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arXiv · 2610.29744

On Almost MDS codes holding $(n-k-1)$-designs and an open problem on Witt design

Huakai Wei·Shiyuan Qiang·Shaofang Hong
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Abstract

Let $\mathcal{C}$ be an almost maximum distance separable (AMDS) code over the finite fields with parameters $[n,k,n-k]$ whose minimum-weight codewords support an $(n-k-1)$-$(n,n-k,λ)$ design. We first determine the parameters of the dual code $\mathcal{C}^{\bot}$. We also characterize the design and its complementary design supported by the minimum weight codewords of $\mathcal{C}^{\bot}$. In particular, we present explicit formulas for the weight enumerators of all subset codes of $\mathcal{C}^{\bot}$ with length at least $k+1$. These formulas are completely determined by the cardinality of the subset, the dimension, together with the parameter $λ$, and are independent of the specific choice of subsets. As an application, we answer an open problem posed by Wang, Tang and Ding in 2023 by proving that the $3$-design supported by the minimum-weight codewords in their proposed cyclic dual code is isomorphic to the complementary design of the Witt spherical geometry design.

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Huakai Wei, Shiyuan Qiang, Shaofang Hong. 2026-10-21. On Almost MDS codes holding $(n-k-1)$-designs and an open problem on Witt design. https://arxiv.org/abs/2610.29744

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