy tuples respectively.     

Step length problem for trimming curve approximation in tessellating trimmed surfaces

A trimmed parametric surface is mainly composed of a surface together with trimming curves lying in D, the parametric space of the surface. By investigating the interrelation between surface tessellation and trimming curve approximation, we point out some problems on trimming curve approximation in existing trimmed surface tessellation algorithms. Counter examples are presented to show that a valid approximation of trimming curves in D together with the refinement imposed by surface tessellation does not necessarily generate a valid linear approximation in 3D space. To assure the 3D derivation tolerance, we propose two novel step-length estimation methods such that a piecewise linear interpolant of the trimming curve based on the proposed step lengths will result in a valid linear approximation in 3D space. The first method exploits the triangle inequality and takes the derivation tolerance in 3D space into account to compute the effective step length. Our second method is based on segmenting the trimming curve into subcurves first and then approximates each subcurve according to the derivation tolerance in 3D space. Moreover, several empirical tests are given to demonstrate the correctness of our step length estimations.     

Matrices, graphs and equivalence relations

A suitable equivalence relation is introduced on the set of square matrices with entries of any kind. This allows us to associate to every equivalence class an infinite family of graphs and determine their topological properties. When a given square matrix is the multiplication table of a finite groupoid, some connections between algebraic properties of the groupoid and topological properties of these graphs are proved. Received: May 4, 1999 Published online: December 19, 2001     

A regular decomposition of the edge-product space of phylogenetic trees

We investigate the topology and combinatorics of a topological space called the edge-product space that is generated by the set of edge-weighted finite labelled trees. This space arises by multiplying the weights of edges on paths in trees, and is closely connected to tree-indexed Markov processes in molecular evolutionary biology. In particular, by considering combinatorial properties of the Tuffley poset of labelled forests, we show that the edge-product space has a regular cell decomposition with face poset equal to the Tuffley poset.     

On Existence of Solutions to Differential Equations or Inclusions Remaining in a Prescribed Closed Subset of a Finite-Dimensional Space

This paper is devoted to existence of trajectories to differential equations and inclusions remaining in a given closed (or compact) set. Topological properties of the boundary of this set enables us to conclude the existence of such trajectories in many cases.     

Soliton parameters and chaotic sets

In this work we apply a nonperturbative approach to analyze soliton bifurcation in the presence of surface tension, which is a reformulation of standard methods based on the reversibility properties of the system. The hypothesis is nonrestrictive and the results can be extended to a much wider variety of systems. The usual idea of tracking intersections of unstable manifolds with some invariant set is again used, but reversibility plays an important role establishing in a geometrical point of view some kind of symmetry which, in a classical way, is unknown or nonexistent. Using a computer program we determine soliton solutions and also their bifurcations in the space of parameters giving a picture of the chaotic structural distribution to phase and amplitude shift phenomena.     

Discussion of the Particle Finite Element Method in the Context of Strength of Materials

In the context of the particle finite element method (PFEM) a body is considered as a set of particles that are meshed with standard finite elements before every load step. This enables the method to cope with large topological changes where the standard FEM often fails. To mesh the set of particles, its boundary needs to be detected which is accomplished with the α-shape method, and although this method is often used within the PFEM, the crucial parameter α is not well understood. This article provides a physical interpretation of α and shows its meaning in the context of strength of materials. (© 2015 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)     

Sets, complements and boundaries

The relations among a set, its complement, and its boundary are examined constructively. A crucial tool is a theorem that allows the construction of a point where a segment comes close to the boundary of a set in a Banach space. Brouwerian examples show that many of the results are the best possible.     

一簇Lorenz映射的混沌行为的符号动力学分析

首先从符号动力学的角度论证了一簇Lorenz映射且有的混沌性质:稠密的周期轨道,周期的集合,拓扑熵,几乎所有(关于Lebesgue测度)的点的Lyapunov指数;并从揉序列的分析给出了该簇映射的拓扑熵的一个下界及Lyapunov指数的一个下界与上界,在很大程度上反应了Lorenz系统的复杂程度.其次仍从符号动力学的角度论证了更一般的Lorenz映射,通过设立参数空间,穷尽了Lorenz映射中函数为直线段的所有情况,并得出同前述Lorenz映射相似的且较为复杂的性质.     

On a Parameterized System of Nonlinear Equations with Economic Applications

We study a parameterized system of nonlinear equations. Given a nonempty, compact, and convex set, an affine function, and a point-to-set mapping from the set to the Euclidean space containing the set, we constructively prove that, under certain (boundary) conditions on the mapping, there exists a connected set of zero points of the mapping, i.e., the origin is an element of the image for every point in the connected set, such that the connected set has a nonempty intersection with both the face at which the affine function is minimized and the face at which that function is maximized. This result generalizes and unifies several well-known existence theorems including Browder??s fixed point theorem and Ky Fan??s coincidence theorem. An economic application with constrained equilibria is also discussed.     

Semi-cardinal interpolation and difference equations: From cubic B-splines to a three-direction box-spline construction

This paper considers the problem of interpolation on a semi-plane grid from a space of box-splines on the three-direction mesh. Building on a new treatment of univariate semi-cardinal interpolation for natural cubic splines, the solution is obtained as a Lagrange series with suitable localization and polynomial reproduction properties. It is proved that the extension of the natural boundary conditions to box-spline semi-cardinal interpolation attains half of the approximation order of the cardinal case.     

细长体截面绕流中的一种临界状态

应用拓扑分析的方法研究了细长体截面绕流拓扑结构的演变过程．指出随着细长体背涡的发展,导致截面流场的拓扑结构发生变化,会出现一种临界流动状态．在这种临界流态下,流场中会出现一种高阶奇点．这种高阶奇点的指数为-3/2．这种高阶奇点是结构不稳定的,稍有扰动就会产生分叉,使流场的拓扑结构发生变化．