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Published in last 50 years
In this note we give a counterexample to a result of Z. Ditzian and K. Ivanov. A direct theorm, on C[0,1] is also presented for Kantorovich operators and Bernstein-Durrmeyer operators.
We prove a global inverse result for simultaneous approximation by modified Bernstein operators as introduced by Durrmeyer in 1967. The main result of this note supplements and extends an earlier direct theorem of Heilmann and Müller and is given in terms of the so-called Ditzian-Totik modulus of second order.
In this paper, we consider weighted approximation by Bernstein-Durrmeyer operators in Lp[0, 1] (1≤p≤∞), where the weight function w(x)=xα(1−x)β,−1/p<α, β<1-1/p. We obtain the direct and converse theorems. As an important tool we use appropriate K-functionals.
In this paper we introduce a new K-functional which is especially useful for non-Feller operators. Inverse theorems for multidimensional Bernstein-Sikkema and Bernstein-Durrmeyer operators are given on a simplex and on a cube.