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:  *		Hyperbolic distribution: power law with exponent 1.
samer@0:  *		Integral of pdf diverges in both directions, so we
samer@0:  *		need both upper and lower cut-offs.
samer@0:  */
samer@0: public class BoundedHyperbolic extends BaseRandom implements Observer
samer@0: {
samer@0: 	VDouble min = new VDouble("min",1);
samer@0: 	VDouble max = new VDouble("max",2);
samer@0: 	double  a, b;
samer@0: 
samer@0: 	public void dispose() { min.dispose(); max.dispose(); }
samer@0: 	public double next() { return b*Math.exp(a*rnd.nextDouble()); }
samer@0: 
samer@0: 	public BoundedHyperbolic( double min, double max) 
samer@0: 	{
samer@0: 		this();
samer@0: 		this.min.value = min; this.min.changed();
samer@0: 		this.max.value = max; this.max.changed();
samer@0: 	}
samer@0: 
samer@0: 	public BoundedHyperbolic() 
samer@0: 	{
samer@0: 		min.addObserver(this);
samer@0: 		max.addObserver(this);
samer@0: 		update(null,null);
samer@0: 	}
samer@0: 
samer@0: 	public void update(Observable o, Object oo) {
samer@0: 		a=Math.log(min.value/max.value); 
samer@0: 		b=max.value;
samer@0: 	}
samer@0: }