  Loewner matrix pencils play a central role in the system realization theory
of Mayo and Antoulas, an important development in data-driven modeling. The
eigenvalues of these pencils reveal system poles. How robust are the poles
recovered via Loewner realization? With several simple examples, we show how
pseudospectra of Loewner pencils can be used to investigate the influence of
interpolation point location and partitioning on pole stability, the transient
behavior of the realized system, and the effect of noisy measurement data. We
include an algorithm to efficiently compute such pseudospectra by exploiting
Loewner structure.
