[R] Help with plotmath

[Steve Roberts]

There must be a simple answer. I want to plot an expression, 
where the expression is held in a string variable. The "obvious" 
solution along the lines of

ex<-"x^2"
plot( c(0,1), c(0,1), main=as.expression(ex) )

gives me the a title x^2 - ie doesn't treat it like an expression. I 
suspect I don't understand expressions properly. For the real 
problem I do need to have my expression string in a variable as it is 
data-dependent. 

Can someone tell me the magic words?

Steve
  Dr Steve Roberts 
  steve.roberts at man.ac.uk

Senior Lecturer in Medical Statistics,
CMMCH NHS Trust and University of Manchester Biostatistics Group,
0161 275 5192 / 0161 276 5785