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 * Copyright (c) 2014 Opt4J
 *
 * Permission is hereby granted, free of charge, to any person obtaining a copy
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package org.opt4j.optimizers.sa;

import org.opt4j.core.start.Constant;

import com.google.inject.Inject;

/**
 * 
 * The {@link CoolingScheduleExponential} is a {@link CoolingSchedule} for the
 * {@link SimulatedAnnealing}.
 * 
 * 
 * {@code tn - final temperature}

 * {@code t0 - initial temperature}

 * {@code i - current iteration}

 * {@code n - maximal number of iterations} 

 * {@code a - alpha value}

 * 
 * 
 * The current temperature is calculated by {@code tn + t0 * a^i}.
 * 
 * 
 * 
 * 
 * @author lukasiewycz
 * 
 */
public class CoolingScheduleExponential implements CoolingSchedule {

	protected final double t0;

	protected final double tn;

	protected final double alpha;

	/**
	 * Constructs a new {@link CoolingScheduleExponential}.
	 * 
	 * @param t0
	 *            the initial temperature (using namespace
	 *            {@link CoolingSchedule})
	 * @param tn
	 *            the final temperature (using namespace {@link CoolingSchedule}
	 *            ) )
	 * @param alpha
	 *            the alpha value
	 */
	@Inject
	public CoolingScheduleExponential(@Constant(value = "t0", namespace = CoolingSchedule.class) double t0,
			@Constant(value = "tn", namespace = CoolingSchedule.class) double tn,
			@Constant(value = "alpha", namespace = CoolingScheduleExponential.class) double alpha) {
		this.t0 = t0;
		this.tn = tn;
		this.alpha = alpha;
	}

	/*
	 * (non-Javadoc)
	 * 
	 * @see org.opt4j.optimizer.sa.CoolingSchedule#getTemperature(int, int)
	 */
	@Override
	public double getTemperature(int i, int n) {
		return tn + t0 * Math.pow(alpha, i);
	}

}