Abstract:
We obtain asymptotic estimates for best approximations by trigonometric polynomials in the metric of the space $C(L_p)$ for classes of periodic functions expressible as convolutions of kernels $\Psi_\beta$ with Fourier coefficients decreasing to zero faster than any power sequence, and with functions $\varphi\in C$$(\varphi\in L_p)$ whose moduli of continuity do not exceed the given majorant of $\omega(t)$. It is proved that, in the spaces $C$ and $L_1$, for convex moduli of continuity $\omega(t)$, the obtained estimates are asymptotically sharp.
Keywords:best approximation by trigonometric polynomials, periodic infinitely differentiable function, modulus of continuity, generalized Poisson kernel, linear approximation method, Kolmogorov–Nikol'skii problem.