[R] SVM - calculating values problem

Sarah Goslee @@r@h@go@|ee @end|ng |rom gm@||@com
Wed Aug 28 12:50:02 CEST 2019

You could download the package code from CRAN and look yourself at what the
predict function is doing.


On Wed, Aug 28, 2019 at 6:35 AM PELE Benoît (Acoss) <benoit.pele using acoss.fr>

> Hello everybody,
> That is the first time that I am working on a SVM modeling and I would
> like to calculate by myself the result values from the SVM for each line of
> my database (named x_appr_svm).
> First I tested a linear SVM model using the e1071 package and to calculate
> the individual results by myself I did the next things :
> Retrieving the model coefficients  : coef_svm<-t(svm$coefs) %*%
> x_appr_svm[svm$index,]
> Calculating the values for each line : p2<-x_appr_svm %*% t(coef_svm) -
> svm$rho
> Using the predict function to compare : p1<-attr(predict(object=svm,
> newdata=x_appr_svm, decision.values=T), "decision.values")
> --> p1 and p2 are the same.
> Next I tested a polynomial SVM model using the same package and the same
> method knowing that the model parameters are :
> degree=2,  gamma=0.02, coef0=0.01
> The calculation of the individual values becomes (I guess) :
> p2<-(0.02*x_appr_svm %*% t(coef_svm)+0.01)^2-svm$rho
> --> p1 and p2 are really different!
> Despite of my searching, I do not understand why or where is the problem
> in my second p2 formula. Do you see the mistake?
> Thank you for your help and have a good day, Benoit (France).
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Sarah Goslee (she/her)

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