Plotmath bug or my misunderstanding?

Date: Sat, 12 May 2012 14:05:26 -0700
From: Bert Gunter<gunter.berton at gene.com>
To:r-help at r-project.org
Subject: [R] Plotmath bug or my misunderstanding?
Message-ID:
	<CACk-te0syHj9XjbkfHPYtCMwyWtYdPFYCehxGpxidtBR0_PkdQ at mail.gmail.com>
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This is a followup to a recent post on using atop() to obtain
multiline expressions.

My reading of the plotmath docs makes it clear that issuing (in base
graphics) the specification

par(cex = 2)

doubles symbols and regular text in subsequent plotmath expressions.
However, it is unclear to me what specifying cex_within_  the
annotation function using plotmath should do, and the following seems
to want to have it both ways: ignore/obey )or maybe recycle?)

plot(1,type="n", xaxt='n', yaxt='n', ann=FALSE)
  text(1,1,labels=expression(atop(sigma,"some text")),cex = 2)
## obeys the cex specification in symbols and text

HOWEVER

plot(1,type="n", xaxt='n', yaxt='n', ann=FALSE)
  text(1,1,labels=expression(atop(atop(sigma,"some text"),"another
level")),cex = 2)
## ???

For even more fun, try:

plot(1,type="n", xaxt='n', yaxt='n', ann=FALSE)
  text(1,1,labels=expression(atop(atop(sigma,"some text"),"another
level")),cex = 1:2)
##????

So I confess to being flummoxed. Enlightenment would be much appreciated.

Cheers,
Bert