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\section{Letz} \label{letz:sec}

LETZ generates a data file of z values given an expression in terms of x and y.  

\begin{verbatim}
begin letz
   data "jack.z"
   z = x+sin(y^2)/pi+10.22
   x from 0 to 30 step 1
   y from 0 to 20 step 1
end letz
\end{verbatim}

The file jack.z now contains the required data. The resulting file can be used to generate surface plots with the begin/end surface block discussed in the previous section.

