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Homotopy connectivity of Cech complexes of spheres.

Sucharita Mallick ⟨sucharitamallick@ufl.edu⟩

Abstract:

Let Sn be the n-sphere with the geodesic metric and of diameter π. The intrinsic \v{C}ech complex of Sn at scale r is the nerve of all open balls of radius r in Sn. In this talk, we will show how to control the homotopy connectivity of \v{C}ech complexes of spheres at each scale between 0 and π in terms of coverings of spheres. Our upper bound on the connectivity, which is sharp in the case n=1, comes from the chromatic numbers of Borsuk graphs of spheres. Our lower bound is obtained using the conicity (in the sense of Barmak) of \v{C}ech complexes of the sufficiently dense, finite subsets of Sn. Our bounds imply the new result that for n1, the homotopy type of the \v{C}ech complex of Sn at scale r changes infinitely many times as r varies over (0,π). Additionally, we lower bound the homological dimension of \v{C}ech complexes of finite subsets of Sn in terms of their packings. This is joint work with Henry Adams and Ekansh Jauhari.

Scheduled for: 2025-08-13 09:00 AM: Computing Session Talk #4.2 in HUMB 142

Icon: video Webinar

Status: Accepted

Collection: Topology and Computing

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