Modularity conjecture for uniacute spherical codes

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Let α,β∈(0,1)\alpha,\beta \in (0,1) and let L⊆[−1,−β]∪{α}L \subseteq [-1,-\beta]\cup\{\alpha\} with α∈L\alpha \in L. An LL-code is a finite set of unit vectors in Euclidean space whose pairwise inner products lie in LL; write NL(d)N_L(d) for the maximum size of an LL-code in Rd\mathbb{R}^d. A modular LL-code is one for which, after possibly reordering its vectors, its Gram matrix MCM_C dominates a template in the positive-semidefinite order, and write NLmod(d)N_L^{\mathrm{mod}}(d) for the maximum size of a modular LL-code in Rd\mathbb{R}^d. Modularity conjecture. For fixed α\alpha, β\beta, and LL as above,

NL(d)=NLmod(d)+o(d)as d→∞.N_L(d)=N_L^{\mathrm{mod}}(d)+o(d)\quad\text{as }d\to\infty.

The conjecture asserts that modular codes capture the asymptotically maximal size of uniacute spherical codes, up to a sublinear error. The paper notes that all known tight uniacute spherical codes in high dimensions arise from modular codes, but no resolution is given here.

References

Primary source

Saba Lepsveridze, Aleksandre Saatashvili and Yufei Zhao, “Uniacute Spherical Codes”, arXiv:2311.17734 (2023).

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