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Discontinuous Galerkin Methods for the Vlasov–Stokes System Vlasov-Stokes 系统的非连续伽勒金方法
IF 1.3 4区 数学 Q3 MATHEMATICS, APPLIED Pub Date : 2024-01-30 DOI: 10.1515/cmam-2023-0243
Harsha Hutridurga, Krishan Kumar, Amiya K. Pani
This paper develops and analyses a semi-discrete numerical method for the two-dimensional Vlasov–Stokes system with periodic boundary condition. The method is based on the coupling of the semi-discrete discontinuous Galerkin method for the Vlasov equation with discontinuous Galerkin scheme for the stationary incompressible Stokes equation. The proposed method is both mass and momentum conservative. Since it is difficult to establish non-negativity of the discrete local density, the generalized discrete Stokes operator become non-coercive and indefinite, and under the smallness condition on the discretization parameter, optimal error estimates are established with help of a modified the Stokes projection to deal with the Stokes part and, with the help of a special projection, to tackle the Vlasov part. Finally, numerical experiments based on the dG method combined with a splitting algorithm are performed.
本文针对具有周期性边界条件的二维 Vlasov-Stokes 系统,开发并分析了一种半离散数值方法。该方法基于 Vlasov 方程的半离散非连续 Galerkin 方法与静态不可压缩斯托克斯方程的非连续 Galerkin 方案的耦合。所提出的方法在质量和动量上都是保守的。由于离散局部密度的非负性难以确定,广义离散斯托克斯算子变得非强制和不确定,在离散化参数较小的条件下,借助修正的斯托克斯投影来处理斯托克斯部分,并借助特殊投影来处理 Vlasov 部分,从而建立了最佳误差估计。最后,进行了基于 dG 方法与分割算法相结合的数值实验。
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引用次数: 0
Robust Multigrid Methods for Discontinuous Galerkin Discretizations of an Elliptic Optimal Control Problem 用于椭圆最优控制问题非连续伽勒金离散化的鲁棒多网格方法
IF 1.3 4区 数学 Q3 MATHEMATICS, APPLIED Pub Date : 2024-01-30 DOI: 10.1515/cmam-2023-0132
Sijing Liu
We consider discontinuous Galerkin methods for an elliptic distributed optimal control problem, and we propose multigrid methods to solve the discretized system. We prove that the 𝑊-cycle algorithm is uniformly convergent in the energy norm and is robust with respect to a regularization parameter on convex domains. Numerical results are shown for both 𝑊-cycle and 𝑉-cycle algorithms.
我们考虑了椭圆分布式最优控制问题的非连续 Galerkin 方法,并提出了求解离散系统的多网格方法。我们证明了仸循环算法在能量规范上是均匀收敛的,并且在凸域上与正则化参数有关是稳健的。我们展示了 徼循环和 𝑉 循环算法的数值结果。
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引用次数: 0
Machine Learning Estimators: Implementation and Comparison in Python 机器学习估算器:Python 中的实现与比较
IF 1.3 4区 数学 Q3 MATHEMATICS, APPLIED Pub Date : 2024-01-24 DOI: 10.1515/cmam-2023-0198
Fabian Merle
We compare different machine learning estimators and present details about their implementation in Python. The computational studies are conducted for classification as well as regression problems. Moreover, as one of the founding problems of machine learning, we present the specific classification task of handwritten digit recognition. In this connection, we discuss the mathematical formulation and of course the implementation details of this problem. All corresponding Python code is fully provided on request and can be downloaded from the author’s GitHub page https://github.com/Fab1Fatal.
我们比较了不同的机器学习估计器,并详细介绍了它们在 Python 中的实现。我们针对分类和回归问题进行了计算研究。此外,作为机器学习的基础问题之一,我们介绍了手写数字识别的具体分类任务。在这方面,我们讨论了这个问题的数学表述,当然还有实现细节。所有相应的 Python 代码都会应要求提供,并可从作者的 GitHub 页面 https://github.com/Fab1Fatal 下载。
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引用次数: 0
Efficient P1-FEM for Any Space Dimension in Matlab Matlab 中任意空间维度的高效 P1-FEM
IF 1.3 4区 数学 Q3 MATHEMATICS, APPLIED Pub Date : 2024-01-24 DOI: 10.1515/cmam-2022-0239
Stefanie Beuter, Stefan A. Funken
This paper deals with the efficient implementation of the finite element method with continuous piecewise linear functions (P1-FEM) in R d mathbb{R}^{d} ( d N dinmathbb{N} ). Although at present there does not seem to be a very high practical demand for finite element methods that use higher-dimensional simplicial partitions, there are some advantages in studying the efficient implementation of the method independent of the dimension. For instance, it provides additional insights into necessary data structures and the complexity of implementations. Throughout, the focus is on an efficient realization using Matlab built-in functions and vectorization. The fast and vectorized Matlab function can be easily implemented in many other vector languages and is provided in Julia, too. The complete implementation of the adaptive FEM is given, including assembling stiffness matrix, building load vector, error estimation, and adaptive mesh-refinement. Numerical experiments underline the efficiency of our freely available code which is observed to be of a slightly more than linear complexity with respect to the number of elements when memory limits are not exceeded.
本文论述了在 R d mathbb{R}^{d} (d ∈ N dinmathbb{N} )中高效实现连续片断线性函数有限元方法(P1-FEM)。虽然目前对使用高维简单分区的有限元方法的实际需求似乎并不高,但研究独立于维数的方法的有效实现还是有一些优势的。例如,它为必要的数据结构和实现的复杂性提供了额外的见解。在整个过程中,重点是使用 Matlab 内置函数和矢量化来高效实现。快速的矢量化 Matlab 函数可以很容易地在许多其他矢量语言中实现,Julia 中也有提供。本文给出了自适应有限元的完整实现方法,包括装配刚度矩阵、构建载荷向量、误差估计和自适应网格细化。数值实验强调了我们免费提供的代码的效率,据观察,在不超过内存限制的情况下,该代码的复杂度略高于元素数量的线性关系。
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引用次数: 0
Simultaneous Reconstruction of Speed of Sound and Nonlinearity Parameter in a Paraxial Model of Vibro-Acoustography in Frequency Domain 频域振动声学准轴模型中声速和非线性参数的同步重构
IF 1.3 4区 数学 Q3 MATHEMATICS, APPLIED Pub Date : 2024-01-24 DOI: 10.1515/cmam-2023-0076
Barbara Kaltenbacher, Teresa Rauscher
In this paper, we consider the inverse problem of vibro-acoustography, a technique for enhancing ultrasound imaging by making use of nonlinear effects. It amounts to determining two spatially variable coefficients in a system of PDEs describing propagation of two directed sound beams and the wave resulting from their nonlinear interaction. To justify the use of Newton’s method for solving this inverse problem, on one hand, we verify well-definedness and differentiability of the forward operator corresponding to two versions of the PDE model; on the other hand, we consider an all-at-once formulation of the inverse problem and prove convergence of Newton’s method for its solution.
在本文中,我们考虑了振动声学的逆问题,这是一种利用非线性效应增强超声成像的技术。它相当于确定描述两束定向声波传播的 PDE 系统中的两个空间可变系数,以及它们非线性相互作用产生的波。为了证明使用牛顿法求解该逆问题的合理性,一方面,我们验证了与两个版本的 PDE 模型相对应的前向算子的定义明确性和可微分性;另一方面,我们考虑了逆问题的一次表述,并证明了牛顿法对其求解的收敛性。
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引用次数: 0
Robust PRESB Preconditioning of a 3-Dimensional Space-Time Finite Element Method for Parabolic Problems 抛物线问题三维时空有限元方法的稳健 PRESB 预处理
IF 1.3 4区 数学 Q3 MATHEMATICS, APPLIED Pub Date : 2024-01-24 DOI: 10.1515/cmam-2023-0085
Ladislav Foltyn, Dalibor Lukáš, Marco Zank
We present a recently developed preconditioning of square block matrices (PRESB) to be used within a parallel method to solve linear systems of equations arising from tensor-product discretizations of initial boundary-value problems for parabolic partial differential equations. We consider weak formulations in Bochner–Sobolev spaces and tensor-product finite element approximations for the heat and eddy current equations. The fast diagonalization method is employed to decouple the arising linear system of equations into auxiliary spatial complex-valued linear systems that can be solved concurrently. We prove that the real part of the system matrix is positive definite, which allows us to accelerate the flexible generalized minimal residual method (FGMRES) by the PRESB preconditioner. The action of PRESB on a vector includes two solutions with positive definite matrices. The spectrum of the preconditioned system lies between 1/2 and 1. Finally, we combine the PRESB-FGMRES method with multigrid-CG iterations and illustrate the numerical efficiency and the robustness for spatial discretizations up to 12 millions degrees of freedom.
我们介绍了最近开发的方块矩阵预处理方法(PRESB),该方法可用于并行方法,以解决抛物线偏微分方程初始边界值问题的张量乘积离散化所产生的线性方程组。我们考虑了 Bochner-Sobolev 空间中的弱公式以及热方程和涡流方程的张量积有限元近似。我们采用快速对角化方法,将产生的线性方程组解耦为可同时求解的辅助空间复值线性方程组。我们证明了系统矩阵的实部是正定的,这使我们能够通过 PRESB 预处理加速灵活的广义最小残差法(FGMRES)。PRESB 对矢量的作用包括两个具有正定矩阵的解。最后,我们将 PRESB-FGMRES 方法与多网格-CG 迭代相结合,说明了空间离散高达 1200 万自由度时的数值效率和鲁棒性。
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引用次数: 0
Quasi-Optimality of an AFEM for General Second Order Elliptic PDE 一般二阶椭圆 PDE 的 AFEM 的准光学性
IF 1.3 4区 数学 Q3 MATHEMATICS, APPLIED Pub Date : 2024-01-05 DOI: 10.1515/cmam-2023-0238
Arnab Pal, Thirupathi Gudi
In this article, convergence and quasi-optimal rate of convergence of an adaptive finite element method (in short, AFEM) is shown for a general second-order non-selfadjoint elliptic PDE with convection term b [ L ( Ω ) ] d {bin[L^{infty}(Omega)]^{d}} and using minimal regularity of the dual problem, i.e., the solution of the dual problem has only H 1 {H^{1}} -regularity, which extends the result [J. M. Cascon, C. Kreuzer, R. H. Nochetto and K. G. Siebert, Quasi-optimal convergence rate for an adaptive finite element method, SIAM J. Numer. Anal. 46 2008, 5, 2524–2550]. The theoretical results are illustrated by numerical experiments.
本文针对对流项 b∈ [ L ∞ ( Ω ) ] d {bin[L^{infty}(Omega)]^{d}} 的一般二阶非自洽椭圆 PDE,并利用对偶问题的最小正则性(即、对偶问题的解只有 H 1 {H^{1}} -正则性,从而扩展了结果[J.M. Cascon, C. Kreuzer, R. H. Nochetto and K. G. Siebert, Quasi-optimal convergence rate for an adaptive finite element method, SIAM J. Numer.Anal.46 2008, 5, 2524-2550].数值实验说明了理论结果。
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引用次数: 0
Numerical Approximation of Gaussian Random Fields on Closed Surfaces 封闭曲面上高斯随机场的数值逼近
IF 1.3 4区 数学 Q3 MATHEMATICS, APPLIED Pub Date : 2024-01-04 DOI: 10.1515/cmam-2022-0237
Andrea Bonito, Diane Guignard, Wenyu Lei
We consider the numerical approximation of Gaussian random fields on closed surfaces defined as the solution to a fractional stochastic partial differential equation (SPDE) with additive white noise. The SPDE involves two parameters controlling the smoothness and the correlation length of the Gaussian random field. The proposed numerical method relies on the Balakrishnan integral representation of the solution and does not require the approximation of eigenpairs. Rather, it consists of a sinc quadrature coupled with a standard surface finite element method. We provide a complete error analysis of the method and illustrate its performances in several numerical experiments.
我们考虑了封闭表面上高斯随机场的数值近似,其定义为带有加性白噪声的分数随机偏微分方程(SPDE)的解。SPDE 涉及两个参数,分别控制高斯随机场的平滑度和相关长度。所提出的数值方法依赖于解的 Balakrishnan 积分表示法,不需要对特征对进行近似。相反,它由 sinc 正交法和标准曲面有限元法组成。我们对该方法进行了完整的误差分析,并在几个数值实验中对其性能进行了说明。
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引用次数: 0
An Optimal Method for High-Order Mixed Derivatives of Bivariate Functions 双变量函数高阶混合导数的最优方法
IF 1.3 4区 数学 Q3 MATHEMATICS, APPLIED Pub Date : 2024-01-01 DOI: 10.1515/cmam-2023-0137
Evgeniya V. Semenova, Sergiy G. Solodky
The problem of optimal recovering high-order mixed derivatives of bivariate functions with finite smoothness is studied. Based on the truncation method, an algorithm for numerical differentiation is constructed, which is order-optimal both in the sense of accuracy and in terms of the amount of involved Galerkin information. Numerical examples are provided to illustrate the fact that our approach can be implemented successfully.
研究了有限平稳性双变量函数高阶混合导数的优化恢复问题。基于截断法,构建了一种数值微分算法,该算法在精度和所涉及的 Galerkin 信息量方面都是阶次最优的。我们提供了数值示例来说明我们的方法可以成功实施。
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引用次数: 0
Wave Propagation in High-Contrast Media: Periodic and Beyond 高对比度介质中的波传播:周期及其他
IF 1.3 4区 数学 Q3 MATHEMATICS, APPLIED Pub Date : 2024-01-01 DOI: 10.1515/cmam-2023-0066
Élise Fressart, Barbara Verfürth
This work is concerned with the classical wave equation with a high-contrast coefficient in the spatial derivative operator. We first treat the periodic case, where we derive a new limit in the one-dimensional case. The behavior is illustrated numerically and contrasted to the higher-dimensional case. For general unstructured high-contrast coefficients, we present the Localized Orthogonal Decomposition and show a priori error estimates in suitably weighted norms. Numerical experiments illustrate the convergence rates in various settings.
这项研究涉及空间导数算子中具有高对比度系数的经典波方程。我们首先处理周期性情况,在一维情况下推导出一个新的极限。我们用数值说明了这一行为,并与高维情况进行了对比。对于一般的非结构化高对比度系数,我们提出了局部正交分解,并以适当的加权规范显示了先验误差估计。数值实验说明了各种情况下的收敛速度。
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引用次数: 0
期刊
Computational Methods in Applied Mathematics
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