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Abstract: We consider persistent homology obtained by applying homology to the open Rips filtration of a compact metric space $(X, d)$. We show that each decrease in zero-dimensional persistence and each increase in one-dimensional persistence is induced by local minima of the distance function $d$ When $d$ attains local minimum at only finitely many pairs of points, we prove that each above mentioned change in persistence is induced by a specific critical edge in Rips complexes, which represents a local minimum of $d$. We use this fact to develop a theory (including interpretation) of critical edges of persistence. The obtained results include upper bounds for the rank of one-dimensional persistence and a corresponding reconstruction result. Of potential computational interest is a simple geometric criterion recognizing local minima of $d$ that induce a change in persistence. We conclude with a proof that each locally isolated minimum of $d$ can be detected through persistent homology with selective Rips complexes. The results of this paper offer the first interpretation of critical scales of persistent homology (obtained via Rips complexes) for general compact metric spaces.
Keywords: persistent homology, Rips complex, critical simplex, reconstruction result
Published in DiRROS: 10.04.2024; Views: 58; Downloads: 32
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Abstract: We provide novel lower bounds on the Betti numbers of Vietoris-Rips complexes of hypercube graphs of all dimensions, and at all scales. In more detail, let $Q_n$ be the vertex set of $2^n$ vertices in the $n$-dimensional hypercube graph, equipped with the shortest path metric. Let ${\rm VR}(Q_n;r)$ be its Vietoris-Rips complex at scale parameter $r \ge 0$, which has $Q_n$ as its vertex set, and all subsets of diameter at most $r$ as its simplices. For integers $r < r'$ the inclusion ${\rm VR}(Q_n;r) \hookrightarrow {\rm VR}(Q_n;r')$ is nullhomotopic, meaning no persistent homology bars have length longer than one, and we therefore focus attention on the individual spaces ${\rm VR}(Q_n;r)$. We provide lower bounds on the ranks of homology groups of ${\rm VR}(Q_n;r)$. For example, using cross-polytopal generators, we prove that the rank of $H_{2^r-1}({\rm VR}(Q_n;r))$ is at least $2^{n-(r+1)}\binom{n}{r+1}$. We also prove a version of homology propagation: if $q\ge 1$ and if $p$ is the smallest integer for which ${\rm rank} H_q({\rm VR}(Q_p;r)) \neq 0$, then ${\rm rank} H_q({\rm VR}(Q_n;r)) \ge \sum_{i=p}^n 2^{i-p} \binom{i-1}{p-1} \cdot {\rm rank} H_q({\rm VR}(Q_p;r))$ for all $n \ge p$. When $r \le 3$, this result and variants thereof provide tight lower bounds on the rank of $H_q({\rm VR}(Q_n;r))$ for all $n$, and for each $r \ge 4$ we produce novel lower bounds on the ranks of homology groups. Furthermore, we show that for each $r\ge 2$, the homology groups of ${\rm VR}(Q_n;r)$ for $n \ge 2r+1$ contain propagated homology not induced by the initial cross-polytopal generators.
Keywords: Vietoris–Rips complexes, clique complexes, hypercubes, Betti numbers
Published in DiRROS: 05.03.2024; Views: 135; Downloads: 40
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