/usr/include/shogun/kernel/GaussianKernel.h is in libshogun-dev 1.1.0-4ubuntu2.
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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) 1999-2010 Soeren Sonnenburg
* Written (W) 2011 Abhinav Maurya
* Copyright (C) 1999-2009 Fraunhofer Institute FIRST and Max-Planck-Society
* Copyright (C) 2010 Berlin Institute of Technology
*/
#ifndef _GAUSSIANKERNEL_H___
#define _GAUSSIANKERNEL_H___
#include <shogun/lib/common.h>
#include <shogun/kernel/Kernel.h>
#include <shogun/kernel/DotKernel.h>
#include <shogun/features/DotFeatures.h>
namespace shogun
{
class CDotFeatures;
/** @brief The well known Gaussian kernel (swiss army knife for SVMs)
* computed on CDotFeatures.
*
* It is computed as
*
* \f[
* k({\bf x},{\bf x'})= exp(-\frac{||{\bf x}-{\bf x'}||^2}{\tau})
* \f]
*
* where \f$\tau\f$ is the kernel width.
*
* The compact version as given in Bart Hamers' thesis <i>Kernel Models for Large Scale Applications</i> (Eq. 4.10) is computed as
*
* \f[
* k({\bf x},{\bf x'})= max(0, (1-\frac{||{\bf x}-{\bf x'}||}{3\tau})^v)) * exp(-\frac{||{\bf x}-{\bf x'}||^2}{\tau})
* \f]
*
* where \f$\tau\f$ is the kernel width.
*
*/
class CGaussianKernel: public CDotKernel
{
public:
/** default constructor
*
*/
CGaussianKernel();
/** constructor
*
* @param size cache size
* @param width width
*/
CGaussianKernel(int32_t size, float64_t width);
/** constructor
*
* @param l features of left-hand side
* @param r features of right-hand side
* @param width width
* @param size cache size
*/
CGaussianKernel(CDotFeatures* l, CDotFeatures* r,
float64_t width, int32_t size=10);
virtual ~CGaussianKernel();
/** initialize kernel
*
* @param l features of left-hand side
* @param r features of right-hand side
* @return if initializing was successful
*/
virtual bool init(CFeatures* l, CFeatures* r);
/** clean up kernel */
virtual void cleanup();
/** return what type of kernel we are
*
* @return kernel type GAUSSIAN
*/
virtual EKernelType get_kernel_type() { return K_GAUSSIAN; }
/** return the kernel's name
*
* @return name Gaussian
*/
inline virtual const char* get_name() const { return "GaussianKernel"; }
/** set the kernel's width
*
* @param w kernel width
*/
inline virtual void set_width(float64_t w)
{
width=w;
}
/** return the kernel's width
*
* @return kernel width
*/
inline virtual float64_t get_width() const
{
return width;
}
/** set the compact option
*
* @param compact value of the compact option
*/
inline void set_compact_enabled(bool compact)
{
m_compact = compact;
}
/** return value of the compact option
*
* @return whether the compact option is enabled
*/
inline bool get_compact_enabled()
{
return m_compact;
}
protected:
/** compute kernel function for features a and b
* idx_{a,b} denote the index of the feature vectors
* in the corresponding feature object
*
* @param idx_a index a
* @param idx_b index b
* @return computed kernel function at indices a,b
*/
virtual float64_t compute(int32_t idx_a, int32_t idx_b);
/** Can (optionally) be overridden to post-initialize some
* member variables which are not PARAMETER::ADD'ed. Make
* sure that at first the overridden method
* BASE_CLASS::LOAD_SERIALIZABLE_POST is called.
*
* @exception ShogunException Will be thrown if an error
* occurres.
*/
virtual void load_serializable_post() throw (ShogunException);
private:
/** helper function to compute quadratic terms in
* (a-b)^2 (== a^2+b^2-2ab)
*/
void precompute_squared();
/** helper function to compute quadratic terms in
* (a-b)^2 (== a^2+b^2-2ab)
*
* @param buf buffer to store squared terms (will be allocated)
* @param df dot feature object based on which k(i,i) is computed
* */
void precompute_squared_helper(float64_t* &buf, CDotFeatures* df);
void init();
protected:
/** width */
float64_t width;
/** squared left-hand side */
float64_t* sq_lhs;
/** squared right-hand side */
float64_t* sq_rhs;
/** whether compact output enabled */
bool m_compact;
};
}
#endif /* _GAUSSIANKERNEL_H__ */
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