Tips for implementing multigrid methods on domains containing holes

Abstract

As part of our development of a computer code to perform 3D `constrained evolution' of Einstein's equations in 3+1 form, we discuss issues regarding the efficient solution of elliptic equations on domains containing holes (i.e., excised regions), via the multigrid method. We consider as a test case the Poisson equation with a nonlinear term added, as a means of illustrating the principles involved, and move to a "real world" 3-dimensional problem which is the solution of the conformally flat Hamiltonian constraint with Dirichlet and Robin boundary conditions. Using our vertex-centered multigrid code, we demonstrate globally second-order-accurate solutions of elliptic equations over domains containing holes, in two and three spatial dimensions. Keys to the success of this method are the choice of the restriction operator near the holes and definition of the location of the inner boundary. In some cases (e.g. two holes in two dimensions), more and more smoothing may be required as the mesh spacing decreases to zero; however for the resolutions currently of interest to many numerical relativists, it is feasible to maintain second order convergence by concentrating smoothing (spatially) where it is needed most. This paper, and our publicly available source code, are intended to serve as semi-pedagogical guides for those who may wish to implement similar schemes.

18 pages, 11 figures, LaTeX. Added clarifications and references re. scope of paper, mathematical foundations, relevance of work. Accepted for publication in Classical & Quantum Gravity

References in corpus (9)

• A simple construction of initial data for multiple black holes
• A multidomain spectral method for solving elliptic equations
• Einstein Constraints on Asymptotically Euclidean Manifolds
• An Axisymmetric Gravitational Collapse Code
• Physics and Initial Data for Multiple Black Hole Spacetimes
• Initial data for a head on collision of two Kerr-like black holes with close limit
• Spectral Methods for Numerical Relativity. The Initial Data Problem
• Diagonalizability of Constraint Propagation Matrices
• On the Effect of Constraint Enforcement on the Quality of Numerical Solutions in General Relativity

Cited by in corpus (6)

• A single-domain spectral method for black hole puncture data
• A double-domain spectral method for black hole excision data
• Numerical evolution of multiple black holes with accurate initial data
• Binary Black Hole merger in f(R) theory
• Initial Conditions for Numerical Relativity -- Introduction to numerical methods for solving elliptic PDEs
• High order convergent multigrid methods on domains containing holes for black hole initial data