A note on the Hoffman-Wielandt theorem

Elsner L. A note on the Hoffman-Wielandt theorem. Linear algebra and its applications. 1993;182:235-237.An elementary proof of a recent generalization of the Hoffman-Wielandt theorem to commuting m-tuples of normal matrices by Bhatia and Bhattacharyya is given. In the case m = 1 this provides a derivation, which, though using the same tools, avoids some unnecessary calculations and is thus shorter than the original one and that to be found in the standard literature