Approximation by nörlund means of hexagonal fourier series

Abstract

Let f be an H−periodic H ¨older continuous function of two real variables. The error k f −Nn (p; f)k is estimated in the uniform norm and in the H ¨older norm, where p=(pk)∞k=0 is a nonincreasing sequence of positive numbers and Nn (p; f) is the nth N ¨orlund mean of hexagonal Fourier series of f with respect to p=(pk) ∞k=0.