/**
 * Rastrigin.java - Stochastic local search implementation of
 * a Rastrigin function search state.
 * See http://cs.gettysburg.edu/~tneller/resources/sls/ for details.
 *
 * @author Todd Neller
 * @version 1.0
 *

Copyright (C) 2005 Todd Neller

This program is free software; you can redistribute it and/or
modify it under the terms of the GNU General Public License
as published by the Free Software Foundation; either version 2
of the License, or (at your option) any later version.

This program is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
GNU General Public License for more details.

Information about the GNU General Public License is available online at:
  http://www.gnu.org/licenses/
To receive a copy of the GNU General Public License, write to the Free
Software Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA
02111-1307, USA.

 */

public class Rastrigin implements State {
	public static final double STDDEV = .05;
	public static java.util.Random random = new java.util.Random();
	public double x;
	public double y;
	public double prevX;
	public double prevY;

	public Rastrigin() {
		this(10.0, 10.0);
	}

	public Rastrigin(double x, double y) {
		this.x = x;
		this.y = y;
		prevX = x;
		prevY = y;
	}

	public void step() {
		prevX = x;
		prevY = y;
		x += STDDEV * random.nextGaussian();
		y += STDDEV * random.nextGaussian();
	}

	public void undo() {
		x = prevX;
		y = prevY;
	}

	public double energy() {
		return x * x + y * y - Math.cos(18 * x) 
		- Math.cos(18 * y) + 2;
	}

	public Object clone() {
		Rastrigin copy = new Rastrigin(x, y);
		copy.prevX = prevX;
		copy.prevY = prevY;
		return copy;
	}

	public String toString() {
		return "(" + x + ", " + y + ")";
	}

}