/**
* 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 org.apache.hadoop.mapred.JobConf;
import org.apache.mahout.matrix.CardinalityException;
import org.apache.mahout.matrix.Vector;
import org.apache.mahout.common.parameters.Parameter;
import java.util.Collection;
import java.util.Collections;
/**
* Like {@link EuclideanDistanceMeasure} but it does not take the square root. <p/> Thus, it is
* not actually the Euclidean Distance, but it is saves on computation when you only need the distance for comparison
* and don't care about the actual value as a distance.
*/
public class SquaredEuclideanDistanceMeasure implements DistanceMeasure {
@Override
public void configure(JobConf job) {
// nothing to do
}
@Override
public Collection<Parameter<?>> getParameters() {
return Collections.emptyList();
}
@Override
public void createParameters(String prefix, JobConf jobConf) {
// nothing to do
}
@Override
public double distance(Vector v1, Vector v2) {
if (v1.size() != v2.size()) {
throw new CardinalityException();
}
Vector vector = v1.minus(v2);
return vector.dot(vector);
}
@Override
public double distance(double centroidLengthSquare, Vector centroid, Vector v) {
if (centroid.size() != v.size()) {
throw new CardinalityException();
}
return centroidLengthSquare + v.getDistanceSquared(centroid);
}
}