$$\begin{array}{rl}\underset{w,b,\xi ,{\xi }^{*}}{\min }& \frac{1}{2}{w}^{T}w+C\sum _{i=1}^n({\xi }_i+{\xi }_i^{*})\\ \text{subject to }& y_i-f(x_i)\le ϵ+{\xi }_i,\\ & f(x_i)-y_i\le ϵ+{\xi }_i^{*},\\ & {\xi }_i,{\xi }_i^{*}\ge 0,i=1,\dots ,n\end{array}$$