@Override
    public double fun(double[] w) {
        double f = 0;
        double[] y = prob.y;
        int l = prob.l;
        int w_size = get_nr_variable();
        double d;

        Xv(w, z);

        for (int i = 0; i < w_size; i++)
            f += w[i] * w[i];
        f /= 2;
        for (int i = 0; i < l; i++) {
            d = z[i] - y[i];
            if (d < -p)
                f += C[i] * (d + p) * (d + p);
            else if (d > p) f += C[i] * (d - p) * (d - p);
        }

        return f;
    }