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The direct and converse inequalities for Jackson-type operators on spherical cap. (English) Zbl 1187.41009

Summary: Approximation on the spherical cap is different from that on the sphere which requires us to construct new operators. This paper discusses the approximation on the spherical cap. That is, the so-called Jackson-type operator \(\{J_{k,s}^m\}_{k=1}^\infty\) is constructed to approximate the function defined on the spherical cap \(D(x_0,\gamma)\). We thus establish the direct and inverse inequalities and obtain saturation theorems for \(\{J_{k,s}^m\}_{k=1}^\infty\) on the cap \(D(x_0,\gamma)\). Using methods of \(K\)-functional and multiplier, we obtain the inequality \(C_1\|J_{k,s}^m(f)- f\|_{D,p}\leq \omega^2(f,k^{-1})_{D,p}\leq C_2 \max_{v\geq k}\|J_{v,s}^m(f)- f\|_{D,p}\) and that the saturation order of these operators is \(O(k^{-2})\), where \(\omega^2(f,t)_{D,p}\) is the modulus of smoothness of degree 2, the constants \(C_1\) and \(C_2\) are independent of \(k\) and \(f\).

MSC:

41A35 Approximation by operators (in particular, by integral operators)

References:

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