English

Rational functions that share finite values with their first derivative

Complex Variables 2025-09-11 v1

Abstract

We treat shared value problems for rational functions R(z)R(z) and their derivative R(z)R'(z) in the plane and on the sphere. We also consider shared values for the pair R(w)R(w) and zR=λwR(w)\partial_{z} R = \lambda w \cdot R'(w) on C{0}{\mathbb C} \setminus \{ 0 \} and C^\widehat{\mathbb C}, again with rational functions RR. In C{0}{\mathbb C} \setminus \{ 0 \} this is related to shared values of meromorphic functions f:CC^f : {\mathbb C} \to \widehat{\mathbb C} and ff' through f(z)=R(w)f(z)=R(w) with w=exp(λz)w=\exp(\lambda z), while on C^\widehat{\mathbb C} this is connected to shared limit values in a similar fashion.

Keywords

Cite

@article{arxiv.2509.08517,
  title  = {Rational functions that share finite values with their first derivative},
  author = {Andreas Sauer and Andreas Schweizer},
  journal= {arXiv preprint arXiv:2509.08517},
  year   = {2025}
}

Comments

28 pages

R2 v1 2026-07-01T05:29:56.555Z