def velocity_from_coupling(gamma, mu_spt, nu_spt, dt):
    """Estimate velocity field from coupling 

    :param gamma: coupling
    :param mu_spt: support of source measure
    :param nu_spt: support of target measure
    :param dt: time interval 
    """
    return (gamma @ nu_spt - gamma.sum(1).view(-1, 1) * mu_spt)/dt