2002/09/18 by William Fulton
Mathematics · #math.RA #math.AC #math.AG
published as Lin. Alg. Appl. 319 (2000), 23--36 · 12 pages
arxiv created 2002/09/18 · arxiv updated 2009/11/30
Answering a question raised by S. Friedland, we show that the possible eigenvalues of Hermitian matrices (or compact operators) A, B, and C with C <= A + B are given by the same inequalities as in Klyachko's theorem for the case where C = A + B, except that the equality corresponding to tr(C) = tr(A) + tr(B) is replaced by the inequality corresponding to tr(C) <= tr(A) + tr(B). The possible types of finitely generated torsion modules A, B, and C over a discrete valuation ring such that there is an exact sequence B -> C -> A are characterized by the same inequalities.