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arXiv 2108.10077math.OC
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离散向量值最优化问题的凸松弛

Convex relaxation of discrete vector-valued optimization problems

Christian Clason, Carla Tameling, Benedikt Wirth

摘要:

考虑一类无穷维最优化问题,其中分布向量值变量应几乎处处逐点取值于给定的有限集$\mathcal{M}\subset\mathbb{R}^m$ .这种混合离散-连续问题发生在,例如,拓扑优化或医学成像,并且由于缺乏弱下半连续性而具有挑战性。为了克服这个困难,我们引入了一个凸积分泛函作为正则项,其被积函数具有一个顶点对应于$\mathcal{M}$值的多面体epigra;类似于稀疏正则化中的$L^1$范数,这个“矢量多爆惩罚”促进解决方案与所需的结构,同时允许使用的工具,从凸优化的分析以及数值解的产生的问题。我们证明了正则化问题的适定性,并在一般情况下分析了其解的稳定性。然后,我们说明了三个具体的模型最优化问题的更广泛的利益:最优控制的布洛赫方程,最优控制的弹性变形,和多材料分支运输问题的方法。在前两种情况下,我们得到明确的特征的惩罚和广义导数的一个具体的集合类$\mathcal{M}$。对于第三种情况,我们讨论了一般集合的这些导数的算法计算。这些衍生物,然后使用超线性收敛的半光滑牛顿法应用于一系列正则化最优化问题。我们用数值例子说明了这三个模型问题的行为。

英文摘要:

We consider a class of infinite-dimensional optimization problems in which a distributed vector-valued variable should pointwise almost everywhere take values from a given finite set $\mathcal{M}\subset\mathbb{R}^m$. Such hybrid discrete--continuous problems occur in, e.g., topology optimization or medical imaging and are challenging due to their lack of weak lower semicontinuity. To circumvent this difficulty, we introduce as a regularization term a convex integral functional with an integrand that has a polyhedral epigraph with vertices corresponding to the values of $\mathcal{M}$; similar to the $L^1$ norm in sparse regularization, this "vector multibang penalty" promotes solutions with the desired structure while allowing the use of tools from convex optimization for the analysis as well as the numerical solution of the resulting problem. We show well-posedness of the regularized problem and analyze stability properties of its solution in a general setting. We then illustrate the approach for three specific model optimization problems of broader interest: optimal control of the Bloch equation, optimal control of an elastic deformation, and a multimaterial branched transport problem. In the first two cases, we derive explicit characterizations of the penalty and its generalized derivatives for a concrete class of sets $\mathcal{M}$. For the third case, we discuss the algorithmic computation of these derivatives for general sets. These derivatives are then used in a superlinearly convergent semismooth Newton method applied to a sequence of regularized optimization problems. We illustrate the behavior of this approach for the three model problems with numerical examples.

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