BMI.java

package CFM;


/*
 * Balanced Mutual Information (BMI)
 * calcola il grado di associazione tra due termini
 */
public class BMI implements CorrelationFunction{
	
	private double beta;
	private static final double def_beta=0.51f;
	private static PMI mi = new PMI();
	
	public BMI(){
		this(def_beta);
	}
	
	public BMI(double b){
		this.beta=b;
	}
	
	public double calculateCorrelation(double p_x, double p_y, double p_x_y) {
		double p_nx_ny	= 1 - (p_x + p_y - p_x_y); 	// Pr(!x,!y)
		double p_x_ny	= p_x - p_x_y;     			// Pr(x, !y)
		double p_nx_y	= p_y - p_x_y;				// Pr(!x, y)
		double p_nx		= 1 - p_x;					// Pr(!x)
		double p_ny		= 1 - p_y;					// Pr(!y)
		double mi_x_y, mi_nx_ny, mi_x_ny, mi_nx_y;
		double bmi;
		
		
		mi_x_y = mi.calculateCorrelation(p_x, p_y, p_x_y);
		
		mi_nx_ny = mi.calculateCorrelation(p_nx, p_ny, p_nx_ny);
		
		mi_x_ny = mi.calculateCorrelation(p_x, p_ny, p_x_ny);
		mi_nx_y = mi.calculateCorrelation(p_nx, p_y, p_nx_y);

		bmi = beta * ( p_x_y * mi_x_y + p_nx_ny * mi_nx_ny)
				- (1 - beta) * ( p_x_ny * mi_x_ny + p_nx_y * mi_nx_y);

		
		return bmi;
	}

}