# prints the currently displayed graph to the
# file filename; suffix can be "pdf", "png" or "jpg"
# filename is a character string
pr2file <- function (filename)
{
    origdev <- dev.cur()
    parts <- strsplit(filename,".",fixed=TRUE)
    nparts <- length(parts[[1]])
    suff <- parts[[1]][nparts]
    if (suff == "pdf") {
        pdf(filename)
    }
    else if (suff == "png") {
        png(filename,bg='white')
    }
    else jpeg(filename)
    devnum <- dev.cur()
    dev.set(origdev)
    dev.copy(which = devnum)
    dev.set(devnum)
    dev.off()
    dev.set(origdev)
}