GaussianShiftKernel.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) 2008 Gunnar Raetsch
 * Copyright (C) 2008-2009 Fraunhofer Institute FIRST and Max-Planck-Society
 */

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

using namespace shogun;

CGaussianShiftKernel::CGaussianShiftKernel()
: CGaussianKernel(), max_shift(0), shift_step(0)
{
    init();
}

CGaussianShiftKernel::CGaussianShiftKernel(
    int32_t size, float64_t w, int32_t ms, int32_t ss)
: CGaussianKernel(size, w), max_shift(ms), shift_step(ss)
{
    init();
}

CGaussianShiftKernel::CGaussianShiftKernel(
    CDenseFeatures<float64_t>* l, CDenseFeatures<float64_t>* r, float64_t w, int32_t ms, int32_t ss,
    int32_t size)
: CGaussianKernel(l, r, w, size), max_shift(ms), shift_step(ss)
{
    init();
    init(l,r);
}

CGaussianShiftKernel::~CGaussianShiftKernel()
{
}

float64_t CGaussianShiftKernel::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 = 0.0 ;
    float64_t sum=0.0 ;
    for (int32_t i=0; i<alen; i++)
        sum+=(avec[i]-bvec[i])*(avec[i]-bvec[i]);
    result += exp(-sum/get_width()) ;

    for (int32_t shift = shift_step, s=1; shift<max_shift; shift+=shift_step, s++)
    {
        sum=0.0 ;
        for (int32_t i=0; i<alen-shift; i++)
            sum+=(avec[i+shift]-bvec[i])*(avec[i+shift]-bvec[i]);
        result += exp(-sum/get_width())/(2*s) ;

        sum=0.0 ;
        for (int32_t i=0; i<alen-shift; i++)
            sum+=(avec[i]-bvec[i+shift])*(avec[i]-bvec[i+shift]);
        result += exp(-sum/get_width())/(2*s) ;
    }

    ((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 CGaussianShiftKernel::init()
{
    SG_ADD(&max_shift, "max_shift", "Maximum shift.", MS_AVAILABLE);
    SG_ADD(&shift_step, "shift_step", "Shift stepsize.", MS_AVAILABLE);
}