Diameter-preservation conjecture for the Vietoris–Rips thickening retraction

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Let k≥1k\geq 1, let rr satisfy

2π(k−1)2k−1≤r<2πk2k+1,\frac{2\pi(k-1)}{2k-1}\leq r<\frac{2\pi k}{2k+1},

let μ∈VRm(S1;r)\mu\in\mathrm{VR}^m(S^1;r), and let ι\iota map the boundary of the Barvinok–Novik orbitope B2k\mathcal{B}_{2k} into the Vietoris–Rips metric thickening. Let pp be radial projection to ∂B2k\partial\mathcal{B}_{2k} and let SM2k\mathrm{SM}_{2k} be the spherical moment map. Diameter-preservation conjecture.

diam⁡(supp⁡(μ))=diam⁡(supp⁡(μ)∪supp⁡(ι∘p∘SM2k(μ))).\operatorname{diam}(\operatorname{supp}(\mu))=\operatorname{diam}\bigl(\operatorname{supp}(\mu)\cup\operatorname{supp}(\iota\circ p\circ\mathrm{SM}_{2k}(\mu))\bigr).

This would control the effect of the proposed retraction on supports of measures and is intended to help show that p∘SM2kp\circ\mathrm{SM}_{2k} and ι\iota are homotopy inverses. The supplied text does not state a resolution.

References

Primary source

Henry Adams, Johnathan Bush and Florian Frick, “Metric Thickenings, Borsuk-Ulam Theorems, and Orbitopes”, arXiv:1907.06276 (2019).

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