ELA, Volume 11, pp. 1-15, January 2004, abstract.

On the Krein-Langer Integral Representation of
Generalized Nevanlinna Functions

by

J. Rovnyak and L.A. Sakhnovich

The Krein-Langer integral representation of a matrix-valued 
generalized Nevanlinna function arises in problems of spectral 
theory and interpolation.  A version of this formula which is 
suitable for such problems, and a corresponding Stieltjes inversion 
formula, are derived.  Some classes of generalized Nevanlinna 
functions which are defined in terms of behavior at infinity are 
characterized in terms of their integral representations.