Martin's scaffold duality conjecture for association schemes

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A standard planar scaffold is a weakly connected planar scaffold whose edge weights are among the adjacency matrices A0,…,AcA_0,\dots,A_c of an association scheme. For sequences of such scaffolds, write S†\mathsf{S}^{\dagger} for the dual scaffold, let ∣X∣|X| denote the number of vertices of the association scheme, and let nj,in_{j,i} and ni′n_i' denote the numbers of nodes of Sj,i\mathsf{S}_{j,i} and Si′\mathsf{S}_i', respectively. Let

{Sj,i}i=1kj(1⩽j⩽h),{Si′}i=1k′\{\mathsf{S}_{j,i}\}_{i=1}^{k_j}\quad (1\leqslant j\leqslant h),\qquad \{\mathsf{S}_i'\}_{i=1}^{k'}

be sequences whose scaffolds in each sequence have the same order, and let =1,…,=h,=′ ∈{=,≠}=_1,\dots,=_h,='\,\in\{=,\ne\} and aj,i,bi∈Ca_{j,i},b_i\in\mathbb{C}. Martin's scaffold duality conjecture. If, for every association scheme with d⩾cd\geqslant c classes,

∑i=1kjaj,iSj,i=j0(1⩽j⩽h)⟹∑i=1k′biSi′=′0,\sum_{i=1}^{k_j} a_{j,i}\mathsf{S}_{j,i} =_j0\quad (1\leqslant j\leqslant h)\quad\Longrightarrow\quad\sum_{i=1}^{k'}b_i\mathsf{S}_i'='0,

then, for every association scheme with d⩾cd\geqslant c classes,

∑i=1kjaj,i∣X∣nj,iSj,i†=j0(1⩽j⩽h)⟹∑i=1k′bi∣X∣ni′Si′†=′0.\sum_{i=1}^{k_j}a_{j,i}|X|^{n_{j,i}}\mathsf{S}_{j,i}^{\dagger} =_j0\quad (1\leqslant j\leqslant h)\quad\Longrightarrow\quad\sum_{i=1}^{k'}b_i|X|^{n_i'}\mathsf{S}_i^{\prime\dagger}='0.

This is a strengthened and formalized version of Martin's proposed duality principle: universal implications between equations of scaffolds weighted by adjacency matrices should remain valid after dualizing the scaffolds and interchanging adjacency-matrix and primitive-idempotent weights. Its status is not resolved in the supplied source.

References

Primary source

Xiaoye Liang, Ying-Ying Tan, Hajime Tanaka and Tao Wang, “A duality of scaffolds for translation association schemes”, arXiv:2110.15848 (2021).

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