Polygon recutting singularity position conjecture

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Let m∈Zm\in\mathbb{Z} and let z~\tilde z be an mm-closed polygon recutting lattice map, meaning z~i,j=z~i+m,j−m\tilde z_{i,j}=\tilde z_{i+m,j-m} for all i,ji,j. Assume z~i,0=0\tilde z_{i,0}=0 for all i∈2Zi\in 2\mathbb{Z}, define yi=z~2i+1,1y_i=\tilde z_{2i+1,1} and ϱi=ℓ2i=ℓ2i+1\varrho_i=\ell_{2i}=\ell_{2i+1}, and let Ik\mathcal I_k be the set of kk-subsets of {0,1,…,m−1}\{0,1,\dots,m-1\}. Assume polygon recutting TT can be applied to z~\tilde z at least m−1m-1 times. Polygon recutting singularity position conjecture. If m∈2Z+1m\in 2\mathbb{Z}+1 and k=(m−1)/2k=(m-1)/2, then, for every i∈2Z+1i\in 2\mathbb{Z}+1, z~i,m\tilde z_{i,m} equals the stated ratio of sums over Ik\mathcal I_k; if m∈2Zm\in 2\mathbb{Z} and k=m/2k=m/2, then, for every i∈2Zi\in 2\mathbb{Z}, z~i,m\tilde z_{i,m} equals the stated ratio of sums over Ik−1\mathcal I_{k-1} and Ik\mathcal I_k. Explicitly, the odd case is

z~i,m=(−1)k∑I∈Ik[∏r∈I(−1)r∏r∉Iyr∏r,s∈I,r<s(ϱr2−ϱs2)∏r,s∉I,r<s(ϱr2−ϱs2)]∑I∈Ik[∏r∈I(−1)r∏r∈Iyr∏r,s∈I,r<s(ϱr2−ϱs2)∏r,s∉I,r<s(ϱr2−ϱs2)].\tilde z_{i,m}=(-1)^k\frac{\sum\limits_{I\in\mathcal I_k}\left[\prod\limits_{r\in I}(-1)^r\prod\limits_{r\notin I}y_r\prod\limits_{r,s\in I,r<s}(\varrho_r^2-\varrho_s^2)\prod\limits_{r,s\notin I,r<s}(\varrho_r^2-\varrho_s^2)\right]}{\sum\limits_{I\in\mathcal I_k}\left[\prod\limits_{r\in I}(-1)^r\prod\limits_{r\in I}y_r\prod\limits_{r,s\in I,r<s}(\varrho_r^2-\varrho_s^2)\prod\limits_{r,s\notin I,r<s}(\varrho_r^2-\varrho_s^2)\right]}.

The even case is

z~i,m=(−1)k+1∑I∈Ik−1[∏r∈I(−1)rϱr2∏r∉Iyr∏r,s∈I,r<s(ϱr2−ϱs2)∏r,s∉I,r<s(ϱr2−ϱs2)]∑I∈Ik[∏r∈I(−1)rϱr2∏r∈Iyr∏r,s∈I,r<s(ϱr2−ϱs2)∏r,s∉I,r<s(ϱr2−ϱs2)].\tilde z_{i,m}=(-1)^{k+1}\frac{\sum\limits_{I\in\mathcal I_{k-1}}\left[\prod\limits_{r\in I}(-1)^r\varrho_r^2\prod\limits_{r\notin I}y_r\prod\limits_{r,s\in I,r<s}(\varrho_r^2-\varrho_s^2)\prod\limits_{r,s\notin I,r<s}(\varrho_r^2-\varrho_s^2)\right]}{\sum\limits_{I\in\mathcal I_k}\left[\prod\limits_{r\in I}(-1)^r\varrho_r^2\prod\limits_{r\in I}y_r\prod\limits_{r,s\in I,r<s}(\varrho_r^2-\varrho_s^2)\prod\limits_{r,s\notin I,r<s}(\varrho_r^2-\varrho_s^2)\right]}.

The conjecture gives an explicit formula for the position of the singularity following the known polygon recutting Devron phenomenon; the source does not state whether these formulas have been proved.

References

Primary source

Niklas Christoph Affolter, Béatrice de Tilière and Paul Melotti, “The Schwarzian octahedron recurrence (dSKP equation) II: geometric systems”, arXiv:2208.00244 (2024).

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