svn commit: r1305120 - /commons/sandbox/graph/trunk/src/main/java/org/apache/commons/graph/elo/EloRankingCalculator.java

[si...@apache.org]

Author: simonetripodi
Date: Sun Mar 25 20:33:17 2012
New Revision: 1305120

URL: http://svn.apache.org/viewvc?rev=1305120&view=rev
Log:
first spike implementation of the core ELO evaluator algorithm

Added:
    commons/sandbox/graph/trunk/src/main/java/org/apache/commons/graph/elo/EloRankingCalculator.java   (with props)

Added: commons/sandbox/graph/trunk/src/main/java/org/apache/commons/graph/elo/EloRankingCalculator.java
URL: http://svn.apache.org/viewvc/commons/sandbox/graph/trunk/src/main/java/org/apache/commons/graph/elo/EloRankingCalculator.java?rev=1305120&view=auto
==============================================================================
--- commons/sandbox/graph/trunk/src/main/java/org/apache/commons/graph/elo/EloRankingCalculator.java (added)
+++ commons/sandbox/graph/trunk/src/main/java/org/apache/commons/graph/elo/EloRankingCalculator.java Sun Mar 25 20:33:17 2012
@@ -0,0 +1,111 @@
+package org.apache.commons.graph.elo;
+
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ *   http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing,
+ * software distributed under the License is distributed on an
+ * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+ * KIND, either express or implied.  See the License for the
+ * specific language governing permissions and limitations
+ * under the License.
+ */
+
+import static java.lang.Math.pow;
+
+import org.apache.commons.graph.DirectedGraph;
+import org.apache.commons.graph.Mapper;
+
+final class EloRankingCalculator<P>
+{
+
+    private static final double DEFAULT_POW_BASE = 10;
+
+    private static final double DEFAULT_DIVISOR = 400;
+
+    private static final int DEFAULT_K_FACTOR = 32;
+
+    private final DirectedGraph<P, GameResult> tournamentGraph;
+
+    private final Mapper<P, Double> playerRanking;
+
+    private final int kFactor;
+
+    public EloRankingCalculator( DirectedGraph<P, GameResult> tournamentGraph,
+                                 Mapper<P, Double> playerRanking, int kFactor )
+    {
+        this.tournamentGraph = tournamentGraph;
+        this.playerRanking = playerRanking;
+        this.kFactor = kFactor;
+    }
+
+    // TODO find a way to improve performances, this impl is just a spike
+    public void calculateRate()
+    {
+        for ( P player : tournamentGraph.getVertices() )
+        {
+            for ( P opponent : tournamentGraph.getOutbound( player ) )
+            {
+                GameResult gameResult = tournamentGraph.getEdge( player, opponent );
+                evaluateMatch( player, gameResult, opponent );
+            }
+        }
+    }
+
+    private boolean evaluateMatch( P playerA, GameResult gameResult, P playerB )
+    {
+        double qA = calculateQFactor( playerA );
+        double qB = calculateQFactor( playerB );
+
+        double eA = calculateEFactor( qA, qB );
+        double eB = calculateEFactor( qB, qA );
+
+        double sA;
+        double sB;
+        switch ( gameResult )
+        {
+            case WIN:
+                sA = 1;
+                sB = 0;
+                break;
+
+            case DRAW:
+                sA = 0.5;
+                sB = 0.5;
+                break;
+
+            default: // should not happen
+                throw new IllegalArgumentException( "Input GameResult not accepted" );
+        }
+
+        updateRanking( playerA, kFactor, sA, eA );
+        updateRanking( playerB, kFactor, sB, eB );
+        return true;
+    }
+
+    private double calculateQFactor( P player )
+    {
+        double ranking = playerRanking.map( player );
+        return pow( DEFAULT_POW_BASE, ranking / DEFAULT_DIVISOR);
+    }
+
+    private static double calculateEFactor( double qA, double qB )
+    {
+        return qA / (qA + qB);
+    }
+
+    private void updateRanking( P player, double kFactor, double sFactor, double eFactor )
+    {
+        double newRanking = playerRanking.map( player ) + ( kFactor * ( sFactor - eFactor ) );
+        // TODO find a way to set the new calculated ranking to the current player
+    }
+
+}

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