Prime-folding characterization of extremal tensors

Let 2n=k=1snpk2\le n=\prod_{k=1}^{s_n}p_k be the prime factorization, with 2p1p2psn2\le p_1\le p_2\le\dots\le p_{s_n}. Consider a tensor TBp1×p2××psn×p1×p2××psn\mathcal{T}\in\mathbb{B}^{p_1\times p_2\times\dots\times p_{s_n}\times p_1\times p_2\times\dots\times p_{s_n}}, where B\mathbb{B} denotes the set of zero-one tensors. Prime-folding conjecture. If T\mathcal{T} satisfies

Tσ=1andT=n,\|\mathcal{T}\|_\sigma=1\quad\text{and}\quad\|\mathcal{T}\|=\sqrt{n},

then T\mathcal{T} can be unfolded to a permutation matrix in Bn×n\mathbb{B}^{n\times n}. This is the remaining structural step toward the preceding characterization conjecture, after reducing to maximum foldings with prime mode dimensions; the paper explicitly says that it cannot currently prove this assertion.

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Primary source

Shengyu Cao, Simai He, Zhening Li and Zhen Wang, “Extreme ratio between spectral and Frobenius norms of nonnegative tensors”, arXiv:2206.07879 (2022).

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