Geodesic
On the Constant and Step in Jackson's Inequality for Best Approximations by Trigonometric Polynomials and by Haar Polynomials
Matematičeskie zametki, Tome 100 (2016) no. 3, pp. 323-330.

Voir la notice de l'article provenant de la source Math-Net.Ru

Two sharp results for best approximations of periodic functions are established in this paper. We prove the sharpness of the step of the modulus of continuity in Jackson's inequality with least possible constant for approximations by trigonometric polynomials. We also prove the sharpness of the constants in a Jackson-type inequality for approximations by Haar polynomials in several variables.
Mots-clés : sharp constant
Keywords: Jackson's inequality, Haar system. 
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P. A. Andrianov; O. L. Vinogradov. On the Constant and Step in Jackson's Inequality for Best Approximations by Trigonometric Polynomials and by Haar Polynomials. Matematičeskie zametki, Tome 100 (2016) no. 3, pp. 323-330. http://geodesic.mathdoc.fr/item/MZM_2016_100_3_a0/

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