English

Markov $L_2$-inequality with the Laguerre weight

Classical Analysis and ODEs 2017-05-11 v1

Abstract

Let wα(t):=tαetw_\alpha(t) := t^{\alpha}\,e^{-t}, where α>1\alpha > -1, be the Laguerre weight function, and let wα\|\cdot\|_{w_\alpha} be the associated L2L_2-norm, fwα={0f(x)2wα(x)dx}1/2. \|f\|_{w_\alpha} = \left\{\int_{0}^{\infty} |f(x)|^2 w_\alpha(x)\,dx\right\}^{1/2}\,. By Pn\mathcal{P}_n we denote the set of algebraic polynomials of degree n\le n. We study the best constant cn(α)c_n(\alpha) in the Markov inequality in this norm pnwαcn(α)pnwα,pnPn, \|p_n'\|_{w_\alpha} \le c_n(\alpha) \|p_n\|_{w_\alpha}\,,\qquad p_n \in \mathcal{P}_n\,, namely the constant cn(α):=suppnPnpnwαpnwα. c_n(\alpha) := \sup_{p_n \in \mathcal{P}_n} \frac{\|p_n'\|_{w_\alpha}}{\|p_n\|_{w_\alpha}}\,. We derive explicit lower and upper bounds for the Markov constant cn(α)c_n(\alpha), as well as for the asymptotic Markov constant c(α)=limncn(α)n. c(\alpha)=\lim_{n\rightarrow\infty}\frac{c_n(\alpha)}{n}\,.

Keywords

Cite

@article{arxiv.1705.03824,
  title  = {Markov $L_2$-inequality with the Laguerre weight},
  author = {Geno Nikolov and Alexei Shadrin},
  journal= {arXiv preprint arXiv:1705.03824},
  year   = {2017}
}

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12 pages