Convergence of Lagrange finite elements for the Maxwell eigenvalue problem in two dimensions

We consider finite element approximations of the Maxwell eigenvalue problem in two dimensions. We prove, in certain settings, convergence of the discrete eigenvalues using Lagrange finite elements. In particular, we prove convergence in three scenarios: piecewise linear elements on Powell-Sabin triangulations, piecewise quadratic elements on Clough-Tocher triangulations and piecewise quartics (and higher) elements on general shape-regular triangulations. We provide numerical experiments that support the theoretical results. The computations also show that, on general triangulations, the eigenvalue approximations are very sensitive to nearly singular vertices, i.e., vertices that fall on exactly two 'almost' straight lines.

Automated summary

This article examines finite element approximations of the two-dimensional Maxwell eigenvalue problem, proves the convergence of discrete eigenvalues using Lagrange finite elements in certain cases, and provides numerical experiments to support the theoretical results. The computations also reveal that the eigenvalue approximations are highly sensitive to nearly singular vertices on general triangulations.