Exporting to file: passing source name to file name in loop

Hi,

I'm having a mental block as to how I can automatically assign filenames
to the output of the following code. I am wishing to create a separate
.png file for every image created, each of them having a sequential
filename ie "sourcefile_index.png" so that I can create a movie from
them.

Please could someone tell me where I am going wrong?

the following code works fine and outputs to screen:

fun_pca_vector_movie_plot<-function(x,y,z,t){
zz=seq(1,(nrow(x)-t),by=t);jj=seq(t+1,(nrow(x)),by=t)
for(i in seq(along=zz)){
        pca<-prcomp(x[zz[i]:jj[i],], retx=T, center=T,scale=T)
       {
    par(mfrow=c(1,z))
     for(i in 1:z){
      image(east,north,t(map.matrix),col=my.colors,axes=T,
          xlab="",ylab="")
      text(y[,3],y[,2],labels=as.character(y[,1]))
      title(paste("Component",i,"Step:"))
       arrows(y[,3],y[,2],(y[,3]+50*(pca$rotation[i,1:(ncol(x)/2)])),
       (y[,2]+50*(pca$rotation[i,((ncol(x)/2)+1):(ncol(x))])),
       angle=30,length=0.05,code=2)
     }
    box()
   }
  }}

but when I try to save to file as follows it doesn't work:

fun_pca_vector_movie_plot<-function(x,y,z,t){
zz=seq(1,(nrow(x)-t),by=t);jj=seq(t+1,(nrow(x)),by=t)
for(i in seq(along=zz)){
     pca<-prcomp(x[zz[i]:jj[i],], retx=T, center=T,scale=T)
   {
    par(mfrow=c(1,z))
      for(i in 1:z){
      plot.new()
      png(file=(paste(x".",i,"_",zz,".png",sep="")),width=240,height=240)
      image(east,north,t(map.matrix),col=my.colors,axes=T,
          xlab="",ylab="")
      text(y[,3],y[,2],labels=as.character(y[,1]))
      title(paste("Component",i,"Step:"))
       arrows(y[,3],y[,2],(y[,3]+50*(pca$rotation[i,1:(ncol(x)/2)])),
       (y[,2]+50*(pca$rotation[i,((ncol(x)/2)+1):(ncol(x))])),
       angle=30,length=0.05,code=2)
      dev.off()
     }
    box()
   }
  }}

many thanks in advance!
Laura Quinn
Institute of Atmospheric Science
School of Earth and Environment
University of Leeds
Leeds
LS2 9JT

tel: +44 113 343 1596
fax: +44 113 343 6716
mail: laura at env.leeds.ac.uk