org.apache.mahout.common.distance.SquaredEuclideanDistanceMeasure.java Source code

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Here is the source code for org.apache.mahout.common.distance.SquaredEuclideanDistanceMeasure.java

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/**
 * 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.Collection;
import java.util.Collections;

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

/**
 * 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(Configuration job) {
        // nothing to do
    }

    @Override
    public Collection<Parameter<?>> getParameters() {
        return Collections.emptyList();
    }

    @Override
    public void createParameters(String prefix, Configuration jobConf) {
        // nothing to do
    }

    @Override
    public double distance(Vector v1, Vector v2) {
        return v2.getDistanceSquared(v1);
    }

    @Override
    public double distance(double centroidLengthSquare, Vector centroid, Vector v) {
        return centroidLengthSquare - 2 * v.dot(centroid) + v.getLengthSquared();
    }
}