请教Caret包内 svmPoly 调参数问题

LYD

各位高手好，我在用caret包内的svmPoly做classification。
用默认参数运行后得到的模型提示：
Accuracy was used to select the optimal model using  the largest value.
The final values used for the model were degree = 1, scale = 0.1 and C = 1.


然后我用tuneGrid 调参数，该怎样在expand.grid内设置参数degree、scale、C的取值范围好呢。谢谢