Variation of the one-dimensional centered maximal operator on simple functions with gaps between pieces

Abstract

Let $M$ denote the centered Hardy--Littlewood operator on $\mathbb{R}$. We prove that \[ {\rm Var} (Mf)\le {\rm Var} (f) - \frac12\big| |f(\infty)|-|f(-\infty)|\big| \] for piecewise constant functions $f$ with nonzero and zero values alternating. The above inequality strengthens a recent result of Bilz and Weigt \cite{BW} proved for indicator functions of bounded variation vanishing at $\pm \infty$. We conjecture that the inequality holds for all functions of bounded variation, representing a stronger version of the existing conjecture $\mathrm{Var}(Mf)\le \mathrm{Var}(f)$. We also obtain the discrete counterpart of our theorem, moreover proving a transference result on equivalency between both settings that is of independent interest.

10 pages