Thank you so much! I will have a try!! ~ maggie On Dec 27, 2007 6:43 PM, Uwe Ligges <[EMAIL PROTECTED]> wrote:
> > > Maggie Wang wrote: > > Hi, Uwe, > > > > Thanks for the reply!! I have 87 observations in total. If this amount > > causes the different best.parameters, is there a better way than cross > > validation to tune them? > > > In order to get stable (I do not say "best") results, you could try some > bootstrap with many replications or leave-one-out crossvalidation. > > Uwe > > > Thank you so much for the help! > > > > Best Regards, > > Maggie > > > > On Dec 27, 2007 6:17 PM, Uwe Ligges <[EMAIL PROTECTED]> > > wrote: > > > >> > >> Maggie Wang wrote: > >>> Hi, > >>> > >>> I run the following tuning function for svm. It's very strange that > >> every > >>> time i run this function, the best.parameters give different values. > >>> > >>> [A] > >>> > >>>> svm.tune <- tune(svm, train.x, train.y, > >>> validation.x=train.x, validation.y=train.y, > >>> > >>> ranges = list(gamma = 2^(-1:2), > >>> > >>> cost = 2^(-3:2))) > >>> > >>> > >>> > >>> # where train.x and train.y are matrix specified. > >>> > >>> > >>> > >>> # output command: > >>> > >>> > >>> > >>>> svm.tune$best.parameters$cost > >>>> svm.tune$best.parameters$gamma > >>> > >>> > >>> result: > >>> > >>> cost gamma > >>> 0.25 4.00 > >>> > >>> > >>> > >>> run A again: > >>> > >>> cost gamma > >>> 1 4 > >>> > >>> > >>> > >>> again: > >>> > >>> cost gamma > >>> 0.25 4.00 > >>> > >>> > >>> > >>> The result is so unstable, if it varies so much, why do we need to > tune? > >> Do > >>> you know if this behavior is normal? Can we trust the > best.parametersfor > >>> prediction? > >> I guess you do not have really many observations in your dataset. Then > >> it highly depends ion the cross validation sets which parameter is > best. > >> And therefore you get quite different results. > >> > >> Uwe Ligges > >> > >> > >> > >>> > >>> Thank you so much to help out!! > >>> > >>> > >>> > >>> Best Regards, > >>> > >>> Maggie > >>> > >>> [[alternative HTML version deleted]] > >>> > >>> ______________________________________________ > >>> R-help@r-project.org mailing list > >>> https://stat.ethz.ch/mailman/listinfo/r-help > >>> PLEASE do read the posting guide > >> http://www.R-project.org/posting-guide.html<http://www.r-project.org/posting-guide.html> > <http://www.r-project.org/posting-guide.html> > >>> and provide commented, minimal, self-contained, reproducible code. > > > [[alternative HTML version deleted]] ______________________________________________ R-help@r-project.org mailing list https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide http://www.R-project.org/posting-guide.html and provide commented, minimal, self-contained, reproducible code.
