/**
* Calculate the Moore-Bellman-Ford-Algorithm and get all edges on shortest path for this vertex
*
* @return Edges
* @throws NegativeCycleException if there is a negative cycle
*/
public function getEdges()
{
// start node distance, add placeholder weight
$totalCostOfCheapestPathTo = array($this->vertex->getId() => INF);
// predecessor
$predecessorVertexOfCheapestPathTo = array($this->vertex->getId() => $this->vertex);
// the usal algorithm says we repeat (n-1) times.
// but because we also want to check for loop edges on the start vertex,
// we have to add an additional step:
$numSteps = count($this->vertex->getGraph()->getVertices());
$edges = $this->vertex->getGraph()->getEdges();
$changed = true;
for ($i = 0; $i < $numSteps && $changed; ++$i) {
$changed = $this->bigStep($edges, $totalCostOfCheapestPathTo, $predecessorVertexOfCheapestPathTo);
}
// no cheaper edge to start vertex found => remove placeholder weight
if ($totalCostOfCheapestPathTo[$this->vertex->getId()] === INF) {
unset($predecessorVertexOfCheapestPathTo[$this->vertex->getId()]);
}
// algorithm is done, build graph
$returnEdges = $this->getEdgesCheapestPredecesor($predecessorVertexOfCheapestPathTo);
// Check for negative cycles (only if last step didn't already finish anyway)
// something is still changing...
if ($changed && ($changed = $this->bigStep($edges, $totalCostOfCheapestPathTo, $predecessorVertexOfCheapestPathTo))) {
$cycle = Walk::factoryCycleFromPredecessorMap($predecessorVertexOfCheapestPathTo, $changed, Edges::ORDER_WEIGHT);
throw new NegativeCycleException('Negative cycle found', 0, NULL, $cycle);
}
return $returnEdges;
}
/**
* @expectedException InvalidArgumentException
*/
public function testInvalidPredecessors()
{
$graph = new Graph();
$v1 = $graph->createVertex(1);
Walk::factoryCycleFromPredecessorMap(array(), $v1);
}
