/**
* Inserts the given edge into this graph.
*
* @param object Edge $edge The edge to insert.
*/
protected function insertEdge(Edge $edge)
{
$v = $edge->getV0()->getNumber();
$w = $edge->getV1()->getNumber();
if ($this->matrix[array($v, $w)] !== NULL) {
throw new ArgumentError();
}
if ($v == $w) {
throw new ArgumentError();
}
$this->matrix[array($v, $w)] = $edge;
$this->matrix[array($w, $v)] = $edge;
++$this->numberOfEdges;
}