net.sourceforge.cilib.util.distancemeasure.MinkowskiMetric Maven / Gradle / Ivy
/** __ __
* _____ _/ /_/ /_ Computational Intelligence Library (CIlib)
* / ___/ / / / __ \ (c) CIRG @ UP
* / /__/ / / / /_/ / http://cilib.net
* \___/_/_/_/_.___/
*/
package net.sourceforge.cilib.util.distancemeasure;
import java.util.Collection;
import java.util.Iterator;
import net.sourceforge.cilib.type.types.Numeric;
/**
* The Minkowski Metric is a generic measure of distance. It is defined in:
*
* Article{ 331504, author = "A. K. Jain and M. N. Murty and P. J. Flynn", title = "Data
* Clustering: A Review", journal = "ACM Computing Surveys", volume = "31", number = "3",
* year = "1999", issn = "0360-0300", pages = "264--323", doi =
* "http://0-doi.acm.org.innopac.up.ac.za:80/10.1145/331499.331504", publisher = "ACM
* Press", address = "New York, NY, USA" }
*
* {@link ManhattanDistanceMeasure} is a special case of the Minkowski Metric with 'alpha' := 1.
* {@link EuclideanDistanceMeasure} is a special case of the Minkowski Metric with 'alpha' := 2.
*
* NOTE: The default 'alpha' value is 0 when this class is instantiated.
*/
public class MinkowskiMetric implements DistanceMeasure {
protected int alpha = 0;
/**
* Instantiate the Minkowski Metric with 'alpha' value equal to zero. This means
* that you have to call the setAlpha method right after calling this constructor.
*/
public MinkowskiMetric() {
alpha = 0;
}
/**
* Instantiate the Minkowski Metric with the specified 'alpha' value.
* @param a the value to which 'alpha' should be set
*/
public MinkowskiMetric(int a) {
if (a < 1) {
throw new IllegalArgumentException("The 'alpha' parameter of the Minkowski Metric must be >= 1");
}
alpha = a;
}
/**
* Calculate the distance between two vectors.
* @param x the first vector.
* @param y the second vector.
* @return the distance (as a double) between the two vectors.
* @throws IllegalArgumentException when the two vectors' dimension differ.
*/
public double distance(Collection x, Collection y) {
if (x.size() != y.size()) {
throw new IllegalArgumentException("Cannot calculate Minkowski Metric for vectors of different dimensions: " + x.size() + " != " + y.size());
}
if (alpha < 1) {
throw new IllegalArgumentException("The 'alpha' parameter of the Minkowski Metric must be >= 1, i.e. not " + alpha);
}
Iterator xIterator = x.iterator();
Iterator yIterator = y.iterator();
double distance = 0.0;
for (int i = 0; i < x.size(); ++i) {
Numeric xElement = (Numeric) xIterator.next();
Numeric yElement = (Numeric) yIterator.next();
distance += Math.pow(Math.abs(xElement.doubleValue() - yElement.doubleValue()), alpha);
}
return Math.pow(distance, 1.0 / alpha);
}
/**
* Set the 'alpha' value that will be used in the calculation of the Minkowski Metric.
* @param a the new 'alpha' value
* @throws IllegalArgumentException when the given parameter is less than one.
*/
public void setAlpha(int a) {
if (a < 1) {
throw new IllegalArgumentException("The 'alpha' parameter of the Minkowski Metric must be >= 1");
}
alpha = a;
}
}