论文标题

在组成约束下的随机成分梯度下降

Stochastic Compositional Gradient Descent under Compositional Constraints

论文作者

Thomdapu, Srujan Teja, Harshvardhan, Rajawat, Ketan

论文摘要

这项研究限制了随机函数是凸的,并表示为随机函数的组成,限制了随机优化问题。问题是在公平分类,公平回归和排队系统设计的背景下引起的。特别令人感兴趣的是甲骨文提供组成函数的随机梯度的大规模设置,目标是通过对Oracle的呼叫数量最少来解决问题。由于组成形式,Oracle提供的随机梯度不会产生目标或约束梯度的无偏估计。取而代之的是,我们通过跟踪内部函数评估来构建近似梯度,从而导致准距离鞍点算法。我们证明,所提出的算法几乎可以肯定地找到最佳且可行的解决方案。我们进一步确定所提出的算法需要$ \ MATHCAL {O}(1/ε^4)$数据样本才能获得$ε$ - appproximate的最佳点,同时还可以确保违反零约束。结果与无约束问题的随机组成梯度下降法的样品复杂性相匹配,并在受约束设置的最著名样本复杂性结果上得到了改善。在公平分类和公平回归问题上测试了所提出的算法的功效。数值结果表明,根据收敛速率,所提出的算法优于最新算法。

This work studies constrained stochastic optimization problems where the objective and constraint functions are convex and expressed as compositions of stochastic functions. The problem arises in the context of fair classification, fair regression, and the design of queuing systems. Of particular interest is the large-scale setting where an oracle provides the stochastic gradients of the constituent functions, and the goal is to solve the problem with a minimal number of calls to the oracle. Owing to the compositional form, the stochastic gradients provided by the oracle do not yield unbiased estimates of the objective or constraint gradients. Instead, we construct approximate gradients by tracking the inner function evaluations, resulting in a quasi-gradient saddle point algorithm. We prove that the proposed algorithm is guaranteed to find the optimal and feasible solution almost surely. We further establish that the proposed algorithm requires $\mathcal{O}(1/ε^4)$ data samples in order to obtain an $ε$-approximate optimal point while also ensuring zero constraint violation. The result matches the sample complexity of the stochastic compositional gradient descent method for unconstrained problems and improves upon the best-known sample complexity results for the constrained settings. The efficacy of the proposed algorithm is tested on both fair classification and fair regression problems. The numerical results show that the proposed algorithm outperforms the state-of-the-art algorithms in terms of the convergence rate.

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