Grid homotopic curve shortening approximates affine curve-shortening flow

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Let δ\delta be an initial curve, and let γ0\gamma_0 be the shortest curve homotopic to it among curves avoiding the obstacle set Pn=(Z/n)2P_n=(\mathbb Z/n)^2. For t>0t>0, write δ′=δ(t)\delta'=\delta(t) for the curve obtained from δ\delta under affine curve-shortening flow (ACSF), whenever it is defined. Let cg≈1.6c_{\mathrm g}\approx 1.6 be a constant, set

m=⌊cgtn4/3⌋,m=\lfloor c_{\mathrm g}tn^{4/3}\rfloor,

and let γm=HCS⁡P(m)(γ0)\gamma_m=\operatorname{\mathrm HCS}_P^{(m)}(\gamma_0) be the result of mm homotopic curve-shortening iterations. Grid approximation conjecture. There exists a constant cg≈1.6c_{\mathrm g}\approx 1.6 such that, for every fixed t>0t>0 for which δ′\delta' is defined, the Fr\e9chet distance between γm\gamma_m and δ′\delta' tends to 00 as n→∞n\to\infty. This conjecture formalizes the experimentally observed connection between HCS on increasingly fine uniform grids and ACSF, generalizing the cited grid-peeling conjecture; its resolution is not given in the source.

References

Primary source

Sergey Avvakumov and Gabriel Nivasch, “Homotopic curve shortening and the affine curve-shortening flow”, arXiv:1909.00263 (2022).

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