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arXiv 1907.13428math.OC
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分数阶微分方程的凸二次Optimization快速求解方法

Fast Solution Methods for Convex Quadratic Optimization of Fractional Differential Equations

Spyridon Pougkakiotis, John W. Pearson, Santolo Leveque, Jacek Gondzio

摘要:

本文提出了一种求解凸二次分数阶微分方程(FDE)约束最优化问题的数值方法,该问题的状态和/或控制变量具有箱形约束。我们开发了一个交替方向法的乘数(ADMM)框架,它使用预处理Krylov子空间求解器所产生的子问题。后者使我们能够解决一系列的偏微分方程(PDE)的最优化问题的框约束,提出了空间-时间域,这是以前的国家的最先进的预处理器的范围。特别是,通过利用强大的广义局部Toeplitz(GLT)序列理论,我们表明,任何现有的GLT结构中存在的问题矩阵被ADMM保存,我们提出了一些预处理的方法,可以在求解器中使用,以证明该方法的一般性。着眼于凸二次规划与时间相关的2维FDE约束,我们推导出多级循环预条件,这可能是嵌入Krylov子空间方法,解决ADMM子问题。FDE的离散化版本涉及大型稠密线性系统。为了克服这一困难,我们设计了一种基于快速傅立叶变换(FFT)的递归线性代数。我们设法保持存储要求线性,相对于网格大小$N$,同时确保Krylov求解器每次迭代的顺序$N \log N$计算复杂性。我们实现了所提出的方法,并证明其可扩展性,通用性和效率,通过一系列的实验在不同的设置FDE最优化问题。

英文摘要:

In this paper, we present numerical methods suitable for solving convex quadratic Fractional Differential Equation (FDE) constrained optimization problems, with box constraints on the state and/or control variables. We develop an Alternating Direction Method of Multipliers (ADMM) framework, which uses preconditioned Krylov subspace solvers for the resulting sub-problems. The latter allows us to tackle a range of Partial Differential Equation (PDE) optimization problems with box constraints, posed on space-time domains, that were previously out of the reach of state-of-the-art preconditioners. In particular, by making use of the powerful Generalized Locally Toeplitz (GLT) sequences theory, we show that any existing GLT structure present in the problem matrices is preserved by ADMM, and we propose some preconditioning methodologies that could be used within the solver, to demonstrate the generality of the approach. Focusing on convex quadratic programs with time-dependent 2-dimensional FDE constraints, we derive multilevel circulant preconditioners, which may be embedded within Krylov subspace methods, for solving the ADMM sub-problems. Discretized versions of FDEs involve large dense linear systems. In order to overcome this difficulty, we design a recursive linear algebra, which is based on the Fast Fourier Transform (FFT). We manage to keep the storage requirements linear, with respect to the grid size $N$, while ensuring an order $N \log N$ computational complexity per iteration of the Krylov solver. We implement the proposed method, and demonstrate its scalability, generality, and efficiency, through a series of experiments over different setups of the FDE optimization problem.

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