Move Vertex::getFlow() to Algorithm\Flow::getFlowVertex()

Author: clue

src/Balance.php

@@ -5,6 +5,7 @@
 use Fhaculty\Graph\Algorithm\BaseGraph;
 use Fhaculty\Graph\Graph;
 use Fhaculty\Graph\Vertex;
+use Fhaculty\Graph\Algorithm\Flow;
 
 /**
  * Basic algorithms for working with the balance of flow graphs
@@ -41,15 +42,17 @@ public function getBalance()
      *
      * @return boolean
      * @see Algorithm\Degree::isBalanced() if you merely want to check indegree=outdegree
-     * @uses Vertex::getFlow()
+     * @uses Flow::getFlowVertex()
      * @uses Vertex::getBalance()
      */
     public function isBalancedFlow()
     {
+        $flow = new Flow($this->graph);
+
         // no need to check for each edge: flow <= capacity (setters already check that)
         // check for each vertex: outflow-inflow = balance
         foreach ($this->graph->getVertices() as $vertex) {
-            if ($vertex->getFlow() !== $vertex->getBalance()) {
+            if ($flow->getFlowVertex($vertex) !== $vertex->getBalance()) {
                 return false;
             }
         }

src/Flow.php

@@ -4,7 +4,9 @@
 
 use Fhaculty\Graph\Algorithm\BaseGraph;
 use Fhaculty\Graph\Edge\Base as Edge;
+use Fhaculty\Graph\Edge\Directed as EdgeDirected;
 use Fhaculty\Graph\Graph;
+use Fhaculty\Graph\Vertex;
 
 /**
  * Basic algorithms for working with flow graphs
@@ -33,4 +35,43 @@ public function hasFlow()
 
         return false;
     }
+
+    /**
+     * Calculates the flow for this Vertex: sum(outflow) - sum(inflow)
+     *
+     * Usually, vertices should have a resulting flow of 0: The sum of flows
+     * entering a vertex must equal the sum of flows leaving a vertex. If the
+     * resulting flow is < 0, this vertex is considered a sink (i.e. there's
+     * more flow into this vertex). If the resulting flow is > 0, this vertex
+     * is considered a "source" (i.e. there's more flow leaving this vertex).
+     *
+     * @param Vertex $vertex
+     * @return float
+     * @throws UnexpectedValueException if they are undirected edges
+     * @see Vertex::getBalance()
+     * @uses Vertex::getEdges()
+     * @uses Edge::getFlow()
+     */
+    public function getFlowVertex(Vertex $vertex)
+    {
+        $sumOfFlow = 0;
+
+        foreach ($vertex->getEdges() as $edge) {
+            if (!($edge instanceof EdgeDirected)) {
+                throw new UnexpectedValueException("TODO: undirected edges not suported yet");
+            }
+
+            // edge is an outgoing edge of this vertex
+            if ($edge->hasVertexStart($vertex)) {
+                // flowing out (flow is "pointing away")
+                $sumOfFlow += $edge->getFlow();
+                // this is an ingoing edge
+            } else {
+                // flowing in
+                $sumOfFlow -= $edge->getFlow();
+            }
+        }
+
+        return $sumOfFlow;
+    }
 }

src/MinimumCostFlow/SuccessiveShortestPath.php

@@ -19,7 +19,6 @@
 class SuccessiveShortestPath extends Base
 {
     /**
-     * @uses Vertex::getFlow()
      * @uses Graph::createGraphClone()
      * @uses AlgorithmResidualGraph::createGraph()
      * @uses AlgorithmSpMooreBellmanFord::getEdgesTo(Vertex $targetVertex)