php matrix determinant

determinant.php

<?php

$matrix = [
    1, 1, 1, 1,
    4, 3, 2, 1,
    2, 3, 4, 1,
    3, 4, 3, 1
];

require 'Matrix.php';

$matrix = (new Matrix(4, 4))->load($matrix);

echo $matrix->det();

Matrix.php

<?php

class Matrix
{
    private $rows = 0;
    private $cols = 0;

    private $data = null;

    public function __construct($rows, $cols)
    {
        $this->rows = $rows;
        $this->cols = $cols;
    }

    public function load($data)
    {
        if (count($data) === $this->rows * $this->cols) {
            $this->data = $data;
        }
        else {
            $this->rows = 0;
            $this->cols = 0;
        }

        return $this;
    }

    public function getLinearIndex($i, $j)
    {
        return $this->cols * $i + $j;
    }

    public function get($i, $j)
    {
        $index = $this->getLinearIndex($i, $j);
        return isset($this->data[$index]) ? $this->data[$index] : null;
    }

    public function getAlgebraicExtension($ci, $cj)
    {
        $matrix = [];
        for ($i = 0; $i < $this->rows; $i++) {
            if ($i === $ci) continue;
            for ($j = 0; $j < $this->cols; $j++) {
                if ($j === $cj) continue;
                $matrix[] = $this->get($i, $j);
            }
        }
        return $matrix;
    }

    public function det()
    {
        $s = 0;

        if ($this->rows === 2 && $this->cols === 2) {
            return $this->get(0, 0) * $this->get(1, 1) - $this->get(1, 0) * $this->get(0, 1);
        }

        for ($j = 0; $j < $this->cols; $j++) {
            $matrix = (new Matrix($this->rows - 1, $this->cols - 1))->load($this->getAlgebraicExtension(0, $j));
            $s += $this->get(0, $j) * pow(-1, $j) * $matrix->det();
        }

        return $s;
    }
}