Pseudospectral functions of various dimensions for symmetric systems with the maximal deficiency index

Abstract

We consider first-order symmetric system Jy′ −A(t)y = λ∆(t)y with n×n-matrix coefficients defined on an interval [a, b) with the regular endpoint a. It is assumed that the deficiency indices N± of the system satisfies N− ≤ N+ = n. The main result is a parametrization of all pseudospectral functions σ(•) of any possible dimension nσ ≤ n by means of a Nevanlinna parameter τ = {C₀ (λ), C₁ (λ)}.