HistogramIntersectionKernel.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) 2010 Koen van de Sande
 * Copyright (C) 2010 Koen van de Sande / University of Amsterdam
 */

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

using namespace shogun;

CHistogramIntersectionKernel::CHistogramIntersectionKernel()
: CDotKernel(0), m_beta(1.0)
{
    register_params();
}

CHistogramIntersectionKernel::CHistogramIntersectionKernel(int32_t size)
: CDotKernel(size), m_beta(1.0)
{
    register_params();
}

CHistogramIntersectionKernel::CHistogramIntersectionKernel(
    CDenseFeatures<float64_t>* l, CDenseFeatures<float64_t>* r,
    float64_t beta, int32_t size)
: CDotKernel(size), m_beta(beta)
{
    init(l,r);
    register_params();
}

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

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

float64_t CHistogramIntersectionKernel::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;

    // checking if beta is default or not
    if (m_beta == 1.0)
    {
        // compute standard histogram intersection kernel
        for (int32_t i=0; i<alen; i++)
            result += (avec[i] < bvec[i]) ? avec[i] : bvec[i];
    }
    else
    {
        //compute generalized histogram intersection kernel
        for (int32_t i=0; i<alen; i++)
            result += CMath::min(CMath::pow(avec[i],m_beta), CMath::pow(bvec[i],m_beta));
    }
    ((CDenseFeatures<float64_t>*) lhs)->free_feature_vector(avec, idx_a, afree);
    ((CDenseFeatures<float64_t>*) rhs)->free_feature_vector(bvec, idx_b, bfree);

    return result;
}

void CHistogramIntersectionKernel::register_params()
{
    SG_ADD(&m_beta, "beta", "the beta parameter of the kernel", MS_AVAILABLE);
}