samer@0: /*
samer@0:  *	Copyright (c) 2000, Samer Abdallah, King's College London.
samer@0:  *	All rights reserved.
samer@0:  *
samer@0:  *	This software is provided AS iS and WITHOUT ANY WARRANTY; 
samer@0:  *	without even the implied warranty of MERCHANTABILITY or 
samer@0:  *	FITNESS FOR A PARTICULAR PURPOSE.
samer@0:  */
samer@0: 
samer@0: package samer.maths.random;
samer@0: import  samer.core.types.*;
samer@0: import  java.util.*;
samer@0: 
samer@0: /*
samer@0:  *		Generates random numbers from a single-sider power-law 
samer@0:  *		with a lower cut-off, but no upper cut-off. The
samer@0:  *		exponent must therefore be strictly less than 1.
samer@0:  */
samer@0: public class PowerLaw extends BaseRandom implements Observer
samer@0: {
samer@0: 	VDouble min = new VDouble("min",1);
samer@0: 	VDouble D   = new VDouble("exponent",1);
samer@0: 	double  a, b;
samer@0: 
samer@0: 	public void dispose() { min.dispose(); D.dispose(); }
samer@0: 	public double next() { return a*Math.pow(rnd.nextDouble(),b); }
samer@0: 
samer@0: 	public PowerLaw() 
samer@0: 	{
samer@0: 		min.addObserver(this);
samer@0: 		D.addObserver(this);
samer@0: 		update(null,null);
samer@0: 	}
samer@0: 
samer@0: 	public void update(Observable o, Object oo) {
samer@0: 		a=min.value;
samer@0: 		b=-1/D.value;
samer@0: 	}
samer@0: }