MathPHP\Statistics\Regression\Methods\LeastSquares::regressionVariance PHP 메소드

    public function regressionVariance($x)
    {
        $X = $this->createDesignMatrix($x);
        $⟮XᵀX⟯⁻¹ = $this->⟮XᵀX⟯⁻¹;
        $M = $X->multiply($⟮XᵀX⟯⁻¹)->multiply($X->transpose());
        return $M[0][0];
    }