一种改进的余弦距离测度

<strong><span style="font-size:18px;">/***
 * @author YangXin
 * @info一种改进的余弦距离测度
 */
package unitTen;

import java.util.Collection;
import java.util.Collections;

import org.apache.hadoop.conf.Configuration;
import org.apache.mahout.common.distance.DistanceMeasure;
import org.apache.mahout.common.parameters.Parameter;
import org.apache.mahout.math.CardinalityException;
import org.apache.mahout.math.Vector;

public class MyDistanceMeasure implements DistanceMeasure {

	  @Override
	  public double distance(Vector v1, Vector v2) {
	    if (v1.size() != v2.size()) {
	      throw new CardinalityException(v1.size(), v2.size());
	    }
	    double lengthSquaredv1 = v1.getLengthSquared();
	    double lengthSquaredv2 = v2.getLengthSquared();
	    
	    double dotProduct = v2.dot(v1);
	    
	    double denominator = Math.sqrt(lengthSquaredv1)
	                         * Math.sqrt(lengthSquaredv2);
	    
	    // correct for floating-point rounding errors
	    if (denominator < dotProduct) {
	      denominator = dotProduct;
	    }
	    
	    double distance = 1.0 - dotProduct / denominator;
	    
	    if (distance < 0.5) {
	      return (1 - distance) * (distance * distance) + distance
	             * Math.sqrt(distance);
	    } else return Math.sqrt(distance);
	  }
	  
	  @Override
	  public double distance(double centroidLengthSquare,
	                         Vector centroid,
	                         Vector v) {
	    return distance(centroid, v);
	  }
	    
	  @Override
	  public Collection<Parameter<?>> getParameters() {
	    return Collections.emptyList();
	  }

	  @Override
	  public void createParameters(String prefix, Configuration jobConf) {
	    // TODO Auto-generated method stub
	    
	  }

	  @Override
	  public void configure(Configuration config) {
	    // TODO Auto-generated method stub
	    
	  }
}
</span></strong>