提出新方法解决多专家学习拒答中的优化难题,稳定性显著提升。
Beyond Augmented-Action Surrogates for Multi-Expert Learning-to-Defer
- 分离分类器与专家路由头,避免传统方法的优化病灶
- 专家池扩大时仍稳定,罕见专家不被淹没,性能优于单一分类器
- 首个专家数增长但常数不变的风险保证,适合大规模专家系统
学习拒答(L2D)系统在每个输入上决定是否自主预测或转交至多个可用专家。现有主流方法将 $K$ 类与 $J$ 个专家统一为 $(K{+}J)$ 动作空间联合训练,但后续改进仍存在目标扭曲、梯度放大、赢家通吃抑制、集合质量坍缩或类别-专家耦合等优化层面问题,即使在统计一致性下依然存在。本文跳出该框架,提出解耦代理:使用 softmax 分类头和独立 sigmoid 头对应每个专家,贴合问题本质结构。理论证明每样本更新坐标独立,类别-专家海森块恒为零,并建立过量风险界,校准常数为 $\ ext{max}\\{2\sqrt{2},\sqrt{2J/λ}\\}$ ——据我们所知,首个在专家数量增长时,常数不随专家池增大而上升的多专家 L2D 理论保证(当每专家权重固定)。在可控合成数据与 CIFAR-10、CIFAR-10H、Covertype 上,该方法是唯一在专家池扩张时仍保持稳定的模型,能保留稀有专家,且在所有真实数据集上均优于独立分类器。
原文摘要 · Abstract (English)
A learning-to-defer (L2D) system decides, for each input, whether to predict on its own or to hand it to one of several available experts. The very well established recipe trains classifier and router jointly by treating the $K$ classes and $J$ experts as competing actions in one shared $(K{+}J)$-action geometry. Subsequent work has proposed a series of incremental fixes within this geometry; we show that each still suffers, to varying severity, from an optimization-level pathology (target distortion, gradient amplification, winner-take-all starvation, set-mass collapse, or class-expert coupling) even under statistical consistency. We step outside the augmented-action family entirely and propose a decoupled surrogate: a softmax classifier head and an independent sigmoid head per expert, mirroring the two natural objects of the problem. We show that per-sample updates are then coordinatewise and the class-expert Hessian block is identically zero, and prove an excess-risk bound with calibration constant $\max\{2\sqrt{2},\sqrt{2J/λ}\}$ -- to our knowledge the first multi-expert L2D guarantee whose constant does not grow with the expert pool when the per-expert weight is held fixed. On controlled synthetic studies and on CIFAR-10, CIFAR-10H, and Covertype, it is the only method in our comparison that remains stable as the expert pool grows, preserves rare specialists, and improves over a standalone classifier on every real-data benchmark.
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