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Approximating classes of functions defined by a generalised modulus of smoothness. (English) Zbl 1353.41005
Summary: In the present paper, we use a generalised shift operator in order to define a generalised modulus of smoothness. By its means, we define generalised Lipschitz classes of functions, and we give their constructive characteristics. Specifically, we prove certain direct and inverse types theorems in approximation theory for best approximation by algebraic polynomials.
##### MSC:
 41A35 Approximation by operators (in particular, by integral operators) 41A50 Best approximation, Chebyshev systems 42A16 Fourier coefficients, Fourier series of functions with special properties, special Fourier series
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