Degree of approximation by means of hexagonal Fourier series

Abstract

Let f be a continuous function which is periodic with respect to the hexagon lattice, and let A be a lowertriangular infinite matrix of nonnegative real numbers with nonincreasing rows. The degree of approximation of thefunction f by matrix means $T_{n^{(A)}};(f)$ of its hexagonal Fourier series is estimated in terms of the modulus of continuityof f.