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 lower triangular infinite matrix of nonnegative real numbers with nonincreasing rows. The degree of approximation of the function f by matrix means T-n((A)) (f) of its hexagonal Fourier series is estimated in terms of the modulus of continuity of f.