JensenShannonKernel.cpp

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/*
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation; either version 3 of the License, or
 * (at your option) any later version.
 *
 * Written (W) 2012 Viktor Gal
 * Copyright (C) 2012 Viktor Gal
 */

#include <shogun/lib/common.h>
#include <shogun/kernel/JensenShannonKernel.h>
#include <shogun/features/Features.h>
#include <shogun/io/SGIO.h>

using namespace shogun;

CJensenShannonKernel::CJensenShannonKernel()
: CDotKernel(0)
{
}

CJensenShannonKernel::CJensenShannonKernel(int32_t size)
: CDotKernel(size)
{
}

CJensenShannonKernel::CJensenShannonKernel(
    CDenseFeatures<float64_t>* l, CDenseFeatures<float64_t>* r, int32_t size)
: CDotKernel(size)
{
    init(l,r);
}

CJensenShannonKernel::~CJensenShannonKernel()
{
    cleanup();
}

bool CJensenShannonKernel::init(CFeatures* l, CFeatures* r)
{
    bool result=CDotKernel::init(l,r);
    init_normalizer();
    return result;
}

float64_t CJensenShannonKernel::compute(int32_t idx_a, int32_t idx_b)
{
    int32_t alen, blen;
    bool afree, bfree;

    float64_t* avec=
        ((CDenseFeatures<float64_t>*) lhs)->get_feature_vector(idx_a, alen, afree);
    float64_t* bvec=
        ((CDenseFeatures<float64_t>*) rhs)->get_feature_vector(idx_b, blen, bfree);
    ASSERT(alen==blen)

    float64_t result=0;

    /* calcualte Jensen-Shannon kernel */
    for (int32_t i=0; i<alen; i++) {
        float64_t a_i = 0, b_i = 0;
        float64_t ab = avec[i]+bvec[i];
        if (avec[i] != 0)
            a_i = avec[i] * CMath::log2(ab/avec[i]);
        if (bvec[i] != 0)
            b_i = bvec[i] * CMath::log2(ab/bvec[i]);

        result += 0.5*(a_i + b_i);
    }

    ((CDenseFeatures<float64_t>*) lhs)->free_feature_vector(avec, idx_a, afree);
    ((CDenseFeatures<float64_t>*) rhs)->free_feature_vector(bvec, idx_b, bfree);

    return result;
}