/**
* Prevent adding a cycle.
*
* @param type $from_id
* @param type $to_id
*/
function addLink($from_id, $to_id)
{
$sub = $this->subGraph(array($to_id));
$p = $sub->getParticipants();
if (in_array($from_id, $p)) {
throw new \Exception("Cannot add Cycle '{$from_id}' -> '{$to_id}' to " . $this);
} else {
parent::addLink($from_id, $to_id);
}
}
/**
* Builds a reversed graph without data elements or multigraph.
*
* By reversing a graph one can easily add a root or do other calculations.
* This method is a helper utility.
*
* Note: It is of no use to reverse a Graph.
* Note: data items especially link data is semantic useless when reversed.
*
* @return DirectedGraph
* @see DirectedGraph::addRoot
*
*/
public function getReversedGraph()
{
$g = new DirectedGraph();
foreach (array_keys($this->_list) as $from_id) {
$g->addNode($from_id);
foreach ($this->getLinks($from_id) as $to_id) {
$g->addLink($to_id, $from_id);
}
}
return $g;
}