@Override public double calculate_K(int[] x_index,double[] x_att,int[] y_index,double[] y_att){
  double prod=a * innerproduct(x_index,x_att,y_index,y_att) + b;
  double e1=Math.exp(prod);
  double e2=Math.exp(-prod);
  return ((e1 - e2) / (e1 + e2));
}

@ Override public double calculate_K ( int [ ] x_index , double [ ] x_att , int [ ] y_index , double [ ] y_att ) { double prod = a * innerproduct ( x_index , x_att , y_index , y_att ) + b ; double e1 = Math . exp ( prod ) ; double e2 = Math . exp ( - prod ) ; return ( ( e1 - e2 ) / ( e1 + e2 ) ) ; }
calculates kernel value of vectors x and y
