RsBundle  Diff

    where
        Self: 'a,
        I: IntoIterator<Item = (Real, &'a Vec<DVector>)>,
    {
        let mut x: Vec<DVector>;
        let mut it = aggregates.into_iter();
        if let Some((alpha, y)) = it.next() {
            x = y.into_iter().map(|yi| yi.scaled(alpha)).collect();
            x = y.iter().map(|yi| yi.scaled(alpha)).collect();
        } else {
            return vec![];
        }

        for (alpha, y) in it {
            for i in 0..x.len() {
                x[i].add_scaled(alpha, &y[i]);