Second Wasserstein distance
= Second Wasserstein distance
{title2=$W_2(\mu,\nu)$}
For <probability measure>[probability measures] with finite <second moment>[second moments] on a <metric space>,
$$
W_2(\mu,\nu)^2=\inf\{\mathbb E[\rho(X,Y)^2]:(X,Y)\text{ couples }\mu,\nu\}.
$$