Accurate Multisteps Traffic Flow Prediction Based on SVM

Table 1

Four popular kernel functions.

Kernel function	Expression	Comment
Linear kernel	𝐾(𝑥𝑖,𝑥𝑗)=𝑥^𝑇𝑖𝑥𝑗
Polynomial kernel	𝐾(𝑥𝑖,𝑥𝑗)=(𝛾𝑥^𝑇𝑖𝑥𝑗+𝑟)^𝑑	𝛾>0
Radial basis function (RBF) kernel	𝐾(𝑥𝑖,𝑥𝑗)=𝑒^−𝛾‖𝑥𝑖−𝑥𝑗‖2	𝛾>0
Sigmoid kernel	𝐾𝑥𝑖,𝑥𝑗=tanh𝛾𝑥^𝑇𝑖𝑥𝑗+𝑟^𝑑

𝑥_𝑖, 𝑥_𝑗 are input vectors and 𝛾, 𝑟, and 𝑑 are kernel parameters.