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arXiv 1709.07085math.OC
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一种基于群集的分布式随机最优化方法

A Flocking-based Approach for Distributed Stochastic Optimization

Shi Pu, Alfredo Garcia

摘要:

近年来,云计算的范例已经作为利用分布式(联网)计算资源的计算架构而出现。在本文中,我们考虑一个分布式计算算法方案的随机最优化,它依赖于适度的处理器之间的通信要求,最重要的是,不需要同步。具体来说,我们分析了一个计划与$N>1$独立的线程实现每个随机梯度算法。这些线通过梯度的扰动(具有吸引力和排斥力)以类似于自然界中发现的具有温和通信要求的群集、群集和其他群组形成的数学模型的方式耦合。当目标函数是凸的,我们表明,分布式随机最优化的一个群集的方法提供了一个降噪效果类似的集中式随机梯度算法的基础上,平均$N$梯度样本在每一步。群集的分布式本质使其成为一种吸引人的计算替代方案。我们表明,当收集$N$样本和同步所需的时间相关的开销是不可忽略的,植绒实现优于集中的随机梯度算法的基础上,平均$N$梯度样本在每一步。当目标函数不是凸函数时,基于群集的方法似乎更适合于逃避局部最优解,这是由于排斥力在候选解集合中强制执行一定程度的多样性。在这里,我们再次表明,降噪效果是类似的集中式随机梯度算法的基础上的平均值的$N$梯度样本在每一步。

英文摘要:

In recent years, the paradigm of cloud computing has emerged as an architecture for computing that makes use of distributed (networked) computing resources. In this paper, we consider a distributed computing algorithmic scheme for stochastic optimization which relies on modest communication requirements amongst processors and most importantly, does not require synchronization. Specifically, we analyze a scheme with $N>1$ independent threads implementing each a stochastic gradient algorithm. The threads are coupled via a perturbation of the gradient (with attractive and repulsive forces) in a similar manner to mathematical models of flocking, swarming and other group formations found in nature with mild communication requirements. When the objective function is convex, we show that a flocking-like approach for distributed stochastic optimization provides a noise reduction effect similar to that of a centralized stochastic gradient algorithm based upon the average of $N$ gradient samples at each step. The distributed nature of flocking makes it an appealing computational alternative. We show that when the overhead related to the time needed to gather $N$ samples and synchronization is not negligible, the flocking implementation outperforms a centralized stochastic gradient algorithm based upon the average of $N$ gradient samples at each step. When the objective function is not convex, the flocking-based approach seems better suited to escape locally optimal solutions due to the repulsive force which enforces a certain level of diversity in the set of candidate solutions. Here again, we show that the noise reduction effect is similar to that associated to the centralized stochastic gradient algorithm based upon the average of $N$ gradient samples at each step.

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