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Necessary Conditions to
Obtain A Voronovskaja Type Asymptotic Formula via Statistical Limit
Prof. Ogun Dogru
Gazi University
Faculty of Sciences and Arts,
Department of Mathematics
06500 Teknik Okullar
Ankara, Turkey
E. Mail: ogun.dogru@gazi.edu.tr
URL:
http://science.ankara.edu.tr/~dogru
Abstract: It is well-known that, obtaining the necessary
and sufficient conditions is not an easy task in the approximation theory.
Necessary and sufficient conditions for the uniform approximation of a
continuous function on a closed interval by positive linear operators are
independently obtained by H. Bohman and P.P. Korovkin. These theorems are
known as Bohman-Korovkin type, especially Korovkin type, theorems in the
literature. Obtaining the direct and inverse results for positive linear
operators is also important in this theory. The first inverse results for
the Bernstein polynomials were given by G.G. Lorentz. And then many authors
interested in these type researches. Some direct and inverse results for
Gadjiev, Ibragimov operators have been obtained by A. Alt?n and O. Dogru in
the previous WSEAS International conference on Applied Mathematics 2004. In
a recent paper, necessary and sufficient conditions to obtain direct and
inverse results for a sequence of general positive linear operators are
given by O. Dogru. These results are valid for not only uniform
approximation but also statistical approximation. The concept of statistical
convergence was defined by H. Fast. Recently, a useful Korovkin type theorem
for statistical convergence is proved by A.D. Gadjiev and C. Orhan. The
importance of statistical convergence is that any convergent sequence is
statistical convergent but not conversely. On the other hand, Voronovskaja
obtained an asymptotic formula for the rate of convergence of Bernstein
polynomials. Several studies showed that other many positive linear
operators such as Meyer-Konig and Zeller operators, Bleimann, Butzer and
Hahn operators, Lupas operators, Muller's Gamma operators, Kirov operators
and their Kantorovich and Durrmeyer type integral generalizations have some
asymptotic approximations. The main purpose of this talk is to give
necessary conditions to obtain a Voronovskaja type asymptotic formula for a
sequence of general positive linear operators via statistical limit. |