PMI.java

package CFM;


/*
 * Mutual Information
 * metodo che calcola la dipendenza tra due entit�
 */
public class PMI implements CorrelationFunction{
	private static final int num = 2048;
	

	
	public double calculateCorrelation(double p_x, double p_y, double p_x_y) {
		
		int isZero = new Double(p_x_y).compareTo(0.0);
		int isOne = new Double(p_x_y).compareTo(1.0);
		
		if (isZero == 0)
			return -num;
		
		if (isOne == 0)
			return num;
		
		double log2 = Math.log(2);
		/*double ex = - p_x * Math.log(p_x)/log2;
		double ey = - p_y * Math.log(p_y)/log2;
		double exy = - p_x_y * Math.log(p_x_y)/log2;
		
		return  ex + ey - exy;*/
		
		return  (Math.log(p_x_y) - Math.log(p_x) - Math.log(p_y))/Math.log(2);
	}
	
	

}