legend at fixed distance form the bottom

-----Original Message-----
From: r-help-bounces at r-project.org [mailto:r-help-bounces at r-
project.org] On Behalf Of Christophe Genolini
Sent: Friday, December 05, 2008 6:40 AM
To: r-help at r-project.org
Subject: [R] legend at fixed distance form the bottom

Hi the list

I would like to add a legend under a graph but at a fixed distance from
the graphe. Is it possible ?
More precisely, here is my code :

--- 8< ----
symboles <- c(3,4,5,6)
dn <- rbind(matrix(rnorm(20),,5),matrix(rnorm(20,2),,5))
listSymboles <- rep(symboles,each=2)
matplot(t(dn),pch=listSymboles,type="b")
legend("bottom", pch = unique(listSymboles), legend = c("ane",
"cheval",
"poney", "mule"), inset = c(0,-0.175), horiz = TRUE, xpd = NA)
--- 8< ----

But when I change the size of the graph, the legend is misplaced.

Instead, I try to put some text in xlab, but I do not know how to get
the +, x , V and other symbol.
Does anyone got a solution ?

Thanks a lot.

Christophe