On Hardy type inequalities for weighted quasideviation means

Abstract

Using recent results concerning the homogenization and the Hardy property of weighted means, we establish sharp Hardy constants for concave and monotone weighted quasideviation means and for a few particular subclasses of this broad family. More precisely, for a mean $\mathscr{D}$ like above and a sequence $(\lambda_n)$ of positive weights such that $\lambda_n/(\lambda_1+\dots+\lambda_n)$ is nondecreasing, we determine the smallest number $H \in (1,+\infty]$ such that $$ \sum_{n=1}^\infty \lambda_n \mathscr{D}\big((x_1,\dots,x_n),(\lambda_1,\dots,\lambda_n)\big) \le H \cdot \sum_{n=1}^\infty \lambda_n x_n \text{ for all }x \in \ell_1(\lambda). $$ It turns out that $H$ depends only on the limit of the sequence $(\lambda_n/(\lambda_1+\dots+\lambda_n))$ and the behaviour of the mean $\mathscr{D}$ near zero.