The finite-completion characterization for low-rank matrix patterns

Let Ω\Omega be a matrix-observation pattern, let rr be the target rank, and suppose that every row and column of Ω\Omega contains at least r+1r+1 entries equal to 11. A rank-rr matrix XX is generic if its entries are sufficiently general, and a rank-rr completion of the observations of XX at Ω\Omega is a rank-rr matrix agreeing with XX on those observed entries. Condition ii) of Theorem is the combinatorial condition stated in the source.

Finite-completion conjecture. Without loss of generality, let the number of 11's at every row and column of Ω\Omega be at least r+1r+1. Then a generic rank-rr matrix XX observed at Ω\Omega has finitely many rank-rr completions if and only if Ω\Omega satisfies condition ii) of Theorem.

The conjecture proposes that, after excluding rows and columns with too few observations, condition ii) exactly characterizes finite completability. The source notes that uniquely completable patterns exist beyond the sufficient condition of Theorem, but reports no counterexample to this finite-completion characterization.

Sources & referencesView supporting material

Primary source

Manolis C. Tsakiris, “Low-rank matrix completion theory via Plucker coordinates”, arXiv:2004.12430 (2023).

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