Uniqueness and stabilization conjecture for two-orthogonal tensor decompositions

Let WrW_r be the set of tensors in Rn1Rnd\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=mink[d]jknj.N=\min_{k\in[d]}\prod_{j\neq k}n_j.

Two-orthogonal uniqueness and stabilization conjecture. A generic two-orthogonal tensor in Rn1Rnd\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

W1W2WrW_1\subseteq W_2\subseteq\cdots\subseteq W_r\subseteq\cdots

stabilizes exactly at NN:

WN1WN=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.

Sources & referencesView supporting material

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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