vec4 L(float t) {
        vec4 rr(0, 0, 0);
        for (int i = 0; i < cps.size(); i++) rr += cps[i] * l_base(i, t);
        return rr;
    }

    float l_base(int i, float t) {
        float Li = 1.0f;
        for (int j = 0; j < cps.size(); j++)
            if (j != i) Li *= (t - ts[j]) / (ts[i] - ts[j]);
        return Li;
    }

    vec4 dL(float t) {
        vec4 rr(0, 0, 0);
        for (int i = 0; i < cps.size(); i++) rr += cps[i] * dl_base(i, t);
        return rr;
    }

    float dl_base(int i, float t) {
        float dl = 0.0f;
        for (int j = 0; j < cps.size(); j++)
            if (j != i) dl += 1 / (t - ts[j]);
        dl *= l_base(i, t);
        return dl;
    }