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arXiv 1604.04713math.OC
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不动点约束下凸优化的两个随机最优化算法

Two Stochastic Optimization Algorithms for Convex Optimization with Fixed Point Constraints

Hideaki Iiduka

摘要:

针对目标函数以凸函数的期望形式给出,约束集由实Hilbert空间中非扩张映射的不动点集的交集定义的随机规划问题,提出了两种优化算法.这种不动点约束的设置使得能够考虑不能有效地计算到每个约束集上的投影的情况。这两种算法都使用一个凸函数和一个非扩张映射确定的一定的概率过程在每次迭代。一种算法将随机梯度法与Halpern不动点算法混合在一起。另一种是基于随机邻近点法和Halpern不动点算法,可应用于非光滑凸优化。收敛性分析表明,在一定的假设下,任何弱序列聚类点的序列产生的算法几乎肯定属于该问题的解决方案集。收敛速度分析说明了它们的有效性,不动点集上凸优化的数值结果证明了它们的有效性。

英文摘要:

Two optimization algorithms are proposed for solving a stochastic programming problem for which the objective function is given in the form of the expectation of convex functions and the constraint set is defined by the intersection of fixed point sets of nonexpansive mappings in a real Hilbert space. This setting of fixed point constraints enables consideration of the case in which the projection onto each of the constraint sets cannot be computed efficiently. Both algorithms use a convex function and a nonexpansive mapping determined by a certain probabilistic process at each iteration. One algorithm blends a stochastic gradient method with the Halpern fixed point algorithm. The other is based on a stochastic proximal point algorithm and the Halpern fixed point algorithm; it can be applied to nonsmooth convex optimization. Convergence analysis showed that, under certain assumptions, any weak sequential cluster point of the sequence generated by either algorithm almost surely belongs to the solution set of the problem. Convergence rate analysis illustrated their efficiency, and the numerical results of convex optimization over fixed point sets demonstrated their effectiveness.

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