MathPHP\LinearAlgebra\Matrix::trace PHP Method

    public function trace()
    {
        if (!$this->isSquare()) {
            throw new Exception\MatrixException('trace only works on a square matrix');
        }
        $m = $this->m;
        $tr⟮A⟯ = 0;
        for ($i = 0; $i < $m; $i++) {
            $tr⟮A⟯ += $this->A[$i][$i];
        }
        return $tr⟮A⟯;
    }