FEM for Elliptic Eigenvalue Problems: How Coarse Can the Coarsest Mesh be Chosen? An Experimental Study

In this paper, we consider the numerical discretization of elliptic eigenvalue problems by Finite Element Methods and its solution by a multigrid method. From the general theory of finite element and multigrid methods, it is well known that the asymptotic convergence rates become visible only if the mesh width h is sufficiently small, h ≤ h0. We investigate the dependence of the maximal mesh width h0 on various problem parameters such as the size of the eigenvalue and its isolation distance. In a recent paper [19], the dependence of h0 on these and other parameters has been investigated theoretically. The main focus of this paper is to perform systematic experimental studies to validate the sharpness of the theoretical estimates and to get more insights in the convergence of the eigenfunctions and -values in the pre-asymptotic regime.