Personally, I find it easier to fix the overall size of the "page" and 
modify the margins in line size (mar and oma rather than mai and omi), 
until I get the plots the way I want them.  You don't specify what OS 
you're using, but in windows, I would use something like

windows(h=16, w=9)
par(mfrow=c(4, 2), oma=c(2, 2, 2, 2), mar=c(2, 2, 2, 2))

I'm not sure why you're writing
mtext("testen")
for each plot when you already specify
main="test"
in the hist() function.
Did you want an overall title on the page?
If so, you could try ...

hist(islands, freq=FALSE,col="blue",main="test 1") 
hist(islands, freq=FALSE,col="blue",main="test 2") 
hist(islands, freq=FALSE,col="blue",main="test 3") 
hist(islands, freq=FALSE,col="blue",main="test 4") 
hist(islands, freq=FALSE,col="blue",main="test 5") 
hist(islands, freq=FALSE,col="blue",main="test 6") 
hist(islands, freq=FALSE,col="blue",main="test 7") 
hist(islands, freq=FALSE,col="blue",main="test 8") 
mtext("testen", outer=TRUE)

Hope this helps.

Jean



Nerak wrote on 03/13/2012 04:24:42 AM:

> Hi all,
> I have a basic question concerning graphs in R.  I?m using the par()
> function and I?m working with multiple figures by row (mfrow) but my the
> hight of my figures become compressed. I have 4 rows and 2 columns 
(because
> I want to plot 8 histograms (freq = FALSE ) on it. I know I can adapt my
> margins with for example ?oma? and ?mai? but I don?t know how to choose 
the
> size of the figure? I read something about pin. That this should go 
about
> ?the current plot dimensions, (width, height), in inches. But I don?t 
know
> which values I should use. Because I always get the remark ?plot region 
too
> large?.
> 
> I would like to have for example figures of 5,8 by 5,8 cm (is 2,3 by 2,3
> inches I think). But I don?t know how to specify this?. I'm getting lost
> with the par() function
> 
> Hard to give my data online for a reproducible example but with for 
example
> this, I have the same problems:
> 
> par(mfrow=c(4,2),oma=c(2,2,2,2), mai=c(0.6, 0.6, 0.6, 0.6))
> hist(islands, freq=FALSE,col="blue",main="test")
> mtext("testen")
> hist(islands, freq=FALSE,col="blue",main="test")
> mtext("testen")
> hist(islands, freq=FALSE,col="blue",main="test")
> mtext("testen")
> hist(islands, freq=FALSE,col="blue",main="test")
> mtext("testen")
> hist(islands, freq=FALSE,col="blue",main="test")
> mtext("testen")
> hist(islands, freq=FALSE,col="blue",main="test")
> mtext("testen")
> hist(islands, freq=FALSE,col="blue",main="test")
> mtext("testen")
> hist(islands, freq=FALSE,col="blue",main="test")
> mtext("testen") 
> 
> (normally, I specify my breaks, ylab and xlab, xlim and y lim)
> 
> I hope someone can help me.
> Many thanks,
> Nerak
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