[R] puzzled with plotmath

[Claudia Beleites]

Dear all,

I'm puzzled with matrix indices in plotmath.

I'm plotting matrix elements: Z [i, i], and I'd like to put that as label. I'll 
describe what I want and what I get in LaTeX-notation.

The output should look like Z_{i, i}, and my first try was
plot (1, 1, ylab = expression (Z[i, i]))

That, however, gives me Z_{i} (no comma, no second i) although the expression 
looks OK to me:
 > a <- expression (Z[i, i])
 > a [[1]]
Z[i, i]
 > str (as.list (a [[1]]))
List of 4
  $ : symbol [
  $ : symbol Z
  $ : symbol i
  $ : symbol i

I'm able to tweak the ouput looking as I want:
plot (1, 1, ylab = expression (Z[i][", "][i]))
which is, however, logically very far from what I want to express.

What am I missing?

I'm almost sure this has been discussed before, but I can't find it: can anyone 
point me to good search terms? Is it possible to search for the terms being 
close to each other in RSiteSearch and/or RSeek? I get lots of introductory 
documents as they point to plotmath and discuss matrices...

Thanks a lot for your help,

Claudia


-- 
Claudia Beleites
Dipartimento dei Materiali e delle Risorse Naturali
Università degli Studi di Trieste
Via Alfonso Valerio 6/a
I-34127 Trieste

phone: +39 0 40 5 58-37 68
email: cbeleites at units.it