Low-rank matrix completion (LRMC) problems arise in a wide variety of
applications. Previous theory mainly provides conditions for completion under
missing-at-random samplings. This paper studies deterministic conditions for
completion. An incomplete $d \times N$ matrix is finitely rank-$r$ completable
if there are at most finitely many rank-$r$ matrices that agree with all its
observed entries. Finite completability is the tipping point in LRMC, as a few
additional samples of a finitely completable matrix guarantee its unique
completability. The main contribution of this paper is a deterministic sampling
condition for finite completability. We use this to also derive deterministic
sampling conditions for unique completability that can be efficiently verified.
We also show that under uniform random sampling schemes, these conditions are
satisfied with high probability if $O(\max\{r,\log d\})$ entries per column are
observed. These findings have several implications on LRMC regarding lower
bounds, sample and computational complexity, the role of coherence, adaptive
settings and the validation of any completion algorithm. We complement our
theoretical results with experiments that support our findings and motivate
future analysis of uncharted sampling regimes.

本文研究低秩矩阵完成问题，提出了一种用于确定有限可完成性的确定性采样条件，展示了在随机采样下，以 O（max（r，log d））的采样数完成矩阵的特定条件可以高概率满足，并探讨了该发现对 LRMC 的意义与应用。