Neittaanmäki, Pekka, and Rainer Picard. “On the Convergence of the Finite Element Approximation of Eigenfrequencies and Eigenvectors to Maxwell’s Boundary Value Problem”. Annales Fennici Mathematici 6, no. 2 (August 1, 1981): 255–271. Accessed April 10, 2025. https://afm.journal.fi/article/view/134416.