RsBundle  Diff

        let mut aggr = primals[0]
            .1
            .iter()
            .map(|x| {
                let mut r = dvec![];
                r.scal(primals[0].0, x);
                r
            })
            .collect::<Vec<_>>();

        for &(alpha, primal) in &primals[1..] {
            for (j, x) in primal.iter().enumerate() {
                aggr[j].add_scaled(alpha, x);
            }
        }