Operator Algebras, Operator Theory and Applications
The nondegenerate Nevanlinna-Pick-Caratheodory-Fejer interpolation problem with finitely many interpolation conditions always has infinitely many solutions in a generalized Schur class S(kappa) for every kappa >= kappa(min) where the integer kappa(min) equals the number of negative eigenvalues of the Pick matrix associated to the problem and completely determined by interpolation data. A linear fractional description of all S(kappa min) solutions of the (nondegenerate) problem is well known. In this paper, we present a similar result for an arbitrary kappa >= kappa(min).
Bolotnikov, V. (2009). On an interpolation problem for generalized Schur functions. In Operator Algebras, Operator Theory and Applications (pp. 83-101). Birkhäuser Basel.