On extropy of past lifetime distribution

Recently Qiu [6] have introduced residual extropy as measure of uncertainty in residual lifetime distributions analogues to residual entropy (see, e.g. [3]). Also, they obtained some properties and applications of that. In this paper, we study the extropy to measure the uncertainty in a past lifetime distribution. This measure of uncertainty is called past extropy. Also it is showed a characterization result about the past extropy of largest order statistics.