Thompson, Robert T; Cummer, S A; Frauendiener, J; Thompson, Robert T; Department of Mathematics and Statistics, University of Otago, PO Box 56, Dunedin, 9054, New Zealand; Cummer, S A; Department of Electrical and Computer Engineering and Center for Metamaterials and Integrated Plasmonics, Duke University, Durham, NC 27708, USA; Frauendiener, J; Department of Mathematics and Statistics, University of Otago, PO Box 56, Dunedin, 9054, New Zealand ; Centre of Mathematics for Applications, University of Oslo, PO Box 1053, Blindern, NO-0316 Oslo, Norway