Compression and Reduced Representation Techniques for Patch-Based Relaxation

Patch-based relaxation refers to a family of methods for solving linear systems which partitions the matrix into smaller pieces often corresponding to groups of adjacent degrees of freedom residing within patches of the computational domain. The two most common families of patch-based methods are block-Jacobi and Schwarz methods, where the former typically corresponds to non-overlapping domains and the later implies some overlap. We focus on cases where each patch consists of the degrees of freedom within a finite element method mesh cell. Patch methods often capture complex local physics much more effectively than simpler point-smoothers such as Jacobi; however, forming, inverting, and applying each patch can be prohibitively expensive in terms of both storage and computation time. To this end, we propose several approaches for performing analysis on these patches and constructing a reduced representation. The compression techniques rely on either matrix norm comparisons or unsupervised learning via a clustering approach. We illustrate how it is frequently possible to retain/factor less than 5% of all patches and still develop a method that converges with the same number of iterations or slightly more than when all patches are stored/factored.Comment: 16 pages, 5 figure

Numerical Simulation of Multiphase Flow in Fractured Porous Media

Fractures provide preferred paths for flow and transport in many porous media. They have a significant influence on process behavior in groundwater remediation, reservoir engineering and safety analysis for waste repositories. We present a finite volume method for the numerical solution of the multiphase flow equations in fractured porous media. The capillary pressure is treated by an extended capillary pressure interface condition. The method is fully coupled and fully implicit and employs a mixed-dimensional formulation with lower dimensional elements in the fractures. The method features unstructured grids, adaptive refinement and multigrid methods. It is implemented for twodimensional and threedimensional complex problems with several million unknowns. Additionally, a discontinuous Galerkin method for the groundwater flow equation and its multigrid treatment is presented

Generalized averaged Gaussian quadrature and applications

A simple numerical method for constructing the optimal generalized averaged Gaussian quadrature formulas will be presented. These formulas exist in many cases in which real positive GaussKronrod formulas do not exist, and can be used as an adequate alternative in order to estimate the error of a Gaussian rule. We also investigate the conditions under which the optimal averaged Gaussian quadrature formulas and their truncated variants are internal

MS FT-2-2 7 Orthogonal polynomials and quadrature: Theory, computation, and applications

Quadrature rules find many applications in science and engineering. Their analysis is a classical area of applied mathematics and continues to attract considerable attention. This seminar brings together speakers with expertise in a large variety of quadrature rules. It is the aim of the seminar to provide an overview of recent developments in the analysis of quadrature rules. The computation of error estimates and novel applications also are described