Uniqueness and stabilization conjecture for two-orthogonal tensor decompositions

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Let WrW_r be the set of tensors in Rn1⊗⋯⊗Rnd\mathbb{R}^{n_1}\otimes\cdots\otimes\mathbb{R}^{n_d} admitting a two-orthogonal decomposition with at most rr summands. Let NN be

N=min⁡k∈[d]∏j≠knj.N=\min_{k\in[d]}\prod_{j\neq k}n_j.

Two-orthogonal uniqueness and stabilization conjecture. A generic two-orthogonal tensor in Rn1⊗⋯⊗Rnd\mathbb{R}^{n_1}\otimes\cdots\otimes\mathbb{R}^{n_d} has a unique two-orthogonal decomposition, up to reordering of the summands. In particular, the chain

W1⊆W2⊆⋯⊆Wr⊆⋯W_1\subseteq W_2\subseteq\cdots\subseteq W_r\subseteq\cdots

stabilizes exactly at NN:

WN−1≠WN=WN+1=⋯ .W_{N-1}\neq W_N=W_{N+1}=\cdots.

The conjecture extends the verified uniqueness phenomenon from small cases, including eight summands in (R2)⊗4(\mathbb{R}^2)^{\otimes 4}, and predicts the precise point at which allowing additional summands no longer enlarges the set.

References

Primary source

Alvaro Ribot, Emil Horobet, Anna Seigal and Ettore Teixeira Turatti, “Decomposing tensors via rank-one approximations”, arXiv:2411.15935 (2025).

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