3 papers
math.CO2026
Twisted primitive group association schemes
Akihiro Higashitani, Masanari Kamiya, Hirotake Kurihara
We give results on the question of whether the intersection numbers of a primitive group association scheme determine it up to combinatorial isomorphism. For $G=\operatorname{PSL}(…
math.CO2026
Imprimitive association schemes and elimination theory
Akihiro Higashitani, Hirotake Kurihara
We prove that a commutative association scheme is imprimitive if and only if it admits a multivariate - or -polynomial structure with respect to an elimination-type monomial…
math.AG2026
Polyptych lattices and marked chain-order polytopes
Naoki Fujita, Akihiro Higashitani
The theory of polyptych lattices is a framework to obtain a family of toric degenerations whose polytopes are related by piecewise-linear transformations. It can be regarded as a g…