Generalized H\"older's inequality on Morrey spaces

The aim of this paper is to present necessary and sufficient conditions for generalized H\"{o}lder's inequality on generalized Morrey spaces. We also obtain similar results on weak Morrey spaces and on generalized weak Morrey spaces. The necessary and sufficient conditions for the generalized H\"{o}lder's inequality on these spaces are obtained through estimates for characteristic functions of balls in $\mathbb{R}^d$.