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arXiv 1403.5591math.OC
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随机变分不等式问题的最优鲁棒光滑外梯度算法

Optimal robust smoothing extragradient algorithms for stochastic variational inequality problems

Farzad Yousefian, Angelia Nedic, Uday V. Shanbhag

摘要:

考虑紧凸集上映射单调的随机变分不等式问题。我们提出了两个强大的变种的随机超梯度算法来解决这些问题。其中,第一种方案采用迭代平均技术,我们考虑在平均序列中的权重的广义选择。我们的第一个贡献是表明,使用适当的选择这些权重,一个适当定义的间隙函数达到最佳收敛速率${\cal O}\left(\frac{1}{\sqrt{k}}\right)$。在本文的第二部分中,在弱锐度的额外假设下,我们使用利用问题参数的递归规则来更新步长序列。第二个贡献在于表明,采用这样的序列,extragradiation算法具有几乎必然收敛到的解决方案,以及在均方意义上的收敛速度${\cal O}\left(\frac{1}{k}\right)$的问题的解决方案。出于缺乏Lipschitzian参数,在这两个计划中,我们利用局部随机平滑计划。重要的是,通过近似光滑映射,该方案使我们能够估计Lipschitzian参数。每次迭代的平滑参数更新,我们表明收敛到原问题的解决方案,在这两种算法。

英文摘要:

We consider stochastic variational inequality problems where the mapping is monotone over a compact convex set. We present two robust variants of stochastic extragradient algorithms for solving such problems. Of these, the first scheme employs an iterative averaging technique where we consider a generalized choice for the weights in the averaged sequence. Our first contribution is to show that using an appropriate choice for these weights, a suitably defined gap function attains the optimal rate of convergence ${\cal O}\left(\frac{1}{\sqrt{k}}\right)$. In the second part of the paper, under an additional assumption of weak-sharpness, we update the stepsize sequence using a recursive rule that leverages problem parameters. The second contribution lies in showing that employing such a sequence, the extragradient algorithm possesses almost-sure convergence to the solution as well as convergence in a mean-squared sense to the solution of the problem at the rate ${\cal O}\left(\frac{1}{k}\right)$. Motivated by the absence of a Lipschitzian parameter, in both schemes we utilize a locally randomized smoothing scheme. Importantly, by approximating a smooth mapping, this scheme enables us to estimate the Lipschitzian parameter. The smoothing parameter is updated per iteration and we show convergence to the solution of the original problem in both algorithms.

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