Approximation by nonlinear q-Bernstein-Chlodowsky operators

Max-Product algebra is new direction in constructive approximation of functions by operators. In this study, we introduce the q-analog of Bernstein-Chlodowsky operators using max-product algebra and investigate approximation properties of a sequence of these operators. Also, an upper estimate of the approximation error of the form Cω1(f; 1/√n + 1) with C > 0 obvious constant is obtained.Publisher's Versio

On Sequences of J. P. King-Type Operators

This survey is devoted to a series of investigations developed in the last fifteen years, starting from the introduction of a sequence of positive linear operators which modify the classical Bernstein operators in order to reproduce constant functions and x2 on [0,1]. Nowadays, these operators are known as King operators, in honor of J. P. King who defined them, and they have been a source of inspiration for many scholars. In this paper we try to take stock of the situation and highlight the state of the art, hoping that this will be a useful tool for all people who intend to extend King's approach to some new contents within Approximation Theory. In particular, we recall the main results concerning certain King-type modifications of two well known sequences of positive linear operators, the Bernstein operators and the Szász-Mirakyan operators

Subspaces with equal closure

We take a unifying and new approach toward polynomial and trigonometric approximation in an arbitrary number of variables, resulting in a precise and general ready-to-use tool that anyone can easily apply in new situations of interest. The key idea is to show, in considerable generality, that a module, which is generated over the polynomials or trigonometric functions by some set, necessarily has the same closure as the module which is generated by this same set, but now over the compactly supported smooth functions. The particular properties of the ambient space or generating set are to a large degree irrelevant. This translation -- which goes in fact beyond modules -- allows us, by what is now essentially a straightforward check of a few properties, to replace many classical results by more general and stronger statements of a hitherto unknown type. As a side result, we also obtain a new integral criterion for multidimensional measures to be determinate. At the technical level, we use quasi-analytic classes in several variables and we show that two well-known families of one-dimensional weights are essentially equal. The method can be formulated for Lie groups and this interpretation shows that many classical approximation theorems are "actually" theorems on the unitary dual of n-dimensional real space. Polynomials then correspond to the universal enveloping algebra.Comment: 61 pages, LaTeX 2e, no figures. Second and final version, with minor changes in presentation. Mathematically identical to the first version. Accepted by Constructive Approximatio