Estimations of the best approximations of classes of infinitely differentiable functions in uniform and integral metrics

Abstract

We find uniform with respect to parameter $p \ (1\leq p\leq\infty)$ upper estimations of best approximations by trigonometric polynomials of classes $C^{\psi}_{\beta,p}$ of periodic functions generated by sequences $\psi(k)$, that decrease to nought faster than any power function. Obtained estimations are exact for order and have constants that are written in explicit form and depend on function $\psi$ only. We obtain analogical estimations for best approximations of classes $L^{\psi}_{\beta,1}$ in metrics of spaces $L_{s}$, $1\leq s\leq \infty$.