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The Jadex applib BDI package contains ready to use functionalities for BDI agents mostly in form of modules called capabilities.
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package jadex.bdi.planlib.protocols;


import java.util.List;

import jadex.commons.collection.SCollection;

/**
 *  A sample implementation of the IPriceCalculator. Calculates the price for the
 *  next round of an english auction.
 */
public class ExponentialPriceCalculator implements IOfferGenerator
{
	//-------- attributes --------

	/** The negotiation round. */
	protected int round;

	/** The start price. */
	protected double startprice;
	
	/** The limit price. */
	protected double limitprice;

	/** The prices. */
	protected List prices;
	
	/** The variation. */
	protected double variation;

	/** The base (base^round). */
	protected double base;
	
	/** The minimum step width. */
	protected double minstepwidth;
	
	/** Flag indicating if increasing or decreasing prices are calculated. */
	protected boolean increasing;

	//-------- constructors --------

	/**
	 *  Create a new exponential price calculator.
	 *  @param startprice The start price.
	 *  @param limitprice The limit price (min or max) for a auction.
	 *  @param base The base for the exponential function.
	 */
	public ExponentialPriceCalculator(double startprice, double limitprice, double base)
	{
		this(startprice, limitprice, base, 0.0, 0.0);
	}

	/**
	 *  Create a new exponential price calculator.
	 *  @param startprice the start price
	 *  @param limitprice the minimal price for a successful auction
	 *  @param base The base for the exponential function.
	 *  @param variation The variation in percentage (0->1) for the increment.
	 *  	   The increment will be used to adapt the increment by multiplying
	 *  	   it with (+/-) a random value that has maximal the variation
	 *  	   percentage influence, e.g. setting 0.1 will cause the increment
	 *  	   being maximally +/-10% changed.
	 *  @param minstepwidth The minimum step width (a positive value that describes
	 *  	   the minimum price change in each round).
	 */
	public ExponentialPriceCalculator(double startprice, double limitprice,
		double base, double variation, double minstepwidth)
	{
		this.startprice = startprice;
		this.prices = SCollection.createArrayList();
		this.prices.add(Double.valueOf(startprice));
		this.limitprice = limitprice;
		this.base = base;
		this.variation = variation;
		this.minstepwidth = minstepwidth;
		if(minstepwidth<0)
			throw new IllegalArgumentException("Step width need to be > 0.");
		
		this.round = 1;
		this.increasing = limitprice > startprice;
	}
	
	//-------- methods --------

	/**
	 *  Get the price for the current round of this auction.
	 *  @return The price.
	 */
	public Comparable getCurrentOffer()
	{
		double ret;
		if(prices.size() == getRound())
		{
			ret = ((Double)prices.get(getRound()-1)).doubleValue();
		}
		else
		{
			// Exponential growth: price(round) = price(0)*(rate^(+/-)round + var)
			
			double var = (Math.random()-0.5)*2*variation;
			if(increasing)
				ret = (Math.pow(base, round)+var)*startprice;
			else
				ret = (Math.pow(base, -round)+var)*startprice; 
			
			double lastprice = ((Double)prices.get(getRound()-2)).doubleValue();
			
			// Ensure monotony
			if(increasing && retlastprice)
				ret = lastprice-minstepwidth;
						
			// Ensure that price is not out of bounds
			if((increasing && ret>limitprice) || (!increasing && ret1? (Comparable)prices.get(prices.size()-2): null;
	}

	/**
	 *  Get the min price.
	 *  @return The minprice.
	 */
	public Comparable getLimitOffer()
	{
		return Double.valueOf(limitprice);
	}
	
	/**
	 *  Get the start price.
	 *  @return The startprice
	 */
	public Comparable getStartOffer()
	{
		return Double.valueOf(startprice);
	}
	
	/**
	 *  Get the round.
	 *  @return The round.
	 */
	public int getRound()
	{
		return round;
	}
	
	/**
	 *  Increase the round.
	 */
	public void setNextRound()
	{
		round++;
	}
	
	/**
	 *  Main for testing.
	 */
	public static void main(String[] args)
	{
		IOfferGenerator pc = new ExponentialPriceCalculator(100, 10, 1.1, 0.1, 1.0);
		for(int i=0; i<20; i++)
		{
			System.out.println("Price "+i+": "+pc.getCurrentOffer());
			pc.setNextRound();
			if(pc.getLimitOffer().equals(pc.getLastOffer()))
				System.out.println("Limit reached");
		}
		System.out.println();
		
		pc = new ExponentialPriceCalculator(100, 500, 1.1, 0.1, 1.0);
		for(int i=0; i<20; i++)
		{
			System.out.println("Price "+i+": "+pc.getCurrentOffer());
			pc.setNextRound();
			if(pc.getLimitOffer().equals(pc.getLastOffer()))
				System.out.println("Limit reached");
		}
	}
	
}