positive real functions
A multiplication-division theorem is derived for the positive real functions of two complex variables. The theorem is generalized to encompass the product of positive real functions of two complex variables. The theorem is generalized to encompass the product of positive real matrices whose elements are functions of two complex variables. PRF and PR matrices occur frequantly in the study of electrical multiports and multivariable systems (such as digital filters).
 N. K. Bose: Applied Multidimensional Systems Theory
. Van Nostrand Reinhold C., New York, 1982. MR 0652483
| Zbl 0574.93031
 W. Rudin: Function Theory in the Unit Ball of $C^n$
. Springer, Berlin, 1980. MR 0601594
 S. G. Krantz: Function Theory of Several Complex Variables
. John Wiley and Sons, New York, 1982. MR 0635928
| Zbl 0471.32008
 A. Fettweis G. Linnenberg: A Class of Two- Dimensional Reactance Functions With Applications. Archiv. Für Elektronik und Übertragungstechnik, vol. 34 (1980), pp. 276-278.
 T. Kоgа: Synthesis of Finite Passive n-Ports with Prescribed Two-variable Reactance Matrices. JEEE vol. CT- 13 (1966), pp. 31 - 52.
 F. M. Reza: Product of Inductive and Capacitive Operators. IEE Proc. vol. 129, Pt. G. No. 5, October 1982, pp. 241-244.