Lower bounds on the homology of Vietoris–Rips complexes of hypercube graphs

Adams, Henry (author), Virk, Žiga (author)

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.

• Language: English
• Keywords: Vietoris–Rips complexes, clique complexes, hypercubes, Betti numbers
• Work type: Article
• Typology: 1.01 - Original Scientific Article
• Organization: FRI - Faculty of Computer and Information Science
• Publication status: Published
• Publication version: Version of Record
• Year: 2024
• Number of pages: 32 str.
• Numbering: Vol. 47, iss. 3, art. 72
• PID: 20.500.12556/RUL-155778
• UDC: 515.1:519.1
• ISSN on article: 0126-6705
• DOI: 10.1007/s40840-024-01663-x
• COBISS.SI-ID: 187729155
• Publication date in RUL: 17.04.2024

Record is a part of a journal

• Title: Bulletin of the Malaysian Mathematical Sciences Society
• Shortened title: Bull. Malays. Math. Sci. Soc.
• Publisher: Springer
• ISSN: 0126-6705
• COBISS.SI-ID: 515781657

Licences

• License: CC BY 4.0, Creative Commons Attribution 4.0 International
• Link: http://creativecommons.org/licenses/by/4.0/
• Description: This is the standard Creative Commons license that gives others maximum freedom to do what they want with the work as long as they credit the author.