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CosineDist.java

/*
 *  Copyright 2006-2007 Columbia University.
 *
 *  This file is part of MEAPsoft.
 *
 *  MEAPsoft is free software; you can redistribute it and/or modify
 *  it under the terms of the GNU General Public License version 2 as
 *  published by the Free Software Foundation.
 *
 *  MEAPsoft is distributed in the hope that it will be useful, but
 *  WITHOUT ANY WARRANTY; without even the implied warranty of
 *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
 *  General Public License for more details.
 *
 *  You should have received a copy of the GNU General Public License
 *  along with MEAPsoft; if not, write to the Free Software
 *  Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA
 *  02110-1301 USA
 *
 *  See the file "COPYING" for the text of the license.
 */

package com.meapsoft;

public class CosineDist extends ChunkDist 
{
    public CosineDist() {}
    public CosineDist(ChunkDist o) { super(o); }
    public CosineDist(int[] i) { super(i); }
    public CosineDist(ChunkDist o, int[] i) { super(o,i); }

    public double distance(Chunk ch1, Chunk ch2) 
    {
        FeatChunk c1 = null;
        FeatChunk c2 = null; 

        // this only works on FeatChunks
        try
        {
            c1 = (FeatChunk)ch1;
            c2 = (FeatChunk)ch2;
        }
        catch(ClassCastException e)
        {
            return super.distance(ch1, ch2);
        }

        double[] f1 = c1.getFeatures(featdim);
        double[] f2 = c2.getFeatures(featdim);
        double dist = 0;
        double normf1 = 0;
        double normf2 = 0;

        for(int i = 0; i < f1.length; i++)
        {
            dist += f1[i]*f2[i];
            normf1 +=  f1[i]*f1[i];
            normf2 +=  f2[i]*f2[i];
        }
        
        dist = super.distance(ch1, ch2) + 1 - dist/Math.sqrt(normf1*normf2);

        return dist;
    }
}

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