multiple lines on multiple plots

From: James Annan <jdannan at jamstec.go.jp>
Subject: [R] multiple lines on multiple plots
To: r-help at r-project.org
Received: Tuesday, April 12, 2011, 9:30 AM
I'm sure this must be trivial, but
I'm a novice with R and can't work out how to handle the
axes when I am constructing multiple plots on a page and try
to return to a previous one to put multiple data sets it.

A simple example:
---
x<- 1:10
y<- (1:100)*3
par(mfcol=c(2,1))
plot(x)
plot(y)

par(mfg=c(1,1))
lines(x)
---

The first 5 lines make two plots with a row of dots along
the diagonal of each. I intended the last two statements to
add a line to the first plot, that runs along the same data
points already plotted there. However, although the commands
add a line to the top plot, it is clearly using the axis
dimensions of the lower plot. Can someone tell me how to get
it to use the axes that are already there?

Variants like lines(x,xlim=c(1,10)) have no effect.

Thanks in advance for any help.

James
-- James D Annan jdannan at jamstec.go.jp
Tel: +81-45-778-5618 (Fax 5707)
Senior Scientist, Research Institute for Global Change,
JAMSTEC
(The Institute formerly known as Frontier)
Yokohama Institute for Earth Sciences, 3173-25 Showamachi,
Kanazawa-ku, Yokohama City, Kanagawa, 236-0001 Japan
http://www.jamstec.go.jp/frcgc/research/d5/jdannan/