[pstricks] variables and pstricks.

[Eduardo]

Hi Alan, 

> This isn't very transparent 

For sure, it isn't. 

> but it seems to do the job. 

I got a message error: 
! Missing number, treated as zero.
<to be read again>
                   R
l.147 \pscircle(0,0){R}

Maybe a '!' sign missing somewhere. Anyway, I'd like to use 
variables in a general case: a=2, b=0.5, c=a+b, etc. 

Regards, 

Eduardo.