[R] need help with pdf-plot

[Antje]

Hello,

I'm trying to plot a set of barplots like a matrix (2 rows, 10 columns 
from"reduced_mat") to a pdf. It works with the following parameters:

pdf("test.pdf",width=ncol(reduced_mat)*2, height=nrow(reduced_mat)*2, pointsize 
= 12)

par(mfcol = c(nrow(reduced_mat),ncol(reduced_mat)), oma = c(0,0,0,0), 
lwd=48/96, cex.axis = 0.5, las = 2, cex.main = 1.0)

The I get a long narrow page format with the quadratic barplots.

But I would like to have a A4 format in the end and the plots not filling the 
whole page (they should stay somehow quadratic and not be stretched...).

What shall I look for to achieve this?

Antje