arXiv:2506.02504cs.LG2025-06NeurIPS

提出新型随机动量方法,显著降低非光滑非凸组合优化的迭代复杂度。

Stochastic Momentum Methods for Non-smooth Non-Convex Finite-Sum Coupled Compositional Optimization

  • 设计专用于非光滑组合优化的随机动量算法,理论可证明收敛性
  • 实现最优迭代复杂度 $O(1/ε^5)$,比现有方法提升一个数量级
  • 适用于深度学习中的约束优化问题,尤其适合处理不平滑目标

有限和耦合组合优化(FCCO)因其耦合结构在众多机器学习问题中具有重要应用。本文针对一类非凸非光滑的FCCO问题,其中外函数为非光滑弱凸或凸,内函数为光滑或弱凸。现有最优方法存在两大局限:(1)在内函数期望利普希茨连续假设下,迭代复杂度高达 $O(1/ε^6)$;(2)依赖传统SGD更新方式,不适用于深度学习。本文主要贡献包括:(i)提出专用于非光滑FCCO的随机动量方法,并提供可证明的收敛性保证;(ii)建立新的最优迭代复杂度 $O(1/ε^5)$。进一步将算法应用于含光滑或弱凸函数不等式约束的非凸优化问题,通过优化平滑铰链惩罚形式,首次实现 $O(1/ε^5)$ 复杂度下求得近似 $ε$-水平的KKT解。三个任务上的实验验证了算法有效性。

原文摘要 · Abstract (English)

Finite-sum Coupled Compositional Optimization (FCCO), characterized by its coupled compositional objective structure, emerges as an important optimization paradigm for addressing a wide range of machine learning problems. In this paper, we focus on a challenging class of non-convex non-smooth FCCO, where the outer functions are non-smooth weakly convex or convex and the inner functions are smooth or weakly convex. Existing state-of-the-art result face two key limitations: (1) a high iteration complexity of $O(1/ε^6)$ under the assumption that the stochastic inner functions are Lipschitz continuous in expectation; (2) reliance on vanilla SGD-type updates, which are not suitable for deep learning applications. Our main contributions are two fold: (i) We propose stochastic momentum methods tailored for non-smooth FCCO that come with provable convergence guarantees; (ii) We establish a new state-of-the-art iteration complexity of $O(1/ε^5)$. Moreover, we apply our algorithms to multiple inequality constrained non-convex optimization problems involving smooth or weakly convex functional inequality constraints. By optimizing a smoothed hinge penalty based formulation, we achieve a new state-of-the-art complexity of $O(1/ε^5)$ for finding an (nearly) $ε$-level KKT solution. Experiments on three tasks demonstrate the effectiveness of the proposed algorithms.

优化算法非凸优化随机方法动量机制

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