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Proceedings of the American Mathematical Society
Proceedings of the American Mathematical Society
ISSN 1088-6826(e) ISSN 0002-9939(p)

     

The $L_p$ version of Newman's Inequality for lacunary polynomials

Author(s): Peter Borwein; Tamás Erdélyi
Journal: Proc. Amer. Math. Soc. 124 (1996), 101-109.
MSC (1991): Primary 41A17; Secondary 30B10, 26D15
MathSciNet review: 1285974
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Abstract | References | Similar articles | Additional information

Abstract: The principal result of this paper is the establishment of the essentially sharp Markov-type inequality

\begin{equation*}\|xP^{\prime }(x)\|_{L_p[0,1]} \leq \left (1/p+12 \left({\sum ^n_{j=0}}(\lambda _j + 1/p)\right)\right) \|P\|_{L_p[0,1]} \end{equation*}

for every $P \in \text{span}\{x^{\lambda _0}, x^{\lambda _1}, \ldots , x^{\lambda _n}\}$ with distinct real exponents $\lambda _j$ greater than $-1/p$ and for every $p \in [1, \infty ]$. A remarkable corollary of the above is the Nikolskii-type inequality

\begin{equation*}\|y^{1/p}P(y)\|_{L_\infty [0,1]} \leq 13 \left({\sum ^n_{j=0}}(\lambda _j + 1/p)\right)^{1/p} \|P\|_{L_p[0,1]} \end{equation*}

for every $P \in \text{\rm span}\{x^{\lambda _0}, x^{\lambda _1}, \ldots , x^{\lambda _n}\}$ with distinct real exponents $\lambda _j$ greater than $-1/p$ and for every $p \in [1, \infty ]$. Some related results are also discussed.


References:

1.
P. B. Borwein and T. Erdélyi, Polynomials and polynomials inequalities, Springer-Verlag, New York (to appear).

2.
------, The full Müntz theorem in $C[0,1]$, $L_2[0,1]$, and $L_1[0,1]$, J. London Math. Soc. (to appear).

3.
------, Müntz systems and orthogonal Müntz--Legendre polynomials, Trans. Amer. Math. Soc. 342 (1994), 523--542. MR 94f:42026.

4.
C. Frappier, Quelques problemes extremaux pour les polynomes at les functions entieres de type exponentiel, Université de Montréal, Québec, 1982.

5.
D. J. Newman, Derivative bounds for Müntz polynomials, J. Approx. Theory 18 (1976), 360--362. MR 55:3609


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Additional Information:

Peter Borwein
Affiliation: Department of Mathematics, Simon Fraser University, Burnaby, British Columbia, Canada V5A 1S6

Tamás Erdélyi
Affiliation: Department of Mathematics, Simon Fraser University, Burnaby, British Columbia, Canada V5A 1S6

DOI: 10.1090/S0002-9939-96-03022-5
PII: S 0002-9939(96)03022-5
Keywords: Müntz polynomials, lacunary polynomials, Dirichlet sums, Markov-type inequality, $L_p$ norm
Received by editor(s): June 28, 1994
Additional Notes: The research of the first author was supported, in part, by NSERC of Canada. The research of the second author was supported, in part, by NSF under Grant No. DMS-9024901 and conducted while an NSERC International Fellow at Simon Fraser University.
Communicated by: J. Marshall Ash
Copyright of article: Copyright 1996, American Mathematical Society




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