comparison src/samer/maths/random/PowerLaw.java @ 0:bf79fb79ee13

Initial Mercurial check in.

+/*
+ *	Copyright (c) 2000, Samer Abdallah, King's College London.
+ *	All rights reserved.
+ *
+ *	This software is provided AS iS and WITHOUT ANY WARRANTY; 
+ *	without even the implied warranty of MERCHANTABILITY or 
+ *	FITNESS FOR A PARTICULAR PURPOSE.
+ */
+
+package samer.maths.random;
+import  samer.core.types.*;
+import  java.util.*;
+
+/*
+ *		Generates random numbers from a single-sider power-law 
+ *		with a lower cut-off, but no upper cut-off. The
+ *		exponent must therefore be strictly less than 1.
+ */
+public class PowerLaw extends BaseRandom implements Observer
+{
+	VDouble min = new VDouble("min",1);
+	VDouble D   = new VDouble("exponent",1);
+	double  a, b;
+
+	public void dispose() { min.dispose(); D.dispose(); }
+	public double next() { return a*Math.pow(rnd.nextDouble(),b); }
+
+	public PowerLaw() 
+	{
+		min.addObserver(this);
+		D.addObserver(this);
+		update(null,null);
+	}
+
+	public void update(Observable o, Object oo) {
+		a=min.value;
+		b=-1/D.value;
+	}
+}