arXiv — Machine Learning · · 3 min read

Structured Proper Loss Geometries for Multiclass Classification: Theory and Controlled Empirical Evaluation

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Computer Science > Machine Learning

arXiv:2606.29471 (cs)
[Submitted on 28 Jun 2026]

Title:Structured Proper Loss Geometries for Multiclass Classification: Theory and Controlled Empirical Evaluation

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Abstract:Strictly proper scoring rules identify the true conditional class distribution at population level, but their curvature can alter optimization and finite-sample behavior. We study three multiclass objectives: a class-aware quadratic Bregman score (CAPM), a strongly convex generator with constrained log-cosh ridges (HPG), and an HPG objective with an annealed probability-margin penalty (APMS). CAPM is treated as a structured instance of established quadratic scoring-rule theory. We derive conditional-regret, curvature, range, and logit-gradient bounds for CAPM and HPG, and prove exact penalty-range and conditional-target displacement bounds for APMS. Controlled five-seed experiments use Digits, Wisconsin breast cancer, and synthetic confusion and long-tail problems under clean labels, symmetric and pair-flip corruption, class imbalance, calibration evaluation, input corruption, and first-order adversarial perturbations. The candidates are close to cross-entropy on clean data and show descriptive gains in some noisy-label cells, but the five-seed comparisons are interpreted descriptively rather than as significance evidence. The selected noisy-label baselines perform better on Digits with 40% symmetric label noise, and explicit prior-adjustment methods perform better in the 30:1 synthetic long-tail experiment. Ablations do not show a consistent benefit from the candidate-specific graph, ridge, or margin components. The mathematical analysis establishes the stated properties, and the experiments delimit the empirical evidence; together they do not support a claim of general superiority.
Subjects: Machine Learning (cs.LG); Numerical Analysis (math.NA)
Cite as: arXiv:2606.29471 [cs.LG]
  (or arXiv:2606.29471v1 [cs.LG] for this version)
  https://doi.org/10.48550/arXiv.2606.29471
arXiv-issued DOI via DataCite (pending registration)

Submission history

From: Soumyadip Sarkar [view email]
[v1] Sun, 28 Jun 2026 15:57:59 UTC (206 KB)
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