Function generational_distance 

pub fn generational_distance(set: &[Vec<f64>], reference: &[Vec<f64>]) -> f64

The generational distance of set from reference: the mean, over the points of set, of the Euclidean distance to the nearest point of reference. It is Deb et al.’s (2002) convergence metric Υ (§IV-B, p. 188), and pymoo’s GD: zero when every point lies on the reference. NaN for an empty set or reference.