GeodesicMetric.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) 2006-2009 Christian Gehl
 * Copyright (C) 2006-2009 Fraunhofer Institute FIRST
 */

#include <shogun/lib/config.h>
#include <shogun/lib/common.h>
#include <shogun/io/SGIO.h>
#include <shogun/distance/GeodesicMetric.h>
#include <shogun/features/Features.h>

using namespace shogun;

CGeodesicMetric::CGeodesicMetric() : CDenseDistance<float64_t>()
{
}

CGeodesicMetric::CGeodesicMetric(CDenseFeatures<float64_t>* l, CDenseFeatures<float64_t>* r)
: CDenseDistance<float64_t>()
{
    init(l, r);
}

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

bool CGeodesicMetric::init(CFeatures* l, CFeatures* r)
{
    bool result=CDenseDistance<float64_t>::init(l,r);

    return result;
}

void CGeodesicMetric::cleanup()
{
}

float64_t CGeodesicMetric::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 s=0;
    float64_t d=0;
    float64_t nx=0;
    float64_t ny=0;
    {
        for (int32_t i=0; i<alen; i++)
        {
            d+=avec[i]*bvec[i];
            nx+=avec[i]*avec[i];
            ny+=bvec[i]*bvec[i];
            s+=avec[i]+bvec[i];
        }
    }

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


    // trap division by zero
    if(s==0 || nx==0 || ny==0)
        return 0;

    d/=CMath::sqrt(nx*ny);

    // can only happen due to numerical problems
    if (CMath::abs(d)>1.0)
        d=CMath::sign(d);

    return acos(d);
}