Table 1. The expression of several classes of kernels.

Name	Caculation
Linear	K(x,y) = x × y
Polynomial	K(x,y) = (ax × y + b)d
RBF	K(x,y) = exp(−|x−y|2)/δ2
Sigmoid	K(x,y) = 1/(1 + exp(−|x−y|))