There are 20 kernels supported. Belows are the kernels when given two vectors \(x,y\), \(K(x,y)\)
- linear
\(=<x,y>+c\)
- polynomial
\(=(<x,y>+c)^d\)
- gaussian
\(=exp(-c\|x-y\|^2)\), \(c>0\)
- laplacian
\(=exp(-c\|x-y\|)\), \(c>0\)
- anova
\(=\sum_k exp(-c(x_k-y_k)^2)^d\), \(c>0,d\ge 1\)
- sigmoid
\(=tanh(a<x,y>+b)\)
- rational quadratic
\(=1-(\|x-y\|^2)/(\|x-y\|^2+c)\)
- multiquadric
\(=\sqrt{\|x-y\|^2 + c^2}\)
- inverse quadric
\(=1/(\|x-y\|^2+c^2)\)
- inverse multiquadric
\(=1/\sqrt{\|x-y\|^2+c^2}\)
- circular
\(=
\frac{2}{\pi} arccos(-\frac{\|x-y\|}{c}) - \frac{2}{\pi} \frac{\|x-y\|}{c}\sqrt{1-(\|x-y\|/c)^2}
\), \(c>0\)
- spherical
\(=
1-1.5\frac{\|x-y\|}{c}+0.5(\|x-y\|/c)^3
\), \(c>0\)
- power/triangular
\(=-\|x-y\|^d\), \(d\ge 1\)
- log
\(=-\log (\|x-y\|^d+1)\)
- spline
\(=
\prod_i (
1+x_i y_i(1+min(x_i,y_i)) - \frac{x_i + y_i}{2} min(x_i,y_i)^2
+ \frac{min(x_i,y_i)^3}{3}
)
\)
- Cauchy
\(=\frac{c^2}{c^2+\|x-y\|^2}\)
- Chi-squared
\(=\sum_i \frac{2x_i y_i}{x_i+y_i}\)
- histogram intersection
\(=\sum_i min(x_i,y_i)\)
- generalized histogram intersection
\(=sum_i min(
|x_i|^c,|y_i|^d
)\)
- generalized Student-t
\(=1/(1+\|x-y\|^d)\), \(d\ge 1\)