[R] Same scale on different q-q plots

[Dr. Enrique Hernández Lemus]

Hi there, I'm new on the list. I am wondering as how to make different q-q
plots and display them on the same scale in order to attain an easy visual
comparison.

I have tried to use xlim and ylim as arguments to qq.plot in a similar
fashion to what is done on plot, also I have tried to use the plot.window
utility to implement xlim and ylim. I have even modified the qq.plot.R
source and re-compiled but none of these efforts has given any result.

I am doing a sequence of steps like the following:

library(car)
 p<-read.csv("inputP",header=T)
 p <- apply(p,c(1,2),as.numeric)
 q<-qchisq(1-p,2)

 png(file="outputP.png", bg="transparent")
plot.window(xlim=c(0,50), ylim=c(0,50))
qq.plot(q, dist="chisq", df=2)
 y<-rchisq(length(p),2)
 lines(y,y)
 dev.off()


Is there anything that I can do to produce several q-q plots from
different data and put them in the same scale, say x-values in (0-50) and
y-values in (0-50)?

Thank you to all in advance

-- 
Dr. Enrique Hernández Lemus
Medical Sciences Researcher "B"
Computational Genomics
Phone: 5350-1970
Fax: 5350-1999
Email: ehernandez at inmegen.gob.mx