English

Weighted holomorphic polynomial approximation

Complex Variables 2024-01-23 v1 Classical Analysis and ODEs

Abstract

For GG an open set in C\mathbb{C} and WW a non-vanishing holomorphic function in GG, in the late 1990's, Pritsker and Varga characterized pairs (G,W)(G,W) having the property that any ff holomorphic in GG can be locally uniformly approximated in GG by weighted holomorphic polynomials {W(z)npn(z)}, deg(pn)n\{W(z)^np_n(z)\}, \ deg(p_n)\leq n. We further develop their theory in first proving a quantitative Bernstein-Walsh type theorem for certain pairs (G,W)(G,W). Then we consider the special case where W(z)=1/(1+z)W(z)=1/(1+z) and GG is a loop of the lemniscate {zC:z(z+1)=1/4}\{z\in \mathbb{C}: |z(z+1)|=1/4\}. We show the normalized measures associated to the zeros of the nthn-th order Taylor polynomial about 00 of the function (1+z)n(1+z)^{-n} converge to the weighted equilibrium measure of G\overline G with weight W|W| as nn\to \infty. This mimics the motivational case of Pritsker and Varga where GG is the inside of the Szego curve and W(z)=ezW(z)=e^{-z}. Lastly, we initiate a study of weighted holomorphic polynomial approximation in Cn, n>1\mathbb{C}^n, \ n>1.

Keywords

Cite

@article{arxiv.2401.11955,
  title  = {Weighted holomorphic polynomial approximation},
  author = {S. Charpentier and N. Levenberg and F. Wielonsky},
  journal= {arXiv preprint arXiv:2401.11955},
  year   = {2024}
}

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21 pages