Marker of metric properties backported from MESSIF v3.

/*

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package messif.distance;

/**

 * This is a marking interface (no methods) saying that a distance fulfills all metric postulates.

 * @author David Novak, Masaryk University, Brno, Czech Republic, david.novak@fi.muni.cz

 */

public interface Metric extends Reflexive, Symmetric, Triangle {

}

/*

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package messif.distance;

/**

 * This is a marking interface (no methods) saying that a distance fulfills the reflexivity condition.

 * @author David Novak, Masaryk University, Brno, Czech Republic, david.novak@fi.muni.cz

 */

public interface Reflexive {

}

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package messif.distance;

/**

 * This is a marking interface (no methods) saying that a distance fulfills the symmetry.

 * @author David Novak, Masaryk University, Brno, Czech Republic, david.novak@fi.muni.cz

 */

public interface Symmetric {

}

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package messif.distance;

/**

 * This is a marking interface (no methods) saying that a distance fulfills the triangle inequality.

 * @author David Novak, Masaryk University, Brno, Czech Republic, david.novak@fi.muni.cz

 */

public interface Triangle {

}

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package messif.objects.impl;

import java.io.BufferedReader;

import java.io.EOFException;

import java.io.IOException;

import messif.distance.Metric;

import messif.objects.LocalAbstractObject;

import messif.objects.nio.BinaryInput;

import messif.objects.nio.BinarySerializator;

/**

 * Implementation of the {@link ObjectFloatVector} with a Angular <b>metric</b> distance.

 *

 * @author Vlastislav Dohnal, Masaryk University, Brno, Czech Republic, dohnal@fi.muni.cz

 */

public class ObjectFloatVectorAngular extends ObjectFloatVector implements Metric {

    // class id for serialization

    private static final long serialVersionUID = 1L;

    //****************** Constructors ******************//

    /**

     * Creates a new instance of {@link ObjectFloatVectorAngular}.

     *

     * @param data the data content of the new object

     */

    public ObjectFloatVectorAngular(float[] data) {

        super(data);

    }

    /**

     * Creates a new instance of {@link ObjectFloatVectorAngular} with randomly

     * generated content data. Content will be generated using normal

     * distribution of random numbers from interval [min;max).

     *

     * @param dimension number of dimensions to generate

     * @param min lower bound of the random generated values (inclusive)

     * @param max upper bound of the random generated values (exclusive)

     */

    public ObjectFloatVectorAngular(int dimension, float min, float max) {

        super(dimension, min, max);

    }

    /**

     * Creates a new instance of {@link ObjectFloatVectorAngular} from text

     * stream.

     *

     * @param stream the stream from which to read lines of text

     * @throws EOFException if the end-of-file of the given stream is reached

     * @throws IOException if there was an I/O error during reading from the

     * stream

     * @throws NumberFormatException if a line read from the stream does not

     * consist of comma-separated or space-separated numbers

     */

    public ObjectFloatVectorAngular(BufferedReader stream) throws EOFException, IOException, NumberFormatException {

        super(stream);

    }

    //****************** Distance function ******************//

    /**

     * Calculates the Angular distance which is a metric.

     * @param obj object to measure the similarity from

     * @param distThreshold distance threshold (not used)

     * @return the "angular" distance between two vectors (angle they enclose)

     */

    @Override

    protected float getDistanceImpl(LocalAbstractObject obj, float distThreshold) {

        float[] objData = ((ObjectFloatVector) obj).data;

        if (objData.length != data.length) {

            throw new IllegalArgumentException("Cannot compute distance on different vector dimensions (" + data.length + ", " + objData.length + ")");

        }

        double productSum = 0f;

        double powASum = 0f;

        double powBSum = 0f;

        for (int i = 0; i < data.length; i++) {

            productSum += data[i] * objData[i];

            powASum += data[i] * data[i];

            powBSum += objData[i] * objData[i];

        }

        float cosineDist = 1f - (float) (Math.abs(productSum) / Math.sqrt(powASum) * Math.sqrt(powBSum));

        return (float)Math.acos(cosineDist);        // possibly normalized it by Math.PI

    }

    //************ BinarySerializable interface ************//

    /**

     * Creates a new instance of {@link ObjectFloatVectorAngular} loaded from

     * binary input buffer.

     *

     * @param input the buffer to read the ObjectFloatVector from

     * @param serializator the serializator used to write objects

     * @throws IOException if there was an I/O error reading from the buffer

     */

    protected ObjectFloatVectorAngular(BinaryInput input, BinarySerializator serializator) throws IOException {

        super(input, serializator);

    }

}