The Schur-Horn theorem for operators with finite spectrum

Marcin Bownik, John Jasper

Published 2013-02-19Version 1

We characterize the set of diagonals of the unitary orbit of a self-adjoint operator with a finite spectrum. Our result extends the Schur-Horn theorem from a finite dimensional setting to an infinite dimensional Hilbert space analogous to Kadison's theorem for orthogonal projections and the second author's result for operators with three point spectrum.