Wilhelm Wirtinger

Wilhelm Wirtinger was an Austrian mathematician born in 1865 at Ybbs an der Donau, who studied at the University of Vienna, where he received his doctorate in 1887 and his habilitation in 1890. He was greatly influenced by Felix Klein, with whom he studied at Berlin and Göttingen. He worked in complex analysis, geometry, algebra, number theory, Lie groups and knot theory, publishing 71 works, and his first significant paper, in 1896, was on theta functions. In an 1897 paper he proposed the spectrum of an operator as a generalization of eigenvalues, a concept later extended by David Hilbert and now central to spectral theory. In 1907 the Royal Society awarded him the Sylvester Medal.