float ideal_theta(float theta,
                  const size_t size,
                  const Data data[size],
                  const Label label[size]) {
    size_t index = get_closest_index(theta, data);

    for (size_t i = index; f_theta(data[i], theta) != label[i] && i >= 0; i--)
        theta = data[i] - 1;

    for (size_t i = index + 1; f_theta(data[i], theta) != label[i] && i < size; i++)
        theta = data[i] + 1;

    return theta;
}