[pstricks] computed coordinates

[Michael Sharpe]

On Mar 28, 2010, at 6:30 AM, Zbigniew Nitecki wrote:

> I want to draw a series of concentric ellipses with successively larger axes.  The following
> 
> 			\begin{pspicture}(-3,-2.5)(3,3)
> 				\multido{\rc=0+0.5}{9}{\psellipse[linecolor=green](\rc,\rc\space 2 div)}
> 			\end{pspicture}
> 
> yields the error message
> 
> ! Illegal unit of measure (pt inserted).
> <to be read again> 
>                    2
> l.24 ...pse[linecolor=green](\rc,\rc\space 2 div)}
> 
> What is missing, since if instead I had written \psellipse(2,1) I would not have gotten this message?

Either of the following will work.

\multido{\rc=0+0.5}{9}{\psellipse[linecolor=green](!\rc\space \rc\space 2 div)}
\multido{\rc=0+0.5,\rd=0+.25}{9}{\psellipse[linecolor=green](\rc,\rd)}

Michael