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<?php
namespace Graphp\Algorithms;
use Fhaculty\Graph\Graph;
/**
* Basic algorithms for working with the (total) weight of a Graph/Walk
*
* A weighted graph associates a label (weight) with every edge in the graph.
* Sometimes the word cost is used instead of weight. The term network is a
* synonym for a weighted graph.
*
* @link http://en.wikipedia.org/wiki/Glossary_of_graph_theory#Weighted_graphs_and_networks
*/
class Weight extends BaseDual
{
/**
* checks whether this graph has any weighted edges
*
* edges usually have no weight attached. a weight explicitly set to (int) 0
* will be considered as 'weighted'.
*
* @return bool
* @uses Edge::getWeight()
*/
public function isWeighted()
{
foreach ($this->set->getEdges() as $edge) {
if ($edge->getWeight() !== NULL) {
return true;
}
}
return false;
}
/**
* get total weight of graph (sum of weight of all edges)
*
* edges with no weight assigned will evaluate to weight (int) 0. thus an
* unweighted graph (see isWeighted()) will return total weight of (int) 0.
*
* returned weight can also be negative or (int) 0 if edges have been
* assigned a negative weight or a weight of (int) 0.
*
* @return float total weight
* @see self::isWeighted()
* @uses Edge::getWeight()
*/
public function getWeight()
{
$weight = 0;
foreach ($this->set->getEdges() as $edge) {
$w = $edge->getWeight();
if ($w !== NULL) {
$weight += $w;
}
}
return $weight;
}
/**
* get minimum weight assigned to all edges
*
* minimum weight is often needed because some algorithms do not support
* negative weights or edges with zero weight.
*
* edges with NO (null) weight will NOT be considered for the minimum weight.
*
* @return float|NULL minimum edge weight or NULL if graph is not weighted or empty
* @uses Edge::getWeight()
*/
public function getWeightMin()
{
$min = NULL;
foreach ($this->set->getEdges() as $edge) {
$weight = $edge->getWeight();
if ($weight !== null && ($min === NULL || $weight < $min)) {
$min = $weight;
}
}
return $min;
}
/**
* get total weight of current flow (sum of all edges flow(e) * weight(e))
*
* @return float
* @see Graph::getWeight() to just get the sum of all edges' weights
* @uses Edge::getFlow()
* @uses Edge::getWeight()
*/
public function getWeightFlow()
{
$sum = 0;
foreach ($this->set->getEdges() as $edge) {
$sum += $edge->getFlow() * $edge->getWeight();
}
return $sum;
}
}
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