The Nevanlinna-Pick matrix interpolation in the Carath\'eodory class   with infinite data both in the nondegenerate and degenerate cases
  In this paper we study the Nevanlinna-Pick matrix interpolation problem in the Carath\'eodory class with infinite data (both in the nondegenerate and degenerate cases). We develop the Sz\"okefalvi-Nagy and Kor\'anyi operator approach to obtain an analytic description of all solutions of the problem. Simple necessary and sufficient conditions for the determinacy of the problem are given. 
Sergey M. Zagorodnyuk
math.FA