Lower semicontinuity of the homotopy type of Vietoris-Rips complexes

Let XX be a compact metric space, let rR>0r\in\mathbb{R}_{>0}, and let VRr(X)\mathrm{VR}_r(X) denote the Vietoris-Rips complex at scale rr.

Lower semicontinuity conjecture. The complex VRr(X)\mathrm{VR}_r(X) is homotopy equivalent to VRrε(X)\mathrm{VR}_{r-\varepsilon}(X) whenever ε>0\varepsilon>0 is sufficiently small.

The paper explicitly labels this conjecture as false and provides a counterexample immediately afterward. Thus the proposed lower semicontinuity statement does not hold for all compact metric spaces.

Sources & referencesView supporting material

Primary source

Sunhyuk Lim, Facundo Memoli and Osman Berat Okutan, “Vietoris-Rips Persistent Homology, Injective Metric Spaces, and The Filling Radius”, arXiv:2001.07588 (2024).

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