examination of how sigma parameters in RBF kernel affect results.

RBF_sigma_test.R

# ガウスカーネルのσパラメータの意味を調べるテスト
# examination of how sigma parameters in RBF kernel affect results.
# resulting image is,
# http://dl.dropbox.com/u/15259519/images/RBF_sigma.swf
sr <- function() source('RBF_sigma_test.R')

library(kernlab)

N <<- 100
sigmas <<- c(0.0001,0.0005,0.001,0.005,0.01,0.05,0.1,0.5,1,5,10,50)

space <- function(n) {
  s<-''; for (i in 1:n) s<-paste(s,' ',sep=''); return(s)
}

plot1<-function(x,y,r,rc) {
	plot(x,y)
	par(new=T)
	plot(x,r,type='n',axes=F)
	text(x,r,substr(rc,0,1))
	title(main='y=sin(x)')
}

plot2<-function(sigma,k,df) {
	plot(k,data=df)
	title(main=paste(space(55),'σ =',sigma))
}

main<-function() {
	x<-seq(0,2*pi,length=N)
	y<-sin(x)
	r<-runif(N,-1,1)
	r_class<-factor(r>=y)

        plot1(x,y,r,r_class); 
	png(file='sin_x.png',width=640,height=480)
        plot1(x,y,r,r_class)
        dev.off()

	df<-data.frame(x=x,y=r)
	for (sigma in sigmas) {
          readline('please enter key to proceed, ...')

	  k <- ksvm(r_class~r+x,kernel='rbfdot',kpar=list(sigma=sigma))
	  plot2(sigma,k,df)

	  file<-paste('RBF_sigma_',sigma,sep='')
	  file<-sub("[.]","_",file)
	  file<-paste(file,'png',sep='.')
	  print(paste("write to",file))
	  png(file=file,width=640,height=480);
	  plot2(sigma,k,df)
	  dev.off()
	}
}

main()