ResearchResearch paperTraining & Scaling · Efficiency & Inference · Computer Vision1 source · Oct 7, 2026

Gauss-Newton Accuracy and Indefinite Hessians: Uniform Coexistence in Low-Cost Sets

We study the accuracy of Gauss-Newton curvature in ridge-regularized nonlinear least squares.

Key points

  • Under local regularity and persistence of level-set curvature magnitude along an exact-fit section, we prove uniform coexistence of two curvature regimes.
  • Global minimizers exist, and every global minimizer has relative Hessian error below $(1+\sqrt2)/8$, while the same low-cost set contains a point with an indefinite Hessian and relative error at least $15/8$.
  • A pointwise certificate based on the current prediction level set controls the normal, mixed, and tangent parts of the Hessian correction.
  • We prove a sharp relative-error bound over the stated pointwise class when the prediction map and ridge vary.

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