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SqrtDiagKernelNormalizer.h
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SqrtDiagKernelNormalizer.h
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/*
* This software is distributed under BSD 3-clause license (see LICENSE file).
*
* Authors: Soeren Sonnenburg, Yuyu Zhang, Sergey Lisitsyn
*/
#ifndef _SQRTDIAGKERNELNORMALIZER_H___
#define _SQRTDIAGKERNELNORMALIZER_H___
#include <shogun/lib/config.h>
#include <shogun/kernel/normalizer/KernelNormalizer.h>
#include <shogun/kernel/string/CommWordStringKernel.h>
namespace shogun
{
/** @brief SqrtDiagKernelNormalizer divides by the Square Root of the product of
* the diagonal elements.
*
* This effectively normalizes the vectors in feature space to norm 1 (see
* CSqrtDiagKernelNormalizer)
*
* \f[
* k'({\bf x},{\bf x'}) = \frac{k({\bf x},{\bf x'})}{\sqrt{k({\bf x},{\bf x})k({\bf x'},{\bf x'})}}
* \f]
*/
class CSqrtDiagKernelNormalizer : public CKernelNormalizer
{
public:
/** default constructor
* @param use_opt_diag - some kernels support faster diagonal compuation
* via compute_diag(idx), this flag enables this
*/
CSqrtDiagKernelNormalizer(bool use_opt_diag=false): CKernelNormalizer(),
sqrtdiag_lhs(NULL), num_sqrtdiag_lhs(0),
sqrtdiag_rhs(NULL), num_sqrtdiag_rhs(0),
use_optimized_diagonal_computation(use_opt_diag)
{
m_parameters->add_vector(&sqrtdiag_lhs, &num_sqrtdiag_lhs, "sqrtdiag_lhs",
"sqrt(K(x,x)) for left hand side examples.");
watch_param("sqrtdiag_lhs", &sqrtdiag_lhs, &num_sqrtdiag_lhs);
m_parameters->add_vector(&sqrtdiag_rhs, &num_sqrtdiag_rhs, "sqrtdiag_rhs",
"sqrt(K(x,x)) for right hand side examples.");
watch_param("sqrtdiag_rhs", &sqrtdiag_rhs, &num_sqrtdiag_rhs);
SG_ADD(&use_optimized_diagonal_computation,
"use_optimized_diagonal_computation",
"flat if optimized diagonal computation is used", MS_NOT_AVAILABLE);
}
/** default destructor */
virtual ~CSqrtDiagKernelNormalizer()
{
SG_FREE(sqrtdiag_lhs);
SG_FREE(sqrtdiag_rhs);
}
/** initialization of the normalizer
* @param k kernel */
virtual bool init(CKernel* k)
{
ASSERT(k)
num_sqrtdiag_lhs=k->get_num_vec_lhs();
num_sqrtdiag_rhs=k->get_num_vec_rhs();
ASSERT(num_sqrtdiag_lhs>0)
ASSERT(num_sqrtdiag_rhs>0)
CFeatures* old_lhs=k->lhs;
CFeatures* old_rhs=k->rhs;
k->lhs=old_lhs;
k->rhs=old_lhs;
bool r1=alloc_and_compute_diag(k, sqrtdiag_lhs, num_sqrtdiag_lhs);
k->lhs=old_rhs;
k->rhs=old_rhs;
bool r2=alloc_and_compute_diag(k, sqrtdiag_rhs, num_sqrtdiag_rhs);
k->lhs=old_lhs;
k->rhs=old_rhs;
return r1 && r2;
}
/** normalize the kernel value
* @param value kernel value
* @param idx_lhs index of left hand side vector
* @param idx_rhs index of right hand side vector
*/
virtual float64_t normalize(
float64_t value, int32_t idx_lhs, int32_t idx_rhs)
{
float64_t sqrt_both=sqrtdiag_lhs[idx_lhs]*sqrtdiag_rhs[idx_rhs];
return value/sqrt_both;
}
/** normalize only the left hand side vector
* @param value value of a component of the left hand side feature vector
* @param idx_lhs index of left hand side vector
*/
virtual float64_t normalize_lhs(float64_t value, int32_t idx_lhs)
{
return value/sqrtdiag_lhs[idx_lhs];
}
/** normalize only the right hand side vector
* @param value value of a component of the right hand side feature vector
* @param idx_rhs index of right hand side vector
*/
virtual float64_t normalize_rhs(float64_t value, int32_t idx_rhs)
{
return value/sqrtdiag_rhs[idx_rhs];
}
public:
/**
* alloc and compute the vector containing the square root of the
* diagonal elements of this kernel.
*/
bool alloc_and_compute_diag(CKernel* k, float64_t* &v, int32_t num)
{
SG_FREE(v);
v=SG_MALLOC(float64_t, num);
for (int32_t i=0; i<num; i++)
{
if (k->get_kernel_type() == K_COMMWORDSTRING)
{
if (use_optimized_diagonal_computation)
v[i]=sqrt(((CCommWordStringKernel*) k)->compute_diag(i));
else
v[i]=sqrt(((CCommWordStringKernel*) k)->compute_helper(i,i, true));
}
else
v[i]=sqrt(k->compute(i,i));
if (v[i]==0.0)
v[i]=1e-16; /* avoid divide by zero exception */
}
return (v!=NULL);
}
/** @return object name */
virtual const char* get_name() const { return "SqrtDiagKernelNormalizer"; }
protected:
/** sqrt diagonal left-hand side */
float64_t* sqrtdiag_lhs;
/** num sqrt diagonal left-hand side */
int32_t num_sqrtdiag_lhs;
/** sqrt diagonal right-hand side */
float64_t* sqrtdiag_rhs;
/** num sqrt diagonal right-hand side */
int32_t num_sqrtdiag_rhs;
/** f optimized diagonal computation is used */
bool use_optimized_diagonal_computation;
};
}
#endif