public function normalize(float $score, int $alpha=15)
    {
        $normalizedScore = $score/sqrt(($score^2) + $alpha);
        if ($normalizedScore < -1.0) {
            return -1.0;
        } elseif ($normalizedScore > 1.0) {
            return 1.0;
        }
        return $normalizedScore;
    }