[R] Questions bout SVM

[Nancy Adam]

Hi everyone,
Can someone please help me in these questions?:
 
1)if I use crossvalidation with svm, do I have to use this equation to 
calculate RMSE?:
      mymodel <- svm(myformula,data=mydata,cross=10)    
      sqrt(mean(mymodel$MSE)) 
But if I don’t use crossvalidation, I have to use the following to calculate 
RMSE:
      mymodel <- svm(myformula,data=mydata)           
      mytest <- predict(mymodel, mytestdata)
      error <- mytest - mytestdata[,1]
      sqrt(mean(error**2))
2)if I don’t set the parameters of SVM, like in the above, how the program 
knows them? Or it is a must to determine them when I invoke svm?
 
3)can you please tell me why we use this equation:
mymodel <- svm(myformula,data=mydata)instead of mymodel <- svm(myformula, 
mydata)                   
 
and why use this:
error <- mytest - mytestdata[,1] instead of error <- mytest – mytestdata
 
any help will be really appricaited.
Many thanks,
Nancy                                     
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