“…However, there is a metric structure compatible with this topology called Wasserstein distance, which arises from the field of optimal transport (see, e.g., Santambrogio, 2015;Villani, 2003). The Wasserstein distance has attracted a lot of interest recently and has gained a lot of popularity in various fields (e.g., Boissard, Le Gouic, & Loubes, 2015;Burger, Franek, & Schönlieb, 2012;Irpino & Verde, 2008;Ni, Bresson, Chan, & Esedoglu, 2009;Piccoli & Rossi, 2014).…”