
Journal of Convex Analysis 26 (2019), No. 2, 573592 Copyright Heldermann Verlag 2019 Ky Fan's Dominance Theorem and Eaton Triple Charles L. Dolberry Math/Science Division, Andrew College, Cuthbert, GA 39840, U.S.A. charlesdolberry@andrewcollege.edu TinYau Tam Department of Mathematics and Statistics, University of Nevada, Reno, NV 89557, U.S.A. ttam@unr.edu A generalization of the Dominance Theorem of Ky Fan on the unitarily invariant norm is obtained in the content of Eaton triple. The results of Zietak on the characterization of the set of dual matrices of a given matrix and the faces of the unit ball, both with respect to a unitarily invariant norm, are also extended in the same context. The notion of dual matrices of a given matrix A with respect to a unitarily invariant norm is related to the subdifferential of the norm at A. A generalization of So's characterization of the extreme points of the unit ball is given. Keywords: Ky Fan's Dominance Theorem, Eaton triple, unitarily invariant norm, extreme point, unit ball. MSC: 90C31, 15A18 [ Fulltextpdf (167 KB)] for subscribers only. 