The Krein-von Neumann Extension of a Regular Even Order Quasi-Differential Operator

Abstract

We characterize by boundary conditions the Krein-von Neumann extension of a strictly positive minimal operator corresponding to a regular even order quasi-differential expression of Shin-Zettl type. The characterization is stated in terms of a specially chosen basis for the kernel of the maximal operator and employs a description of the Friedrichs extension due to M\"oller and Zettl.