MathPHP\Probability\Distribution\Continuous\ChiSquared::PDF PHP Метод

    public static function PDF($x, int $k)
    {
        Support::checkLimits(self::LIMITS, ['x' => $x, 'k' => $k]);
        // Numerator
        $x⁽ᵏ／²⁾⁻¹ = $x ** ($k / 2 - 1);
        $ℯ⁻⁽ˣ／²⁾ = exp(-($x / 2));
        // Denominator
        $２ᵏ／² = 2 ** ($k / 2);
        $Γ⟮k／2⟯ = Special::Γ($k / 2);
        return $x⁽ᵏ／²⁾⁻¹ * $ℯ⁻⁽ˣ／²⁾ / ($２ᵏ／² * $Γ⟮k／2⟯);
    }