/**
* Licensed to the Apache Software Foundation (ASF) under one or more
* contributor license agreements. See the NOTICE file distributed with
* this work for additional information regarding copyright ownership.
* The ASF licenses this file to You under the Apache License, Version 2.0
* (the "License"); you may not use this file except in compliance with
* the License. You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package org.apache.mahout.common.distance;
import java.util.ArrayList;
import java.util.Collection;
import java.util.Iterator;
import java.util.List;
import org.apache.hadoop.conf.Configuration;
import org.apache.mahout.common.parameters.DoubleParameter;
import org.apache.mahout.common.parameters.Parameter;
import org.apache.mahout.math.Vector;
import org.apache.mahout.math.Vector.Element;
/**
* Implement Minkowski distance, a real-valued generalization of the
* integral L(n) distances: Manhattan = L1, Euclidean = L2.
* For high numbers of dimensions, very high exponents give more useful distances.
*
* Note: Math.pow is clever about integer-valued doubles.
**/
public class MinkowskiDistanceMeasure implements DistanceMeasure {
private static final double EXPONENT = 3.0;
private List<Parameter<?>> parameters;
private double exponent = EXPONENT;
public MinkowskiDistanceMeasure() {
}
public MinkowskiDistanceMeasure(double exponent) {
this.exponent = exponent;
}
@Override
public void createParameters(String prefix, Configuration conf) {
parameters = new ArrayList<Parameter<?>>();
Parameter<?> param =
new DoubleParameter(prefix, "exponent", conf, EXPONENT, "Exponent for Fractional Lagrange distance");
parameters.add(param);
}
@Override
public Collection<Parameter<?>> getParameters() {
return parameters;
}
@Override
public void configure(Configuration jobConf) {
if (parameters == null) {
ParameteredGeneralizations.configureParameters(this, jobConf);
}
}
public double getExponent() {
return exponent;
}
public void setExponent(double exponent) {
this.exponent = exponent;
}
/**
* Math.pow is clever about integer-valued doubles
*/
@Override
public double distance(Vector v1, Vector v2) {
Vector distVector = v1.minus(v2);
double sum = 0.0;
Iterator<Element> it = distVector.iterateNonZero();
while (it.hasNext()) {
Element e = it.next();
sum += Math.pow(Math.abs(e.get()), exponent);
}
return Math.pow(sum, 1.0 / exponent);
}
// TODO: how?
@Override
public double distance(double centroidLengthSquare, Vector centroid, Vector v) {
return distance(centroid, v); // TODO - can this use centroidLengthSquare somehow?
}
}