Some problems of trigonometric approximation on hexagonal domains

In this thesis consisting of five chapters, some approximation properties of T-transforms of hexagonal Fourier series with respect to matrix A have been investigated. In the first chapter, a general introduction is presented about the purpose, scope and method of the study. In the second chapter, the basic definitions and concepts that will be used throughout the thesis are given. In the third chapter, lattice structures and Fourier series defined with the help of these structures are discussed. In the fourth chapter, hexagonal lattices and hexagonal Fourier series are introduced. In the fifth chapter, the T-transformation of hexagonal Fourier series with respect to matrix A and the speed of approximation in the uniform norm are examined. KEYWORDS: Hexagonal Fourier series, hexagonal lattice, T− transformation with respect to an A-matrix, speed of approximation