Function party_mta_sum 

pub fn party_mta_sum(
    i: usize,
    ks: &[Scalar],
    xs: &[Scalar],
    alphas: &[Vec<Scalar>],
    betas: &[Vec<Scalar>],
) -> Scalar

Party i’s total MtA adjustment: delta_i = k_i x_i + sum_{j != i} (alphas[j][i] + betas[i][j]).