English

Taylor Domination, Tur\'an lemma, and Poincar\'e-Perron Sequences

Classical Analysis and ODEs 2014-11-19 v2

Abstract

We consider "Taylor domination" property for an analytic function f(z)=k=0akzk,f(z)=\sum_{k=0}^{\infty}a_{k}z^{k}, in the complex disk DRD_R, which is an inequality of the form akRkC maxi=0,,N aiRi, kN+1. |a_{k}|R^{k}\leq C\ \max_{i=0,\dots,N}\ |a_{i}|R^{i}, \ k \geq N+1. This property is closely related to the classical notion of "valency" of ff in DRD_R. For ff - rational function we show that Taylor domination is essentially equivalent to a well-known and widely used Tur\'an's inequality on the sums of powers. Next we consider linear recurrence relations of the Poincar\'e type ak=j=1d[cj+ψj(k)]akj,  k=d,d+1,,with limkψj(k)=0. a_{k}=\sum_{j=1}^{d}[c_{j}+\psi_{j}(k)]a_{k-j},\ \ k=d,d+1,\dots,\quad\text{with }\lim_{k\rightarrow\infty}\psi_{j}(k)=0. We show that the generating functions of their solutions possess Taylor domination with explicitly specified parameters. As the main example we consider moment generating functions, i.e. the Stieltjes transforms Sg(z)=g(x)dx1zx. S_{g}\left(z\right)=\int\frac{g\left(x\right)dx}{1-zx}. We show Taylor domination property for such SgS_{g} when gg is a piecewise D-finite function, satisfying on each continuity segment a linear ODE with polynomial coefficients.

Keywords

Cite

@article{arxiv.1301.6033,
  title  = {Taylor Domination, Tur\'an lemma, and Poincar\'e-Perron Sequences},
  author = {Dmitry Batenkov and Yosef Yomdin},
  journal= {arXiv preprint arXiv:1301.6033},
  year   = {2014}
}