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arXiv 2203.00342math.OC
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梯度下降在下受限割线不等式和上误差界条件下是最优的

Gradient Descent Is Optimal Under Lower Restricted Secant Inequality And Upper Error Bound

Charles Guille-Escuret, Adam Ibrahim, Baptiste Goujaud, Ioannis Mitliagkas

AI总结:

针对强凸光滑假设下条件数病态的问题,研究满足下受限割线不等式和上误差界的函数类,通过解析求解性能估计问题,证明梯度下降在该类上对所有一阶算法最优。

摘要:

一阶优化的研究对目标函数所做的假设非常敏感。这些假设引出了复杂度类,它们在最坏情况分析中扮演关键角色,包括算法最优性这一基本概念。近期工作认为,文献中流行的强凸性和光滑性假设会导致条件数的病态定义(Guille-Escuret 等人,2021)。受此结果启发,我们聚焦于满足下受限割线不等式和上误差界的函数类。除了对上述病态行为具有鲁棒性并包含一些非凸函数之外,这对条件还展现出有趣的几何性质。特别是,在该类中插值一组点及其梯度的充要条件可以分解为对每个采样梯度的简单条件。这使得性能估计问题(PEP,Drori 和 Teboulle (2012))能够解析求解,从而得到收敛率的下界,证明梯度下降在这类函数上在所有一阶算法中恰好是最优的。

英文摘要:

The study of first-order optimization is sensitive to the assumptions made on the objective functions. These assumptions induce complexity classes which play a key role in worst-case analysis, including the fundamental concept of algorithm optimality. Recent work argues that strong convexity and smoothness, popular assumptions in literature, lead to a pathological definition of the condition number (Guille-Escuret et al., 2021). Motivated by this result, we focus on the class of functions satisfying a lower restricted secant inequality and an upper error bound. On top of being robust to the aforementioned pathological behavior and including some non-convex functions, this pair of conditions displays interesting geometrical properties. In particular, the necessary and sufficient conditions to interpolate a set of points and their gradients within the class can be separated into simple conditions on each sampled gradient. This allows the performance estimation problem (PEP, Drori and Teboulle (2012)) to be solved analytically, leading to a lower bound on the convergence rate that proves gradient descent to be exactly optimal on this class of functions among all first-order algorithms.

机构、总结、中文摘要均由AI分析而来,可能存在错误,请以论文正文为准。

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