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MOCCA: Mirrored Convex/Concave Optimization for Nonconvex Composite Functions

机译:MOCCA:非凸复合函数的镜像凸/凹优化

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摘要

Many optimization problems arising in high-dimensional statistics decompose naturally into a sum of several terms, where the individual terms are relatively simple but the composite objective function can only be optimized with iterative algorithms. In this paper, we are interested in optimization problems of the form F(Kx) + G(x), where K is a fixed linear transformation, while F and G are functions that may be nonconvex and/or nondifferentiable. In particular, if either of the terms are nonconvex, existing alternating minimization techniques may fail to converge; other types of existing approaches may instead be unable to handle nondifferentiability. We propose the MOCCA (mirrored convex/concave) algorithm, a primal/dual optimization approach that takes a local convex approximation to each term at every iteration. Inspired by optimization problems arising in computed tomography (CT) imaging, this algorithm can handle a range of nonconvex composite optimization problems, and offers theoretical guarantees for convergence when the overall problem is approximately convex (that is, any concavity in one term is balanced out by convexity in the other term). Empirical results show fast convergence for several structured signal recovery problems.
机译:高维统计中出现的许多优化问题自然分解为多个项的总和,其中各个项相对简单,但复合目标函数只能使用迭代算法进行优化。在本文中,我们对形式为F(Kx)+ G(x)的优化问题感兴趣,其中K是固定的线性变换,而F和G是可能是非凸和/或不可微的函数。特别是,如果任何一项都不是凸的,则现有的交替最小化技术可能无法收敛;相反,其他类型的现有方法可能无法处理不可微性。我们提出了MOCCA(镜像凸/凹)算法,这是一种原始/对偶优化方法,该方法在每次迭代时都对每个项采用局部凸近似。受计算机断层扫描(CT)成像中出现的优化问题的启发,该算法可以处理一系列非凸复合优化问题,并为整体问题近似凸(即平衡一个术语中的任何凹度)提供了理论上的收敛保证。在另一项中由凸度表示)。实验结果表明,对于几种结构化信号恢复问题,其收敛速度很快。

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