Nevanlinna-Pick Interpolation On Certain Subalgebras of $H^{\infty}(\mathbb{D})$

Abstract

Given a collection $K$ of positive integers, let $H^{\infty}_K(\mathbb{D})$ denote the set of all bounded analytic functions defined on the unit disk $\mathbb{D}$ in $\mathbb{C}$ whose $k^{\text{th}}$ derivative vanishes at zero, for all $k \in K$. In this paper, we establish a Nevanlinna-Pick interpolation result for the subalgebra $H^{\infty}_K(\mathbb{D})$, where $K = \{1,2,\dotsc,k\}$, which is a slight generalization of the interpolation theorem that Davidson, Paulsen, Raghupathi, and Singh proved for the algebra $H^{\infty}_{\{1\}}(\mathbb{D})$. Furthermore, we provide a sufficient condition for an interpolation function to exist in the algebra $H^{\infty}_K(\mathbb{D})$ for a given $K$. Lastly, we give a necessary condition for the existence of such interpolation functions.