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Extremal Rational Functions on Several Arcs of the Unit Circle with Zeros on these Arcs

The solution of anextrema lproblem aboutrational function with fixed denominator and leading coefficient of nominator which is deviatedleast from zero on several arcs of the unit circle is given under restrictions on the location of zeros and additional conditions on mutual position of the arcs and zeros of denominator. The extremal function is represented in terms of the density of harmonic measure.

Approximation of Functions of Bounded p-variation by Euler Means

In this paper we study the Euler means
eqn(f)(x) =∑k=0n(nk)qn−k(1 + q)−nSk(f)(x), q > 0, n ∈ Z+,

Several Questions of Approximation by Polynomials with Respect to Multiplicative Systems in Weighted Lp Spaces

In this paper we study approximation by Vilenkin polynomials in weighted Lp spaces. We prove the Butzer – Scherer type result on equivalence between the rate of best approximation of a function f and the growth of generalized derivatives and approximating properties of the best approximation polynomial tn(f). Some applications to the approximation by linear means of the Fourier – Vilenkin series are given.

Approximation of the Riemann–Liouville Integrals by Algebraic Polynomials on the Segment

The direct approximation theorem by algebraic polynomials is proved for Riemann–Liouville integrals of order r>0. As a corollary, we obtain asymptotic equalities for ε-entropy of the image of a Hölder type class under Riemann–Liouville integration operator.

Approximation of Bounded p-variation Periodic Functions by Generalized Abel–Poisson and Logarithmic Means

An asymptotic estimate of approximation by generalized Abel–Poisson means in p-variation metric on the class of functions with given majorant of p-variational best approximation is proved. Several other quantity results on approximation by these means are
obtained.