On a theorem of Feingold
James Hardy Wilkinson · Linear Algebra and its Applications · 1987
We discuss an extension of a theorem which is apparently due to Feingold. Both the theorem and its extension follow mutatis mutandis from the corresponding material associated with the Bauer-Fike theorem. Feingold made no claims for his result and indeed referred to it as trivial. Although it proves to be rather disappointing, an understanding of the source of its weakness is instructive and leads to related techniques which are of greater value.