English

Universal Taylor series on specific compact sets

Complex Variables 2015-06-05 v1

Abstract

Let DD be the open unit disc in the complex plane. We denote by C\mathbb{C} the set of complex numbers and consider any compact set KK which is disjoint from DD and which also has connected complement. Let A(K)A(K) denote all the functions f:KCf:K\to \mathbb{C} such that ff is continuous on KK and holomorphic in KoK^o. It is well known that there exist holomorphic functions ff on DD for which the partial sums Sn(f)S_n(f), n=1,2,... of the Taylor series with center 00 are dense in A(K)A(K) for every KK satisfying the properties above. It is also known that the above result fails if we consider the weighted polynomials 2nSn(f)2^nS_n(f), n=1,2,... instead of Sn(f)S_n(f), n=1,2,.... In the opposite direction, the main result of this work shows that there exist holomorphic functions ff on DD for which the sequence 2nSn(f)2^nS_n(f), n=1,2,...n=1,2,... is dense in A(K)A(K) for specific compact sets KK. In this case the geometry of KK plays a crucial role. We also generalize these results on arbitrary simply connected domains.

Keywords

Cite

@article{arxiv.1506.01528,
  title  = {Universal Taylor series on specific compact sets},
  author = {Nikos Tsirivas},
  journal= {arXiv preprint arXiv:1506.01528},
  year   = {2015}
}
R2 v1 2026-06-22T09:47:12.096Z