Properties of moduli of smoothness in $L_p({\mathbb{R}}^d)$

Abstract

In this paper, we discuss various basic properties of moduli of smoothness of functions from $L_p({\mathbb{R}}^d)$, $0<p\le \infty$. In particular, complete versions of Jackson-, Marchaud-, and Ulyanov-type inequalities are given for the whole range of $p$. Moreover, equivalences between moduli of smoothness and the corresponding $K$-functionals and the realization concept are proved.