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Remark on the degree of approximation of continuous functions by singular integrals. (English) Zbl 0808.42004

Let \(f\) be a bounded, real-valued function defined on the real line \(\mathbb{R}\) or \([-\pi,\pi]\). R. N. Mohapatra and R. S. Rodriguez [Math. Nachr. 149, 117-124 (1990; Zbl 0726.42003)] obtained the rate of convergence of singular integrals of \(f\) to \(f\) in the Hölder metric under the assumption: \[ t^{-1} \omega(f;t)\quad\text{is decreasing with }t>0,{(*)} \] where \(\omega(f;t)\) is the modulus of continuity of \(f\).
In the present paper, the author has shown that for \(f\in C_{2\pi}\), the estimates obtained by Mohapatra and Rodriguez (ibid.) may be obtained without using \((*)\).
Remark: The author has mentioned that Mohapatra and Rodriguez (ibid.) has obtained the rate of convergence for \(f\in C_{2\pi}\), which is not correct. In fact, these authors did not use the periodicity of \(f\).
Reviewer: P.Chandra (Ujjain)

MSC:

42A10 Trigonometric approximation
42A50 Conjugate functions, conjugate series, singular integrals
41A25 Rate of convergence, degree of approximation
41A35 Approximation by operators (in particular, by integral operators)

Citations:

Zbl 0726.42003
Full Text: DOI

References:

[1] Approximation of functions, Holt, Rinehart and Winston, New York, 1986
[2] Mohapatra, Math. Nachr. 149 pp 117– (1990) · Zbl 0726.42003 · doi:10.1002/mana.19901490108
[3] Peetre, Ricerche Mat. 18 pp 239– (1969)
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