arXiv:2605.14373cs.LGcs.AI2026-05中稿 · ICML

提出一种高效稳定的零阶优化方法,用历史梯度提升性能。

Turning Stale Gradients into Stable Gradients: Coherent Coordinate Descent with Implicit Landscape Smoothing for Lightweight Zeroth-Order Optimization

论文配图:Turning Stale Gradients into Stable Gradients: Coherent Coordinate Descent with Implicit Landscape Smoothing for Lightweight Zeroth-Order Optimization
图 1 · 摘自论文原文
  • 基于坐标下降与梯度相干性,实现确定性更新。
  • 每步仅需一次查询,收敛损失更低且更稳定。
  • 适合设备端轻量级优化,尤其参数量大的模型。

零阶(ZO)优化在无法使用反向传播的场景中至关重要,如内存受限的设备端学习和黑盒优化。现有方法存在明显权衡:标准有限差分法样本效率低,随机子空间方法因随机估计导致方差高。本文提出一致坐标下降(CoCD),一种确定性、样本高效且预算感知的零阶优化器。理论上,我们定义了梯度相干性,并证明CoCD等价于带‘热启动’的块循环坐标下降(BCCD),将历史(过时)梯度转化为计算资产。该机制使每步查询复杂度为 $O(1)$,同时保持全局下降方向。此外,我们推导出误差界,揭示一个反直觉现象:更大的有限差分步长能通过降低有效光滑常数,对优化景观产生隐式平滑作用,从而提升收敛稳定性。在包含MLP、CNN和ResNet(最大达270k参数)的实验中,CoCD显著优于BCCD,在样本效率和收敛损失/精度上表现更优,且相比随机化零阶方法更具稳定性。结果表明,确定性、结构感知的更新是轻量级零阶优化的更优选择。

原文摘要 · Abstract (English)

Zeroth-Order (ZO) optimization is pivotal for scenarios where backpropagation is unavailable, such as memory-constrained on-device learning and black-box optimization. However, existing methods face a stark trade-off: they are either sample-inefficient (e.g., standard finite differences) or suffer from high variance due to randomized estimation (e.g., random subspace methods). In this work, we propose Coherent Coordinate Descent (CoCD), a deterministic, sample-efficient, and budget-aware ZO optimizer. Theoretically, we formalize the notion of gradient coherence and demonstrate that CoCD is equivalent to Block Cyclic Coordinate Descent (BCCD) with ``warm starts,'' effectively converting historical (stale) gradients from a liability into a computational asset. This mechanism enables $O(1)$ query complexity per step while maintaining global descent directions. Furthermore, we derive error bounds revealing a counter-intuitive insight: larger finite-difference step sizes can induce an implicit smoothing effect on the optimization landscape by reducing the effective smoothness constant, thereby improving convergence stability. Experiments on MLP, CNN, and ResNet architectures (up to 270k parameters) demonstrate that CoCD significantly outperforms BCCD in terms of sample efficiency and convergence loss/accuracy, and exhibits superior stability over randomized ZO methods. Our results suggest that deterministic, structure-aware updates offer a superior alternative to randomization for lightweight ZO optimization.

零阶优化坐标下降轻量级学习确定性方法

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