kernel.c

支持向量机作为统计学习理论的实现方法

/* --------------------------------------------------------------------
 Provides a function for evaluation of kernel function. This function 
 is used in smo.c, svmclass2.c,etc.

 Statistical Pattern Recognition Toolbox, Vojtech Franc, Vaclav Hlavac
 (c) Czech Technical University Prague, http://cmp.felk.cvut.cz

 Modifications:
 12-November-2001, V.Franc, sigmoid kenel
 22-September-2001, V. Franc, created.
-------------------------------------------------------------------- */

#include "mex.h"
#include "matrix.h"
#include <math.h>

/* --- Global variables --------------------------------------------- */

double *dataA;      /* pointer at the fist patterns */
double *dataB;      /* pointer at the second patterns */
long dim;           /* dimension of patterns */
int ker;            /* kernel type (0 - linear, 1 - polynom, 
                       2 - rbf, 3 - sigmoid */
double arg1;        /* 1st argument of the kernel */
double arg2;        /* 2nd argument --//-- */
long ker_cnt;       /* number of cernel evaluations */


/* -------------------------------------------------------------------
 Computes dot product of a-th and b-th vector.
 c = a'*b
------------------------------------------------------------------- */
double dot_prod( long a, long b)
{
   double c = 0;
   long i;
   for( i = 0; i < dim; i++ ) {
      c += *(dataA+(a*dim)+i) * *(dataB+(b*dim)+i);
   }
   return( c );
}

/* -------------------------------------------------------------------
 Computes dot product of subtraction of a-th and b-th vector.
 c = (a-b)'*(a-b)
------------------------------------------------------------------- */
double sub_dot_prod( long a, long b )
{
   double c = 0;
   long i;
   for( i = 0; i < dim; i++ ) {
      c += (*(dataA+(a*dim)+i) - *(dataB+(b*dim)+i))*
           (*(dataA+(a*dim)+i) - *(dataB+(b*dim)+i));
   }
   return( c );
}

/* --------------------------------------------------------------------
 Computes kernel function for a-th and b-th.

 The base address for the 1st argument is dataA and for the 2nd
 argument is dataB.
-------------------------------------------------------------------- */
double kernel( long a, long b )
{
   double c = 0;

   ker_cnt++;

   switch( ker ) {
      /* polynomial kernel */
      case 1:
         c = pow( (dot_prod( a, b) + 1), arg1 );
         break;
      /* radial basis functions kernel*/
      case 2:
         c = exp( sub_dot_prod( a, b)/arg1 );
         break;
      /* sigmoid */
      case 3:     
         c = tanh( arg1*dot_prod( a,b) + arg2 );
         break;
      /* linear kernel */
      default:
         c = dot_prod( a, b );
   }
   return( c );
}