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On the stability of some classical operators from approximation theory. (English) Zbl 1284.39032

An operator \(T\) mapping a normed space \(A\) into a normed space \(B\) is Hyers-Ulam stable (HU-stable) iff there exists a constant \(K\) such that for any \(g\in T(A)\), \(\varepsilon>0\) and \(f\in A\) such that \(\|Tf-g\|\leq\varepsilon\), there exists \(f_0\in A\) such that \(Tf_0=g\) and \(\|f-f_0\|\leq K\varepsilon\). The infimum of all constants \(K\) is denoted by \(K_T\).
The paper deals with HU-stability of several classical operators from approximation theory. In particular, the stability of Bernstein operators \(B_n\) is proved and the constant \(K_{B_n}\) is determined. For the Szász-Mirakjan operators \(L_n\) the lack of stability is shown. The other considered operators are: the Meyer-König and Zeller operators, Kantorovich, Durmeyer, Bernstein-Durmeyer and beta integral operators, projections and others.

MSC:

39B82 Stability, separation, extension, and related topics for functional equations
41A35 Approximation by operators (in particular, by integral operators)
41A44 Best constants in approximation theory
39B52 Functional equations for functions with more general domains and/or ranges
Full Text: DOI

References:

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