改进了指数移动平均,让估计值更稳定可靠。
An Exponential Averaging Process with Strong Convergence Properties
- 提出p-EMA,让近期数据权重随时间递减至零。
- 在弱自相关条件下,证明了该方法具有强收敛性。
- 适用于SGD自适应步长控制,提升优化稳定性。
平滑是通过噪声观测获取稳定、去噪估计的基本方法。在随机动力系统轨迹上的观测尤为关键。一种常用方法是指数移动平均(EMA),其对观测赋予随年龄呈指数衰减的权重,使新数据权重更大。然而,EMA缺乏强随机收敛性,因其对最新观测的权重恒定,导致平均量中的噪声无法趋于零。本文提出一种EMA改进方法——p-EMA,其对最近观测的权重以亚调和速率递减至零。在对底层随机动力系统自相关性施加弱假设的前提下,我们给出了该类平均的随机收敛保证。此外,我们讨论了这些结果对近期提出的基于p-EMA的随机梯度下降(SGD)自适应步长控制方法的启示。
原文摘要 · Abstract (English)
Averaging, or smoothing, is a fundamental approach to obtain stable, de-noised estimates from noisy observations. In certain scenarios, observations made along trajectories of random dynamical systems are of particular interest. One popular smoothing technique for such a scenario is exponential moving averaging (EMA), which assigns observations a weight that decreases exponentially in their age, thus giving younger observations a larger weight. However, EMA fails to enjoy strong stochastic convergence properties, which stems from the fact that the weight assigned to the youngest observation is constant over time, preventing the noise in the averaged quantity from decreasing to zero. In this work, we consider an adaptation to EMA, which we call $p$-EMA, where the weights assigned to the last observations decrease to zero at a subharmonic rate. We provide stochastic convergence guarantees for this kind of averaging under mild assumptions on the autocorrelations of the underlying random dynamical system. We further discuss the implications of our results for a recently introduced adaptive step size control for Stochastic Gradient Descent (SGD), which uses $p$-EMA for averaging noisy observations.
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