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arXiv 1407.7400math.OC
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乘子交替方向法的自等价性

Self Equivalence of the Alternating Direction Method of Multipliers

Ming Yan, Wotao Yin

摘要:

乘法器(ADM或ADMM)的交替方向法将复杂的最优化问题分解为简单得多的子问题。ADM算法通常很短,易于实现,但对于大规模最优化问题表现出(几乎)最先进的性能。为了应用ADM,我们首先将给定的问题公式化为“ADM就绪”形式,因此最终的算法取决于公式。像$\mbox{minimize}_\mathbf{x} u(\mathbf{x}) + v(\mathbf{C}\mathbf{x})$这样的问题有六种不同的“ADM就绪”公式。它们可以是原始或对偶形式,它们的不同之处在于如何引入虚拟变量。对于每个“ADM就绪”公式,ADM可以根据原始变量的更新方式以两种不同的顺序应用。最后,我们得到了十二种不同的ADM算法!它们之间的比较如何?应该选择哪种算法?在本文中,我们表明,许多不同的方式应用ADM是等效的。具体而言,我们表明,ADM适用于原始配方是等效的ADM适用于其拉格朗日对偶; ADM是等效的原始对偶法适用于鞍点制定相同的问题。这些结果是令人惊讶的,因为在ADM的原始和对偶变量似乎是非常不同的对待,和一些以前的工作表现出偏好在一个特定的问题。此外,当两个目标函数之一是二次的,可能受到仿射约束,我们表明,交换的更新顺序的两个原始变量在ADM给出了相同的算法。这些结果确定了几个真正不同的ADM算法的问题,一般有不同形式的子问题,很容易从中挑选一个最计算友好的子问题。

英文摘要:

The alternating direction method of multipliers (ADM or ADMM) breaks a complex optimization problem into much simpler subproblems. The ADM algorithms are typically short and easy to implement yet exhibit (nearly) state-of-the-art performance for large-scale optimization problems. To apply ADM, we first formulate a given problem into the "ADM-ready" form, so the final algorithm depends on the formulation. A problem like $\mbox{minimize}_\mathbf{x} u(\mathbf{x}) + v(\mathbf{C}\mathbf{x})$ has six different "ADM-ready" formulations. They can be in the primal or dual forms, and they differ by how dummy variables are introduced. To each "ADM-ready" formulation, ADM can be applied in two different orders depending on how the primal variables are updated. Finally, we get twelve different ADM algorithms! How do they compare to each other? Which algorithm should one choose? In this paper, we show that many of the different ways of applying ADM are equivalent. Specifically, we show that ADM applied to a primal formulation is equivalent to ADM applied to its Lagrange dual; ADM is equivalent to a primal-dual algorithm applied to the saddle-point formulation of the same problem. These results are surprising since the primal and dual variables in ADM are seemingly treated very differently, and some previous work exhibit preferences in one over the other on specific problems. In addition, when one of the two objective functions is quadratic, possibly subject to an affine constraint, we show that swapping the update order of the two primal variables in ADM gives the same algorithm. These results identify the few truly different ADM algorithms for a problem, which generally have different forms of subproblems from which it is easy to pick one with the most computationally friendly subproblems.

机构、总结、中文摘要均由AI分析而来,可能存在错误,请以论文正文为准。

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