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AIMA-Java Core Algorithms from the book Artificial Intelligence a Modern Approach 3rd Ed.

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package aima.core.search.informed;

import aima.core.search.framework.Node;
import aima.core.search.framework.evalfunc.HeuristicFunction;
import aima.core.search.framework.evalfunc.PathCostFunction;

/**
 * Artificial Intelligence A Modern Approach (3rd Edition): page 93.

 * 

 * The most widely known form of best-first search is called A* search
 * (pronounced "A-star search"). It evaluates nodes by combining g(n), the cost
 * to reach the node, and h(n), the cost to get from the node to the goal:

 * 
 *  *        f(n) = g(n) + h(n).
 * 
 * 
 * @author Ciaran O'Reilly
 * @author Mike Stampone
 * @author Ruediger Lunde
 */
public class AStarEvaluationFunction extends HeuristicEvaluationFunction {

	private PathCostFunction gf;

	public AStarEvaluationFunction(HeuristicFunction hf) {
		this.hf = hf;
		this.gf = new PathCostFunction();
	}

	/** Note: Do not forget to heuristic function before starting the search! */
	public AStarEvaluationFunction() {
		this.gf = new PathCostFunction();
	}

	/**
	 * Returns g(n) the cost to reach the node, plus h(n) the
	 * heuristic cost to get from the specified node to the goal.
	 * 
	 * @param n
	 *            a node
	 * @return g(n) + h(n)
	 */
	@Override
	public double f(Node n) {
		// f(n) = g(n) + h(n)
		return gf.g(n) + hf.h(n.getState());
	}
}