Daniel@0: /************************************************************************/
Daniel@0: /*                                                                      */
Daniel@0: /*   kernel.h                                                           */
Daniel@0: /*                                                                      */
Daniel@0: /*   User defined kernel function. Feel free to plug in your own.       */
Daniel@0: /*                                                                      */
Daniel@0: /*   Copyright: Thorsten Joachims                                       */
Daniel@0: /*   Date: 16.12.97                                                     */
Daniel@0: /*                                                                      */
Daniel@0: /************************************************************************/
Daniel@0: 
Daniel@0: /* KERNEL_PARM is defined in svm_common.h The field 'custom' is reserved for */
Daniel@0: /* parameters of the user defined kernel. You can also access and use */
Daniel@0: /* the parameters of the other kernels. Just replace the line 
Daniel@0:              return((double)(1.0)); 
Daniel@0:    with your own kernel. */
Daniel@0: 
Daniel@0:   /* Example: The following computes the polynomial kernel. sprod_ss
Daniel@0:               computes the inner product between two sparse vectors. 
Daniel@0: 
Daniel@0:       return((CFLOAT)pow(kernel_parm->coef_lin*sprod_ss(a->words,b->words)
Daniel@0:              +kernel_parm->coef_const,(double)kernel_parm->poly_degree)); 
Daniel@0:   */
Daniel@0: 
Daniel@0: /* If you are implementing a kernel that is not based on a
Daniel@0:    feature/value representation, you might want to make use of the
Daniel@0:    field "userdefined" in SVECTOR. By default, this field will contain
Daniel@0:    whatever string you put behind a # sign in the example file. So, if
Daniel@0:    a line in your training file looks like
Daniel@0: 
Daniel@0:    -1 1:3 5:6 #abcdefg
Daniel@0: 
Daniel@0:    then the SVECTOR field "words" will contain the vector 1:3 5:6, and
Daniel@0:    "userdefined" will contain the string "abcdefg". */
Daniel@0: 
Daniel@0: double custom_kernel(KERNEL_PARM *kernel_parm, SVECTOR *a, SVECTOR *b) 
Daniel@0:      /* plug in you favorite kernel */                          
Daniel@0: {
Daniel@0:   return((double)(1.0)); 
Daniel@0: }