Quasi-Herglotz functions and convex optimization
Abstract
We introduce the set of quasi-Herglotz functions and demonstrate that it has properties useful in the modeling of non-passive systems. The linear space of quasi-Herglotz functions constitutes a natural extension of the convex cone of Herglotz functions. It consists of differences of Herglotz functions, and we show that several of the important properties and modeling perspectives are inherited by the new set of quasi-Herglotz functions. In particular, this applies to their integral representations, the associated integral identities or sum rules (with adequate additional assumptions), their boundary values on the real axis and the associated approximation theory. Numerical examples are included to demonstrate the modeling of a non-passive gain media formulated as a convex optimization problem, where the generating measure is modeled by using a finite expansion of B-splines and point masses.
Cite
@article{arxiv.1812.08319,
title = {Quasi-Herglotz functions and convex optimization},
author = {Yevhen Ivanenko and Mitja Nedic and Mats Gustafsson and B. L. G. Jonsson and Annemarie Luger and Sven Nordebo},
journal= {arXiv preprint arXiv:1812.08319},
year = {2021}
}
Comments
23 pages, 5 figures. Updated Introduction and Sections 2.1 and 2.4. Restructured and updated Section 5. New numerical example in Section 5.3