arXivDaily arXiv每日学术速递 周一至周五更新
arXiv 1602.00746math.NAcs.NA
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隐式渐近保方法用于线性输运方程

Implicit Asymptotic Preserving Method for Linear Transport Equations

University of Wisconsin-Madison(威斯康星大学麦迪逊分校);State University of New York at Buffalo(纽约州立大学布法罗分校)

Qin Li, Li Wang

AI总结:

本文提出隐式渐近保方法用于求解辐射传输方程,通过利用不规则矩阵的谱结构构建预条件子,结合空间和角依赖性分解,提升条件数并实现矩阵自由处理,同时设计快速求解器和偶奇奇偶分解方法,实现对称正定矩阵的求解。

摘要:

辐射传输方程的计算成本主要源于两个刚性项:输运项和碰撞算子。前者刚性源于粒子(如光子)以光速运动,后者刚性源于扩散 regime 中的强散射。我们研究该方程的完全隐式方案以应对刚性。隐式处理的主要挑战是空间和速度坐标之间的耦合,需要求解一个大规模的待求逆矩阵,该矩阵也是病态且不一定对称的。我们的主要思想是利用该病态矩阵的谱结构来构建预条件子,结合精妙的空间和角依赖性分解,显著提升条件数并允许矩阵自由处理。我们还设计了快速求解器以提前显式计算该预条件子。同时,我们通过偶奇奇偶分解重构系统,得到一个对称正定矩阵,可通过共轭梯度法求解。这一思想也可应用于原始非对称系统,其求解通过GMRES方法完成。与传统方法,包括通过偶奇分解的渐近保方案和通过扩散合成加速的Krylov迭代方法预条件,进行了定性比较。

英文摘要:

The computation of the radiative transfer equation is expensive mainly due to two stiff terms: the transport term and the collision operator. The stiffness in the former comes from the fact that particles (such as photons) travels at the speed of light, while that in the latter is due to the strong scattering in the diffusive regime. We study the fully implicit scheme for this equation to account for the stiffness. The main challenge in the implicit treatment is the coupling between the spacial and velocity coordinates that requires the large size of the to-be-inverted matrix, which is also ill-conditioned and not necessarily symmetric. Our main idea is to utilize the spectral structure of the ill-conditioned matrix to construct a pre-conditioner, which, along with an exquisite split of the spatial and angular dependence, significantly improve the condition number and allows matrix-free treatment. We also design a fast solver to compute this pre-conditioner explicitly in advance. Meanwhile, we reformulate the system via an even-odd parity, which results in a symmetric and positive definite matrix that can be inverted using conjugate gradient method. This idea can also be implemented to the original non-symmetric system whose inversion is solved by GMRES. A qualitative comparison with the conventional methods, including Krylov iterative method pre-conditioned with diffusive synthetic acceleration and asymptotic preserving scheme via even-odd decomposition, is also discussed.

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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