4 papers
Gauss-Newton Accuracy and Indefinite Hessians: Uniform Coexistence in Low-Cost Sets
Kihun Rhee, Hanjoon Byun
We study the accuracy of Gauss-Newton curvature in ridge-regularized nonlinear least squares. Under local regularity and persistence of level-set curvature magnitude along an exact…
Exact Calibration and Sharp Risk Geometry for Volume-Sampled Ridge Regression
Kihun Rhee
We study ridge regression from exactly distinct rows of a fixed design. Responses are fixed, and only the subset is random. The determinant law and selected ridge fit share one…
Contact Geometry and Covariance Deficits in Volume-Sampled Least Squares
Kihun Rhee, Hanjoon Byun, Junpyo Seo
We classify when ordinary fixed-size volume sampling followed by unweighted least squares attains its sharp coefficient-covariance ceiling on a fixed design. For a real whitened de…
Confounding Masquerading as Improvement: A Systematic Evaluation of Offline Reinforcement Learning for Stroke Antithrombotic Treatment in a 129,000-Patient Registry
Kihun Rhee
Recent offline reinforcement learning (RL) studies report policies that outperform physician decisions on clinical outcomes. We conduct a systematic, partially crossed evaluation o…