X-Git-Url: http://info.iut-bm.univ-fcomte.fr/pub/gitweb/simgrid.git/blobdiff_plain/ff6cb26262ba25fefdf1265628265a75d790ebd6..200986a368bbbbb5df459d43cbc7f5ef3d7678db:/contrib/psg/src/peersim/util/MomentStats.java

diff --git a/contrib/psg/src/peersim/util/MomentStats.java b/contrib/psg/src/peersim/util/MomentStats.java
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+/*
+ * Copyright (c) 2003-2005 The BISON Project
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU Lesser General Public License version 2 as
+ * published by the Free Software Foundation.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU Lesser General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public License
+ * along with this program; if not, write to the Free Software
+ * Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
+ *
+ */
+
+package peersim.util;
+
+/**
+ * This class provides extended statistical informations about the inspected 
+ * distribution. In particular, it provides functions to compute the skewness
+ * (the 3rd degree moment) and the kurtosis (4th degree moment).
+ *
+ * @author  Gian Paolo Jesi
+ */
+public class MomentStats extends IncrementalStats {
+    
+    private double cubicsum, quadsum; // incremental sums
+    
+    /** Calls {@link #reset} */
+    public MomentStats() {
+    	reset();
+    }
+    
+    public void reset() {
+        super.reset();
+        cubicsum = quadsum = 0.0;
+    }
+    
+    public void add(double item, int k) {
+        for(int i=0; i<k; ++i)
+	{
+        	super.add(item,1);
+        	cubicsum += item * item * item;
+        	quadsum += item * cubicsum;
+    	}
+    }
+   
+    /** Outputs on a single line the superclass statistics postfixed by the 
+     * current skewness and kurtosis.
+     */
+    public String toString() {
+        return super.toString()+" "+getSkewness()+" "+getKurtosis();
+    }
+    
+    /** Computes the skewness on the node values distribution and 
+     * returns the asymmetry coefficient. It gives an indication about the 
+     * distribution symmetry compared to the average.
+     *
+     *@return The skewness value as a double.
+     */ 
+    public double getSkewness() {
+        int n = this.getN();
+        double m3 = (((double)n) / (n-1)) * (cubicsum/n - Math.pow(getAverage(), 3) );
+        return ( m3 / Math.pow(getStD(), 3 ) );
+    }
+    
+    /** Computes the kurtosis on the node values distribution and 
+     *  returns the flatness coefficient. It gives an indication about the 
+     *  distribution sharpness or flatness.
+     *
+     * @return The kurtosis momentus value as a double.
+     */ 
+    public double getKurtosis(){
+        int n = this.getN();
+        double m4 = (((double)n) / (n-1)) * (quadsum/n - Math.pow(getAverage(), 4) );
+        return ( m4 / Math.pow(getStD(), 4) )-3;
+    }
+
+}