2015/03/31 by Michał Adamaszek, Michal Adamaszek, Henry Adams · 1 citation
Computer Science · Mathematics · #CW complex #Combinatorics #Contractible space #Fibration #Geometry #Great circle #Homotopy #Homotopy and Cohomology in Algebraic Topology #Homotopy group #Homotopy sphere #Mathematical analysis #Mathematics #Metric space #Pure mathematics #Simplicial complex #Singular homology #Topological and Geometric Data Analysis #Topology (electrical circuits) #Winding number #cs.CG #math.AT #math.CO #math.MG
paper · pdf · doi:10.2140/pjm.2017.290.1
published as Pacific Journal of Mathematics 290-1 (2017), 1-40 · Final version
arxiv created 2017/02/05 · openalex publication_date 2017/07/07 · arxiv updated 2020/11/03 · openalex created_date 2020/11/23 · openalex updated_date 2026/08/05
Given a metric space X and a distance threshold r>0, the Vietoris-Rips simplicial complex has as its simplices the finite subsets of X of diameter less than r. A theorem of Jean-Claude Hausmann states that if X is a Riemannian manifold and r is sufficiently small, then the Vietoris-Rips complex is homotopy equivalent to the original manifold. Little is known about the behavior of Vietoris-Rips complexes for larger values of r, even though these complexes arise naturally in applications using persistent homology. We show that as r increases, the Vietoris-Rips complex of the circle obtains the homotopy types of the circle, the 3-sphere, the 5-sphere, the 7-sphere, ..., until finally it is contractible. As our main tool we introduce a directed graph invariant, the winding fraction, which in some sense is dual to the circular chromatic number. Using the winding fraction we classify the homotopy types of the Vietoris-Rips complex of an arbitrary (possibly infinite) subset of the circle, and we study the expected homotopy type of the Vietoris-Rips complex of a uniformly random sample from the circle. Moreover, we show that as the distance parameter increases, the ambient Cech complex of the circle also obtains the homotopy types of the circle, the 3-sphere, the 5-sphere, the 7-sphere, ..., until finally it is contractible.