Nearest normal approximation for certain operators

John Phillips
1977 Proceedings of the American Mathematical Society  
In this paper we show that binormal operators have nearest normal approximants. In fact, we exhibit nearest normals to such operators and, as a corollary, show that the hermitian part of a binormal operator with real spectrum is a nearest normal. We obtain further corollaries on nearest normal approximation to operators which are square roots of normal operators and then apply these results to perturbations of operator algebras.
doi:10.1090/s0002-9939-1977-0458212-4 fatcat:xk2rsce5lnavvm767yzzqu45ju