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arXiv · 1410.0134

A Note on the Maximum Number of Zeros of $r(z) - \bar{z}$

Robert Luce·Olivier Sète·Jörg Liesen
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Abstract

An important theorem of Khavinson & Neumann (Proc. Amer. Math. Soc. 134(4), 2006) states that the complex harmonic function $r(z) - \bar{z}$, where $r$ is a rational function of degree $n \geq 2$, has at most $5 (n - 1)$ zeros. In this note we resolve a slight inaccuracy in their proof and in addition we show that for certain functions of the form $r(z) - \bar{z}$ no more than $5 (n - 1) - 1$ zeros can occur. Moreover, we show that $r(z) - \bar{z}$ is regular, if it has the maximal number of zeros.

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Robert Luce, Olivier Sète, Jörg Liesen. 2014-10-01. A Note on the Maximum Number of Zeros of $r(z) - \bar{z}$. https://doi.org/10.1007/s40315-015-0110-6

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