- fixing the lic

- applying patches submitted by David Dixon-Peugh:

I've moved some over.  (Its still in the org/apache/commons/graph
package.)

I added a package "algo" off of the graph package.  This is designed
to hold various graph algorithms.  Graphs have lots of neet things
you can do with them, unfortunately, they don't really fit neatly
into a nice OO design.  (At least I can't see a good connection.)

Changes:

Edge.java
WeightedEdge.java
(org/apache/commons/graph)

These two classes were changed to implement Comparable.  This allows
them to be sorted, and to be dropped into a PriorityQueue.

New Files:

DirectedGraph.java
UndirectedGraph.java
(org/apache/commons/graph)

There are some algorithms which demand either Directed or Undirected
graphs.  These classes allow us to have static type checking for those
algorithms.


Label.java
(org/apache/commons/graph)

There are many algorithms in graph theory which require a marking of
groups.  This label basically has some pointers which it snaps whenever
it is referenced.  It brings running times of some algorithms down close
to O(V + E) rather than O(VlgV + E).


MinimumSpanningForest.java
(org/apache/commons/graph/algo)

This file implements a MinimumSpanningForest algorithm over any graphs.
It uses a PriorityQueue from org/apache/commons/collection.


Sort.java
(org/apache/commons/graph/algo)

This file implements a Topological Sort on directed graphs.  It has some
problems if there is a back edge in the graph.  (Currently it ignores
back edges.  I hope to have it throw a BackEdgeException in the future.)


BackEdges.java
(org/apache/commons/graph/algo)

This file identifies back edges in a Directed Graph, when starting from
a particular vertex.


GraphException.java
BackEdgeException.java
(org/apache/commons/graph/exception)

These are basic exceptions that can be thrown from the graph package.


TestBackEdges.java
TestSort.java
TestMinimumSpanningTree.java

These are JUnit tests for the algorithms provided in this package.
No tests are provided for the Exceptions, Label, Directed and Undirected
classes  (Although Label really should have one.  If Label isn't
working, you get some really nasty bugs.)

--------------------------

Well, this should keep you busy for a while.

Let me know if there are any changes you would like me to make.

DDP

PR:
Obtained from:
Submitted by:
Reviewed by:


git-svn-id: https://svn.apache.org/repos/asf/jakarta/commons/sandbox/graph/trunk@144589 13f79535-47bb-0310-9956-ffa450edef68

src/java/org/apache/commons/graph/GraphAlgorithms.java

@@ -26,12 +26,12 @@ package org.apache.commons.graph;
  *    if and wherever such third-party acknowledgments normally appear.
  *
  * 4. The names "Apache" and "Apache Software Foundation" and
- *    "Apache BCEL" must not be used to endorse or promote products
+ *    "Commons" must not be used to endorse or promote products
  *    derived from this software without prior written permission. For
  *    written permission, please contact apache@apache.org.
  *
  * 5. Products derived from this software may not be called "Apache",
- *    "Apache BCEL", nor may "Apache" appear in their name, without
+ *    "Commons", nor may "Apache" appear in their name, without
  *    prior written permission of the Apache Software Foundation.
  *
  * THIS SOFTWARE IS PROVIDED ``AS IS'' AND ANY EXPRESSED OR IMPLIED
@@ -55,11 +55,13 @@ package org.apache.commons.graph;
  */
 
 import java.util.*;
+import org.apache.commons.graph.algo.*;
+import org.apache.commons.graph.exception.*;
 
 /**
  * Collection of graph algorithms such as transposeGraph.
  *
- * @version $Id: GraphAlgorithms.java,v 1.2 2001/12/02 18:07:18 jvanzyl Exp $
+ * @version $Id: GraphAlgorithms.java,v 1.3 2002/01/16 20:38:28 jvanzyl Exp $
  * @author  <A HREF="http://www.inf.fu-berlin.de/~dahm">M. Dahm</A>
  */
 public abstract class GraphAlgorithms 
@@ -67,11 +69,8 @@ public abstract class GraphAlgorithms
   /**
    * Compute the inverse of a graph, i.e. with all edges reverted
    */
-  public static final Graph transposeGraph(Graph g) {
-    if(!g.isDirected())
-      throw new GraphError("Can only transpose directed graphs");
-
-    Graph graph = new Graph(true);
+  public static final Graph transposeGraph(DirectedGraph g) {
+    DirectedGraph graph = new DirectedGraph();
 
     for(Iterator i=g.getVertices().iterator(); i.hasNext();)
       graph.addVertex((Vertex)i.next());
@@ -85,6 +84,52 @@ public abstract class GraphAlgorithms
     return graph;
   }
 
+    /**
+     * Get a Minimum Spanning Forest from a graph.
+     */
+    public static MinimumSpanningForest 
+	getMinimumSpanningForest( Graph g ) {
+	return MinimumSpanningForest.getMSF( g );
+    }
+
+    public static MinimumSpanningForest 
+	getMinimumSpanningForest( Graph g, boolean isMin ) {
+	return MinimumSpanningForest.getMSF( g, isMin );
+    }
+
+    public static MinimumSpanningForest 
+	getMSF( Graph g ) {
+	return MinimumSpanningForest.getMSF( g );
+    }
+
+    public static MinimumSpanningForest 
+	getMSF( Graph g, boolean isMin ) {
+	return MinimumSpanningForest.getMSF( g, isMin );
+    }
+
+    /**
+     * Perform a Topological Sort on a Directed
+     * graph.
+     *
+     * Should throw BackEdgeException if it is not a DAG.
+     */
+    public static List topoSort( DirectedGraph g ) {
+	return Sort.getInstance().topologicalSort( g );
+    }
+    public static List topologicalSort( DirectedGraph g ) {
+	return Sort.getInstance().topologicalSort( g );
+    }
+
+    /**
+     * Identify all backedges in a directed graph
+     * when starting from a particular vertex.
+     */
+    public static Set getBackEdges( DirectedGraph g, Vertex start )
+	throws BackEdgeException
+    {
+	return BackEdges.getInstance().getBackEdges( g, start );
+    }
+
   /**
    * Test whether the SCC g is a loop.
    *