arXiv Machine Learning

Contact Geometry and Covariance Deficits in Volume-Sampled Least Squares

arXiv Machine Learning
Aug 28

When Is the Sharp Covariance Envelope Tight? Feature-Only Geometry for Volume-Sampled Least Squares

The paper extends prior work on volume sampling by providing a Loewner envelope for the centered coefficient covariance in least‑squares regression with a fixed pool of features and responses. It characterizes when this envelope is tight, linking tightness to strict spectral properties of residuals, and introduces a residual‑augmented change of measure to derive a one‑sided slack bound. The results also offer geometric insights at the boundary and demonstrate non‑vacuous certificates through frozen‑feature examples, focusing on conditional centered, full‑Gram‑whitened covariance rather than population generalization.

By Kihun Rhee
arXiv Machine Learning
Sep 10

A Geometric Phase Boundary for Volume-Sampled Linear Readouts

The paper investigates volume‑sampled linear readouts with fixed feature pools and responses, focusing on the randomness introduced solely by subset selection. It establishes a globally sharp Loewner envelope for centered, full‑Gram‑whitened coefficient covariance and characterizes when a positive geometric margin exists versus when it vanishes, using conditions on residual covariance slack and a pairwise Naimark‑complement minor test. The results provide explicit geometric boundaries and conservative certificates for strictness and variance terms in fixed‑query squared loss, offering a design‑specific phase characterization for this randomized linear‑readout primitive.

By Kihun Rhee
arXiv Machine Learning
Sep 4

Restricted Eigenvalues Beyond Gaussian Width: Threshold Occupancy under Heavy Tails

The paper investigates restricted eigenvalue (RE) bounds for norm‑regularized estimators under heavy‑tailed designs. It shows that the previously conjectured sample‑size law based on Gaussian width fails for heavy‑tailed measurements, due to a phenomenon called simultaneous threshold occupancy. The authors provide explicit counterexamples, derive worst‑case sample‑complexity bounds, and compare the behavior of heavy‑tailed versus Gaussian designs on constant‑width polyhedral descent cones.

By Shi Fu, Huibo Xu, Qixin Zhang, Dacheng Tao
arXiv Machine Learning
Sep 25

Sample-Weighted End-to-End Trace-Norm Geometry for Multitask Learning

The paper introduces a sample-weighted trace-norm geometry for multitask learning, focusing on the end-to-end map from task coefficients to input-space predictors. It derives the exact empirical Rademacher complexity for a fixed-radius class and demonstrates that this measure captures orientation and factorization effects that traditional product-based bounds miss. Experiments on 252 held-out comparisons show that weighted joint nuclear regularization consistently improves population excess error over unweighted nuclear regularization and other baselines.

By Mahdi Mohammadigohari