Edmundo José HUERTAS CEJUDO, Francisco MARCELLÁN ESPAÑOL, Maria Francisca PEREZ VALERO, Yamilet QUINTANA

A Cohen type inequality for Laguerre--Sobolev expansions with a mass point outside their oscillatory regime

Let consider the Sobolev type inner product \langle f, g\rangleS = \int0\infty f(x)g(x)d m (x) + Mf(c)g(c) + Nf\prime(c) g\prime(c), where dm (x) = xa e-xdx, a > -1, is the Laguerre measure, c < 0, and M, N \geq 0. In this paper we get a Cohen-type inequality for Fourier expansions in terms of the orthonormal polynomials associated with the above Sobolev inner product. Then, as an immediate consequence, we deduce the divergence of Fourier expansions and Cesàro means of order d in terms of this kind of Laguerre--Sobolev polynomials.

Anahtar Kelimeler:

Sobolev-type orthogonal polynomials, Cohen-type inequality, Fourier--Sobolev expansions

A Cohen type inequality for Laguerre--Sobolev expansions with a mass point outside their oscillatory regime

Keywords:

Sobolev-type orthogonal polynomials, Cohen-type inequality, Fourier--Sobolev expansions,

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