A generalization of Kruskal's theorem on tensor decomposition

TL;DR

This paper introduces a new splitting theorem that generalizes Kruskal's theorem on tensor decomposition, allowing for weaker conditions and certifying uniqueness of tensor decompositions below previous thresholds.

Contribution

It presents a novel proof technique for tensor decomposition uniqueness, extending Kruskal's theorem and related results to broader conditions.

Findings

Generalized Kruskal's theorem using a new proof technique

Established sharp lower bounds on tensor and Waring ranks

Proved new uniqueness results for non-rank tensor decompositions

Abstract

Kruskal's theorem states that a sum of product tensors constitutes a unique tensor rank decomposition if the so-called k-ranks of the product tensors are large. We prove a "splitting theorem" for sets of product tensors, in which the k-rank condition of Kruskal's theorem is weakened to the standard notion of rank, and the conclusion of uniqueness is relaxed to the statement that the set of product tensors splits (i.e. is disconnected as a matroid). Our splitting theorem implies a generalization of Kruskal's theorem. While several extensions of Kruskal's theorem are already present in the literature, all of these use Kruskal's original permutation lemma, and hence still cannot certify uniqueness when the k-ranks are below a certain threshold. Our generalization uses a completely new proof technique, contains many of these extensions, and can certify uniqueness below this threshold. We obtain several other useful results on tensor decompositions as consequences of our splitting theorem. We prove sharp lower bounds on tensor rank and Waring rank, which extend Sylvester's matrix rank inequality to tensors. We also prove novel uniqueness results for non-rank tensor decompositions.