/**
* Searches all vertices for the first negative cycle
*
* @return Walk
* @throws UnderflowException if there's no negative cycle
* @uses AlgorithmSpMooreBellmanFord::getVertices()
*/
public function getCycleNegative()
{
// remember vertices already visited, as they can not lead to a new cycle
$verticesVisited = array();
// check for all vertices
foreach ($this->graph->getVertices()->getMap() as $vid => $vertex) {
// skip vertices already visited
if (!isset($verticesVisited[$vid])) {
// start MBF algorithm on current vertex
$alg = new SpMooreBellmanFord($vertex);
try {
// try to get all connected vertices (or throw new cycle)
foreach ($alg->getVertices()->getIds() as $vid) {
// getting connected vertices succeeded, so skip over all of them
$verticesVisited[$vid] = true;
// no cycle found, check next vertex...
}
// yey, negative cycle encountered => return
} catch (NegativeCycleException $e) {
return $e->getCycle();
}
}
// no more vertices to check => abort
}
throw new UnderflowException('No negative cycle found');
}
