在阵列内部创建数组时出错

Question

我收到此错误：

syntax error, unexpected ',', expecting ']' 

我的代码有问题吗？

class Represent_Graph_Adj_Matrix {
    private $vertices;
    private $adj_matrix = [];

    public function __construct($v) {
        $this->vertices  = $v;
        $this->adj_matrix  = [[$this->vertices + 1],[$this->vertices + 1]];
        var_dump($this->adj_matrix);
    }

    public function makeEdge($to = array(), $from = array(), $edge) {

        try {
            $this->adj_matrix[$to, $from] = $edge; // This is the line of the error
        }
        catch(Exception $e) {
            echo "Vertics does not exists <br>";
        }
    }

    public function getEdge($to, $from) {
        try {
            return $this->adj_matrix[$to][$from];
        }

        catch(Exception $e) {
            echo "Vertics does not exists <br>";
        }

        return -1;
    }

}

你们有些人可以告诉我，导致我的代码出错的原因是什么？
我在我的代码中指出了我的错误行..

拜托，我需要你的帮助.. 谢谢..