svn commit: r1174740 - /labs/openelo/src/main/java/org/apache/openelo/RankingCalculator.java

[si...@apache.org]

Author: simonetripodi
Date: Fri Sep 23 13:23:06 2011
New Revision: 1174740

URL: http://svn.apache.org/viewvc?rev=1174740&view=rev
Log:
first checkin of RankingCalculator class

Added:
    labs/openelo/src/main/java/org/apache/openelo/RankingCalculator.java   (with props)

Added: labs/openelo/src/main/java/org/apache/openelo/RankingCalculator.java
URL: http://svn.apache.org/viewvc/labs/openelo/src/main/java/org/apache/openelo/RankingCalculator.java?rev=1174740&view=auto
==============================================================================
--- labs/openelo/src/main/java/org/apache/openelo/RankingCalculator.java (added)
+++ labs/openelo/src/main/java/org/apache/openelo/RankingCalculator.java Fri Sep 23 13:23:06 2011
@@ -0,0 +1,115 @@
+package org.apache.openelo;
+
+/*
+ * 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;
+
+/**
+ *
+ */
+public final class RankingCalculator
+{
+
+    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 int kFactor;
+
+    /**
+     *
+     */
+    public RankingCalculator()
+    {
+        this( DEFAULT_K_FACTOR );
+    }
+
+    /**
+     *
+     *
+     * @param kFactor
+     */
+    public RankingCalculator( int kFactor )
+    {
+        this.kFactor = kFactor;
+    }
+
+    /**
+     *
+     *
+     * @param <I>
+     * @param <N>
+     * @param playerA
+     * @param playerB
+     * @param gameResult
+     */
+    public final <I> void updateRating( Player<I> playerA, Player<I> playerB, GameResult gameResult )
+    {
+        double qA = calculateQFactor( playerA.getRanking() );
+        double qB = calculateQFactor( playerB.getRanking() );
+
+        double eA = calculateEFactor( qA, qB );
+        double eB = calculateEFactor( qB, qA );
+
+        double sA;
+        double sB;
+        switch ( gameResult )
+        {
+            case WIN:
+                sA = 1;
+                sB = 0;
+                break;
+
+            case LOSE:
+                sA = 0;
+                sB = 1;
+                break;
+
+            case DRAW:
+                sA = 0.5;
+                sB = 0.5;
+                break;
+
+            default: // shouldn't happen
+                throw new IllegalArgumentException( "Input GameResult not accepted" );
+        }
+
+        updateRanking( playerA, kFactor, sA, eA );
+        updateRanking( playerB, kFactor, sB, eB );
+    }
+
+    private static double calculateQFactor( double ranking )
+    {
+        return pow( DEFAULT_POW_BASE, ranking / DEFAULT_DIVISOR);
+    }
+
+    private static double calculateEFactor( double qA, double qB )
+    {
+        return qA / (qA + qB);
+    }
+
+    private static <I> void updateRanking( Player<I> player, double kFactor, double sFactor, double eFactor )
+    {
+        player.updateRanking( player.getRanking() + ( kFactor * ( sFactor - eFactor ) ) );
+    }
+
+}

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