Improve documentation

Author: clue

src/MinimumSpanningTree/Base.php

@@ -4,28 +4,51 @@
 
 use Fhaculty\Graph\Algorithm\Base as AlgorithmBase;
 use Fhaculty\Graph\Set\Edges;
+use Fhaculty\Graph\Exception\UnexpectedValueException;
+use Fhaculty\Graph\Edge\Directed as EdgeDirected;
 
+/**
+ * Abstract base class for minimum spanning tree (MST) algorithms
+ *
+ * A minimum spanning tree of a graph is a subgraph that is a tree and connects
+ * all the vertices together while minimizing the total sum of all edges'
+ * weights.
+ *
+ * A spanning tree thus requires a connected graph (single connected component),
+ * otherwise we can span multiple trees (spanning forest) within each component.
+ * Because a null graph (a Graph with no vertices) is not considered connected,
+ * it also can not contain a spanning tree.
+ *
+ * @link http://en.wikipedia.org/wiki/Minimum_Spanning_Tree
+ * @link http://en.wikipedia.org/wiki/Spanning_Tree
+ * @link http://mathoverflow.net/questions/120536/is-the-empty-graph-a-tree
+ */
 abstract class Base extends AlgorithmBase
 {
     /**
      * create new resulting graph with only edges on minimum spanning tree
      *
      * @return Graph
-     * @uses AlgorithmMst::getEdges()
+     * @uses self::getGraph()
+     * @uses self::getEdges()
      * @uses Graph::createGraphCloneEdges()
      */
     public function createGraph()
     {
-        // Copy Graph
         return $this->getGraph()->createGraphCloneEdges($this->getEdges());
     }
 
-    abstract protected function getGraph();
-
     /**
      * get all edges on minimum spanning tree
      *
      * @return Edges
      */
     abstract public function getEdges();
+
+    /**
+     * return reference to current Graph
+     *
+     * @return Graph
+     */
+    abstract protected function getGraph();
 }