[1] W. R. Hamilton, Dublin Univ. Rev. Quarterly Mag. 1, 795 (1833).
[2] T. M. Jeong, D.-K. Ko, and J. Lee, Opt. Lett. 30, 3009 (2005).
[3] V. N. Mahajan, J. Opt. Soc. Am. A 17, 2223 (2000).
[4] L. N. Trefethen and M. Embree, Spectra and Pseudospectra: The Behavior of Nonnormal Matrices and Operators (Princeton University Press, Princeton, 2004).
[5] T. G. Wright, EigTool. http://www.comlab.ox.ac.uk/pseudospectra/eigtool/ (2002).