Starting from word embeddings, researchers proposed various ways of aggregating word embedding vectors to obtain efficient sentence-level or documentlevel representations Cheng et al., 2018; Clinchant and Perronnin, 2013; Conneau et al., 2017; Cozma et al., 2018; Fu et al., 2018; <cite>Hill et al., 2016</cite>; Kiros et al., 2015; Kusner et al., 2015; Le and Mikolov, 2014; Shen et al., 2018; Torki, 2018; Zhao et al., 2015; Zhou et al., 2016 Zhou et al., , 2018 .