#Read data
dat <- read.table("positions.dat",sep="\t",header=FALSE)

#Have a look at the data
head(dat)

# If you failed fo order the values earlier in the exercise, 
# you can take the absolute value (abs() function) below.

d = density(dat$V1-dat$V2, kernel="gaussian")
#d = density(abs(dat$V1-dat$V2), kernel="gaussian")

# This plots the length distribution
plot(d, main="Length distribution for glimmer predictions")

# The following saves the plot in a postscript file, 
# that can be opened with the program gv.
postscript("length_plot.ps")
plot(d, main="Length distribution for glimmer predictions")
dev.off()