GaussianMatchStringKernel.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) 1999-2009 Soeren Sonnenburg
 * Copyright (C) 1999-2009 Fraunhofer Institute FIRST and Max-Planck-Society
 */

#include "lib/common.h"
#include "lib/io.h"
#include "kernel/GaussianMatchStringKernel.h"
#include "kernel/SqrtDiagKernelNormalizer.h"
#include "features/Features.h"
#include "features/StringFeatures.h"

using namespace shogun;

CGaussianMatchStringKernel::CGaussianMatchStringKernel(int32_t size, float64_t w)
: CStringKernel<char>(size), width(w)
{
    set_normalizer(new CSqrtDiagKernelNormalizer());
}

CGaussianMatchStringKernel::CGaussianMatchStringKernel(
    CStringFeatures<char>* l, CStringFeatures<char>* r, float64_t w)
: CStringKernel<char>(10), width(w)
{
    set_normalizer(new CSqrtDiagKernelNormalizer());
    init(l, r);
}

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

bool CGaussianMatchStringKernel::init(CFeatures* l, CFeatures* r)
{
    CStringKernel<char>::init(l, r);
    return init_normalizer();
}

void CGaussianMatchStringKernel::cleanup()
{
    CKernel::cleanup();
}

float64_t CGaussianMatchStringKernel::compute(int32_t idx_a, int32_t idx_b)
{
    int32_t i, alen, blen ;
    bool free_avec, free_bvec;

    char* avec = ((CStringFeatures<char>*) lhs)->get_feature_vector(idx_a, alen, free_avec);
    char* bvec = ((CStringFeatures<char>*) rhs)->get_feature_vector(idx_b, blen, free_bvec);

    float64_t result=0;

    ASSERT(alen==blen);

    for (i = 0;  i<alen; i++) 
        result+=(avec[i]==bvec[i]) ? 0:4;

    result=exp(-result/width);


    ((CStringFeatures<char>*) lhs)->free_feature_vector(avec, idx_a, free_avec);
    ((CStringFeatures<char>*) rhs)->free_feature_vector(bvec, idx_b, free_bvec);
    return result;
}