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arXiv · 2301.09826

The Geometry of Rank Drop in a Class of Face-Splitting Matrix Products

Erin Connelly·Sameer Agarwal·Alperen Ergur·Rekha R. Thomas
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Abstract

Given $k \leq 6$ points $(x_i,y_i) \in \mathbb{P}^2 \times \mathbb{P}^2$, we characterize rank deficiency of the $k \times 9$ matrix $Z_k$ with rows $x_i^\top \otimes y_i^\top$ in terms of the geometry of the point configurations $\{x_i\}$ and $\{y_i\}$. While this question comes from computer vision the answer relies on tools from classical algebraic geometry: For $k \leq 5$, the geometry of the rank-drop locus is characterized by cross-ratios and basic (projective) geometry of point configurations. For the case $k=6$ the rank-drop locus is captured by the classical theory of cubic surfaces.

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Erin Connelly, Sameer Agarwal, Alperen Ergur, Rekha R. Thomas. 2023-01-24. The Geometry of Rank Drop in a Class of Face-Splitting Matrix Products. https://arxiv.org/abs/2301.09826

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