SphericalKernel.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.
 *
 * Based on GaussianKernel, Written (W) 1999-2010 Soeren Sonnenburg
 * Written (W) 2011 Shashwat Lal Das
 * Copyright (C) 2011 Berlin Institute of Technology and Max-Planck-Society
 */

#include <shogun/kernel/SphericalKernel.h>
#include <shogun/mathematics/Math.h>

using namespace shogun;

CSphericalKernel::CSphericalKernel(): CKernel(0), distance(NULL)
{
    init();
    set_sigma(1.0);
}

CSphericalKernel::CSphericalKernel(int32_t size, float64_t sig, CDistance* dist)
: CKernel(size), distance(dist)
{
    ASSERT(distance);
    SG_REF(distance);
    init();
    set_sigma(sig);
}

CSphericalKernel::CSphericalKernel(
    CFeatures *l, CFeatures *r, float64_t sig, CDistance* dist)
: CKernel(10), distance(dist)
{
    ASSERT(distance);
    SG_REF(distance);
    init();
    set_sigma(sig);
    init(l, r);
}

CSphericalKernel::~CSphericalKernel()
{
    cleanup();
    SG_UNREF(distance);
}

bool CSphericalKernel::init(CFeatures* l, CFeatures* r)
{
    ASSERT(distance);
    CKernel::init(l,r);
    distance->init(l,r);
    return init_normalizer();
}

void CSphericalKernel::init()
{
    m_parameters->add((CSGObject**) &distance, "distance", "Distance to be used.");
    m_parameters->add(&sigma, "sigma", "Sigma kernel parameter.");
}

float64_t CSphericalKernel::compute(int32_t idx_a, int32_t idx_b)
{
    float64_t dist=distance->distance(idx_a, idx_b);
    float64_t ds_ratio=dist/sigma;

    if (dist < sigma) 
        return 1.0-1.5*(ds_ratio)+0.5*(ds_ratio*ds_ratio*ds_ratio);
    else
        return 0;
}