English

Universal Pad\'{e} approximants and their behaviour on the boundary

Complex Variables 2013-10-08 v1

Abstract

There are several kinds of universal Taylor series. In one such kind the universal approximation is required at every boundary point of the domain of definition \OO\OO of the universal function ff. In another kind the universal approximation is not required at any point of \OO\partial\OO but in this case the universal function ff can be taken smooth on \oO\oO and, moreover, it can be approximated by it's Taylor partial sums on every compact subset of \oO\oO. Similar generic phenomena hold when the partial sums of the Taylor expansion of the universal function are replaced by some Pad\'{e} approximants of it. In the present paper we show that in the case of Pad\'{e} approximants, if \OO\OO is an open set and S,TS,T are two subsets of \OO\partial\OO that satisfy some conditions, then there exists a universal function fH(\OO)f\in H(\OO) which is smooth on \OOS\OO\cup S and has some Pad\'{e} approximants that approximate ff on each compact subset of \OOS\OO\cup S and simultaneously obtain universal approximation on each compact subset of (\C\sm\oO)T(\C\sm\oO)\cup T. A sufficient condition for the above to happen is \oS\oT=\oS\cap\oT=\emptyset, while a necessary and sufficient condition is not known.

Keywords

Cite

@article{arxiv.1310.1509,
  title  = {Universal Pad\'{e} approximants and their behaviour on the boundary},
  author = {Ilias Zadik},
  journal= {arXiv preprint arXiv:1310.1509},
  year   = {2013}
}

Comments

arXiv admin note: text overlap with arXiv:1212.4394

R2 v1 2026-06-22T01:41:01.049Z