Persistence, Metric Invariants, and Simplification
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Metric Geometry in a Tame Setting
University of California Los Angeles Metric Geometry in a Tame Setting A dissertation submitted in partial satisfaction of the requirements for the degree Doctor of Philosophy in Mathematics by Erik Walsberg 2015 c Copyright by Erik Walsberg 2015 Abstract of the Dissertation Metric Geometry in a Tame Setting by Erik Walsberg Doctor of Philosophy in Mathematics University of California, Los Angeles, 2015 Professor Matthias J. Aschenbrenner, Chair We prove basic results about the topology and metric geometry of metric spaces which are definable in o-minimal expansions of ordered fields. ii The dissertation of Erik Walsberg is approved. Yiannis N. Moschovakis Chandrashekhar Khare David Kaplan Matthias J. Aschenbrenner, Committee Chair University of California, Los Angeles 2015 iii To Sam. iv Table of Contents 1 Introduction :::::::::::::::::::::::::::::::::::::: 1 2 Conventions :::::::::::::::::::::::::::::::::::::: 5 3 Metric Geometry ::::::::::::::::::::::::::::::::::: 7 3.1 Metric Spaces . 7 3.2 Maps Between Metric Spaces . 8 3.3 Covers and Packing Inequalities . 9 3.3.1 The 5r-covering Lemma . 9 3.3.2 Doubling Metrics . 10 3.4 Hausdorff Measures and Dimension . 11 3.4.1 Hausdorff Measures . 11 3.4.2 Hausdorff Dimension . 13 3.5 Topological Dimension . 15 3.6 Left-Invariant Metrics on Groups . 15 3.7 Reductions, Ultralimits and Limits of Metric Spaces . 16 3.7.1 Reductions of Λ-valued Metric Spaces . 16 3.7.2 Ultralimits . 17 3.7.3 GH-Convergence and GH-Ultralimits . 18 3.7.4 Asymptotic Cones . 19 3.7.5 Tangent Cones . 22 3.7.6 Conical Metric Spaces . 22 3.8 Normed Spaces . 23 4 T-Convexity :::::::::::::::::::::::::::::::::::::: 24 4.1 T-convex Structures . -
On Asymmetric Distances
Analysis and Geometry in Metric Spaces Research Article • DOI: 10.2478/agms-2013-0004 • AGMS • 2013 • 200-231 On Asymmetric Distances Abstract ∗ In this paper we discuss asymmetric length structures and Andrea C. G. Mennucci asymmetric metric spaces. A length structure induces a (semi)distance function; by using Scuola Normale Superiore, Piazza dei Cavalieri 7, 56126 Pisa, Italy the total variation formula, a (semi)distance function induces a length. In the first part we identify a topology in the set of paths that best describes when the above operations are idempo- tent. As a typical application, we consider the length of paths Received 24 March 2013 defined by a Finslerian functional in Calculus of Variations. Accepted 15 May 2013 In the second part we generalize the setting of General metric spaces of Busemann, and discuss the newly found aspects of the theory: we identify three interesting classes of paths, and compare them; we note that a geodesic segment (as defined by Busemann) is not necessarily continuous in our setting; hence we present three different notions of intrinsic metric space. Keywords Asymmetric metric • general metric • quasi metric • ostensible metric • Finsler metric • run–continuity • intrinsic metric • path metric • length structure MSC: 54C99, 54E25, 26A45 © Versita sp. z o.o. 1. Introduction Besides, one insists that the distance function be symmetric, that is, d(x; y) = d(y; x) (This unpleasantly limits many applications [...]) M. Gromov ([12], Intr.) The main purpose of this paper is to study an asymmetric metric theory; this theory naturally generalizes the metric part of Finsler Geometry, much as symmetric metric theory generalizes the metric part of Riemannian Geometry. -
General Topology
General Topology Tom Leinster 2014{15 Contents A Topological spaces2 A1 Review of metric spaces.......................2 A2 The definition of topological space.................8 A3 Metrics versus topologies....................... 13 A4 Continuous maps........................... 17 A5 When are two spaces homeomorphic?................ 22 A6 Topological properties........................ 26 A7 Bases................................. 28 A8 Closure and interior......................... 31 A9 Subspaces (new spaces from old, 1)................. 35 A10 Products (new spaces from old, 2)................. 39 A11 Quotients (new spaces from old, 3)................. 43 A12 Review of ChapterA......................... 48 B Compactness 51 B1 The definition of compactness.................... 51 B2 Closed bounded intervals are compact............... 55 B3 Compactness and subspaces..................... 56 B4 Compactness and products..................... 58 B5 The compact subsets of Rn ..................... 59 B6 Compactness and quotients (and images)............. 61 B7 Compact metric spaces........................ 64 C Connectedness 68 C1 The definition of connectedness................... 68 C2 Connected subsets of the real line.................. 72 C3 Path-connectedness.......................... 76 C4 Connected-components and path-components........... 80 1 Chapter A Topological spaces A1 Review of metric spaces For the lecture of Thursday, 18 September 2014 Almost everything in this section should have been covered in Honours Analysis, with the possible exception of some of the examples. For that reason, this lecture is longer than usual. Definition A1.1 Let X be a set. A metric on X is a function d: X × X ! [0; 1) with the following three properties: • d(x; y) = 0 () x = y, for x; y 2 X; • d(x; y) + d(y; z) ≥ d(x; z) for all x; y; z 2 X (triangle inequality); • d(x; y) = d(y; x) for all x; y 2 X (symmetry). -
Homology Inference from Point Cloud Data
Homology Inference from Point Cloud Data Yusu Wang Abstract. In this paper, we survey a common framework of estimating topo- logical information from point cloud data (PCD) that has been developed in the field of computational topology in the past twenty years. Specifically, we focus on the inference of homological information. We briefly explain the main ingredients involved, and present some basic results. This chapter is part of the AMS short course on Geometry and Topology in Statistical Inference. It aims to introduce the general mathematical audience to the problem of topol- ogy inference, but is not meant to be a comprehensive review of the field in general. 1. Introduction The past two decades have witnessed tremendous development in the field of computational and applied topology. Much progress has been made not only in the theoretical and computational fronts, but also in the application of topological methods / ideas for data analysis. For example, on the theoretical front, there has been elegant work on the so-called persistent homology, originally proposed in [52] 1, and further developed in [15, 16, 19, 22, 33, 94] etc. On the application front, topological methods have been successfully used in fields such as computer graphics e.g, [67, 82, 42], visualization e.g, [10, 77, 76], geometric reconstruction and meshing e.g, [2, 41, 90], sensor network e.g, [38, 39, 61, 88, 91], high dimensional data analysis e.g, [59, 60, 84, 89] and so on. Indeed, topological data analysis (TDA) has become a vibrant field attracting researchers from mathematics, computer science and statistics. -
Metric Spaces in Pure and Applied Mathematics
Documenta Math. 121 Metric Spaces in Pure and Applied Mathematics A. Dress, K. T. Huber1, V. Moulton2 Received: September 25, 2001 Revised: November 5, 2001 Communicated by Ulf Rehmann Abstract. The close relationship between the theory of quadratic forms and distance analysis has been known for centuries, and the the- ory of metric spaces that formalizes distance analysis and was devel- oped over the last century, has obvious strong relations to quadratic- form theory. In contrast, the first paper that studied metric spaces as such – without trying to study their embeddability into any one of the standard metric spaces nor looking at them as mere ‘presentations’ of the underlying topological space – was, to our knowledge, written in the late sixties by John Isbell. In particular, Isbell showed that in the category whose objects are metric spaces and whose morphisms are non-expansive maps, a unique injective hull exists for every object, he provided an explicit construction of this hull, and he noted that, at least for finite spaces, it comes endowed with an intrinsic polytopal cell structure. In this paper, we discuss Isbell’s construction, we summarize the his- tory of — and some basic questions studied in — phylogenetic analysis, and we explain why and how these two topics are related to each other. Finally, we just mention in passing some intriguing analogies between, on the one hand, a certain stratification of the cone of all metrics de- fined on a finite set X that is based on the combinatorial properties of the polytopal cell structure of Isbell’s injective hulls and, on the other, various stratifications of the cone of positive semi-definite quadratic forms defined on Rn that were introduced by the Russian school in the context of reduction theory. -
Isometric Actions on Spheres with an Orbifold Quotient
ISOMETRIC ACTIONS ON SPHERES WITH AN ORBIFOLD QUOTIENT CLAUDIO GORODSKI AND ALEXANDER LYTCHAK Abstract. We classify representations of compact connected Lie groups whose induced action on the unit sphere has an orbit space isometric to a Riemannian orbifold. 1. Introduction In this paper we classify all orthogonal representations of compact connected groups G on Euclidean unit spheres Sn for which the quotient Sn/G is a Riemannian orbifold. We are going to call such representations infinitesimally polar, since they can be equivalently defined by the condition that slice representations at all non-zero vectors are polar. The interest in such representations is two-fold. On the one hand, one can hope to isolate an interesting class of representations in this way. This class contains all polar representations, which can be defined by the property that the corresponding quotient space Sn/G is an orbifold of constant curvature 1. Polar representations very often play an important and special role in geometric questions concern- ing representations (cf. [PT88, BCO03]), and the class investigated in this paper consists of closest relatives of polar representations. On the other hand, any such quotient has positive curvature and all geodesics in the quotient are closed. Any of these two properties is extremely interesting and in both classes the number of known manifold examples is very limited (cf. [Zil12, Bes78]). We have hoped to obtain new examples of positively curved manifolds and of manifolds with closed geodesics as universal orbi-covering of such spaces. Should the orbifolds be bad one could still hope to obtain new examples of interesting orbifolds. -
Discrete Geometric Homotopy Theory and Critical Values of Metric Spaces Leonard Duane Wilkins [email protected]
View metadata, citation and similar papers at core.ac.uk brought to you by CORE provided by University of Tennessee, Knoxville: Trace University of Tennessee, Knoxville Trace: Tennessee Research and Creative Exchange Doctoral Dissertations Graduate School 5-2011 Discrete Geometric Homotopy Theory and Critical Values of Metric Spaces Leonard Duane Wilkins [email protected] Recommended Citation Wilkins, Leonard Duane, "Discrete Geometric Homotopy Theory and Critical Values of Metric Spaces. " PhD diss., University of Tennessee, 2011. https://trace.tennessee.edu/utk_graddiss/1039 This Dissertation is brought to you for free and open access by the Graduate School at Trace: Tennessee Research and Creative Exchange. It has been accepted for inclusion in Doctoral Dissertations by an authorized administrator of Trace: Tennessee Research and Creative Exchange. For more information, please contact [email protected]. To the Graduate Council: I am submitting herewith a dissertation written by Leonard Duane Wilkins entitled "Discrete Geometric Homotopy Theory and Critical Values of Metric Spaces." I have examined the final electronic copy of this dissertation for form and content and recommend that it be accepted in partial fulfillment of the requirements for the degree of Doctor of Philosophy, with a major in Mathematics. Conrad P. Plaut, Major Professor We have read this dissertation and recommend its acceptance: James Conant, Fernando Schwartz, Michael Guidry Accepted for the Council: Dixie L. Thompson Vice Provost and Dean of the Graduate School (Original signatures are on file with official student records.) To the Graduate Council: I am submitting herewith a dissertation written by Leonard Duane Wilkins entitled \Discrete Geometric Homotopy Theory and Critical Values of Metric Spaces." I have examined the final electronic copy of this dissertation for form and content and recommend that it be accepted in partial fulfillment of the requirements for the degree of Doctor of Philosophy, with a major in Mathematics. -
Helly Groups
HELLY GROUPS JER´ EMIE´ CHALOPIN, VICTOR CHEPOI, ANTHONY GENEVOIS, HIROSHI HIRAI, AND DAMIAN OSAJDA Abstract. Helly graphs are graphs in which every family of pairwise intersecting balls has a non-empty intersection. This is a classical and widely studied class of graphs. In this article we focus on groups acting geometrically on Helly graphs { Helly groups. We provide numerous examples of such groups: all (Gromov) hyperbolic, CAT(0) cubical, finitely presented graph- ical C(4)−T(4) small cancellation groups, and type-preserving uniform lattices in Euclidean buildings of type Cn are Helly; free products of Helly groups with amalgamation over finite subgroups, graph products of Helly groups, some diagram products of Helly groups, some right- angled graphs of Helly groups, and quotients of Helly groups by finite normal subgroups are Helly. We show many properties of Helly groups: biautomaticity, existence of finite dimensional models for classifying spaces for proper actions, contractibility of asymptotic cones, existence of EZ-boundaries, satisfiability of the Farrell-Jones conjecture and of the coarse Baum-Connes conjecture. This leads to new results for some classical families of groups (e.g. for FC-type Artin groups) and to a unified approach to results obtained earlier. Contents 1. Introduction 2 1.1. Motivations and main results 2 1.2. Discussion of consequences of main results 5 1.3. Organization of the article and further results 6 2. Preliminaries 7 2.1. Graphs 7 2.2. Complexes 10 2.3. CAT(0) spaces and Gromov hyperbolicity 11 2.4. Group actions 12 2.5. Hypergraphs (set families) 12 2.6. -
Notes on Metric Spaces
Notes on Metric Spaces These notes introduce the concept of a metric space, which will be an essential notion throughout this course and in others that follow. Some of this material is contained in optional sections of the book, but I will assume none of that and start from scratch. Still, you should check the corresponding sections in the book for a possibly different point of view on a few things. The main idea to have in mind is that a metric space is some kind of generalization of R in the sense that it is some kind of \space" which has a notion of \distance". Having such a \distance" function will allow us to phrase many concepts from real analysis|such as the notions of convergence and continuity|in a more general setting, which (somewhat) surprisingly makes many things actually easier to understand. Metric Spaces Definition 1. A metric on a set X is a function d : X × X ! R such that • d(x; y) ≥ 0 for all x; y 2 X; moreover, d(x; y) = 0 if and only if x = y, • d(x; y) = d(y; x) for all x; y 2 X, and • d(x; y) ≤ d(x; z) + d(z; y) for all x; y; z 2 X. A metric space is a set X together with a metric d on it, and we will use the notation (X; d) for a metric space. Often, if the metric d is clear from context, we will simply denote the metric space (X; d) by X itself. -
Magnitude Homology
Magnitude homology Tom Leinster Edinburgh A theme of this conference so far When introducing a piece of category theory during a talk: 1. apologize; 2. blame John Baez. A theme of this conference so far When introducing a piece of category theory during a talk: 1. apologize; 2. blame John Baez. 1. apologize; 2. blame John Baez. A theme of this conference so far When introducing a piece of category theory during a talk: Plan 1. The idea of magnitude 2. The magnitude of a metric space 3. The idea of magnitude homology 4. The magnitude homology of a metric space 1. The idea of magnitude Size For many types of mathematical object, there is a canonical notion of size. • Sets have cardinality. It satisfies jX [ Y j = jX j + jY j − jX \ Y j jX × Y j = jX j × jY j : n • Subsets of R have volume. It satisfies vol(X [ Y ) = vol(X ) + vol(Y ) − vol(X \ Y ) vol(X × Y ) = vol(X ) × vol(Y ): • Topological spaces have Euler characteristic. It satisfies χ(X [ Y ) = χ(X ) + χ(Y ) − χ(X \ Y ) (under hypotheses) χ(X × Y ) = χ(X ) × χ(Y ): Challenge Find a general definition of `size', including these and other examples. One answer The magnitude of an enriched category. Enriched categories A monoidal category is a category V equipped with a product operation. A category X enriched in V is like an ordinary category, but each HomX(X ; Y ) is now an object of V (instead of a set). linear categories metric spaces categories enriched posets categories monoidal • Vect • Set • ([0; 1]; ≥) categories • (0 ! 1) The magnitude of an enriched category There is a general definition of the magnitude jXj of an enriched category. -
Injective Hulls of Certain Discrete Metric Spaces and Groups
Injective hulls of certain discrete metric spaces and groups Urs Lang∗ July 29, 2011; revised, June 28, 2012 Abstract Injective metric spaces, or absolute 1-Lipschitz retracts, share a number of properties with CAT(0) spaces. In the 1960es, J. R. Isbell showed that every metric space X has an injective hull E(X). Here it is proved that if X is the vertex set of a connected locally finite graph with a uniform stability property of intervals, then E(X) is a locally finite polyhedral complex with n finitely many isometry types of n-cells, isometric to polytopes in l∞, for each n. This applies to a class of finitely generated groups Γ, including all word hyperbolic groups and abelian groups, among others. Then Γ acts properly on E(Γ) by cellular isometries, and the first barycentric subdivision of E(Γ) is a model for the classifying space EΓ for proper actions. If Γ is hyperbolic, E(Γ) is finite dimensional and the action is cocompact. In particular, every hyperbolic group acts properly and cocompactly on a space of non-positive curvature in a weak (but non-coarse) sense. 1 Introduction A metric space Y is called injective if for every metric space B and every 1- Lipschitz map f : A → Y defined on a set A ⊂ B there exists a 1-Lipschitz extension f : B → Y of f. The terminology is in accordance with the notion of an injective object in category theory. Basic examples of injective metric spaces are the real line, all complete R-trees, and l∞(I) for an arbitrary index set I. -
Evolutionary Homology on Coupled Dynamical Systems
Evolutionary homology on coupled dynamical systems Zixuan Cang1, Elizabeth Munch1;2 and Guo-Wei Wei1;3;4 ∗ 1 Department of Mathematics 2Department of Computational Mathematics, Science and Engineering 3 Department of Biochemistry and Molecular Biology 4 Department of Electrical and Computer Engineering Michigan State University, MI 48824, USA February 14, 2018 Abstract Time dependence is a universal phenomenon in nature, and a variety of mathematical models in terms of dynamical systems have been developed to understand the time-dependent behavior of real-world problems. Originally constructed to analyze the topological persistence over spatial scales, persistent homology has rarely been devised for time evolution. We propose the use of a new filtration function for persistent homology which takes as input the adjacent oscillator trajecto- ries of coupled dynamical systems. We also regulate the dynamical system by a weighted graph Laplacian matrix derived from the network of interest, which embeds the topological connectivity of the network into the dynamical system. The resulting topological signatures, which we call evolution- ary homology (EH) barcodes, reveal the topology-function relationship of the network and thus give rise to the quantitative analysis of nodal properties. The proposed EH is applied to protein residue networks for protein thermal fluctuation analysis, rendering the most accurate B-factor prediction of a set of 364 proteins. This work extends the utility of dynamical systems to the quantitative modeling and analysis of realistic physical systems. Contents 1 Introduction 2 2 Methods 4 2.1 Coupled dynamical systems . .4 arXiv:1802.04677v1 [math.AT] 13 Feb 2018 2.1.1 Systems configuration .