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\begin{center}
\bf Catalyst Interaction Plot with S
\end{center}

\noindent
Here is a way to get nice interaction plots with S.  The {\tt
catalyst} example from {\em Statistical Models in S} by Chambers and
Hastie (1992) is used to illustrate concepts.  The
file that created this document is called {\tt catalyst.tex}\ .
\\\\
{\bf 1. Turn on a graphics driver.}  On an X-window (e.g.\ NCD terminal),
use the graphics device {\tt x11()} (for S) or {\tt motif()} (for
Splus), or on a dumb keyboard terminal use {\tt printer()}.  Mac and
PC platforms having a ``tektronics'' emulator might try the graphics
device {\tt tek4014()}.  Note that only one graphics device can be on
at a time; calling a second one turns off the first.
\\\\
{\bf 2. Play around interactively with plots in S.}  Do this until you
find what you want. Try my {\tt lsd.plot} as an alternative to {\tt
interaction.plot} (but you must first call {\tt library(pda)}).
\\\\
{\bf 3. Construct a file of plot commands.} This helps keeps track of
plots that work well.  Build ideas interactively in S, using a
separate editing window or invoking an editor from within S (e.g.\
{\tt !emacs catplot.s}) to update your file. Here is my file {\tt
catplot.s}:
\begin{verbatim}
motif()
par(mfcol=c(1,2))
plot(catalyst)
attach(catalyst)
interaction.plot(Conc, Cat, Yield)
detach("catalyst")
\end{verbatim}
{\bf 4. Turn on the {\tt postscript()} device driver.}  This saves
the plot in a postscript file.  Use the {\tt postscript} command
defaults if you want to have a full page plot, or change the {\tt
height}, {\tt width} and {\tt pointsize} for smaller plots for
reports.  Source your plot commands.  Then turn off the graphics
device with {\tt graphics.off()} (or reinvoke your favorite) to close
the postscript file, called {\tt catplot.ps} here.

\begin{verbatim}
postscript("catplot.ps",height=4,width=6,pointsize=10,horizontal=F)
source("catplot.s")
dev.off()
\end{verbatim}

\noindent
{\bf 5. Examine the plots.}  The figure on the next page was plotted
with the following commands:

\begin{verbatim}
   \begin{figure}[htb]
      \centerline{\psfig{figure=catplot.ps}}
      \caption{Catalyst Main Effects and Interactions}
   \end{figure}
\end{verbatim}

% here are the actual plot commands for LaTeX:
   \begin{figure}[htb]
      \centerline{\psfig{figure=catplot.ps}}
      \caption{Catalyst Main Effects and Interactions}
   \end{figure}
{\bf 6. View the PostScript plot.}
There is a {\tt ghostview()} command (as well {\tt lpr()},
{\tt lpq()} and {\tt enscript()}) in the {\tt library(pda)} to make
viewing and printing easier:
\begin{verbatim}
> library(pda)
> ghostview("catplot.ps")
# if it looks OK and you can print it from within ghostview
# or send it to laserprinter with lpr
> lpr("catplot.ps")
# check the printer queue
> lpq()
\end{verbatim}
Note: {\tt ghostview} takes a moment to display your graphics.  The
{\tt ghostview()} command in S stays active by default.
You can update your postscript file and reopen it.
\\\\
{\bf 7. Examine the \LaTeX\ source for this document.}
You may want to learn how to embed plots in your reports.  See this
file ({\tt catalyst.tex}) for an example.  Once you have made created
{\tt catplot.ps}, and have the file {\tt catalyst.tex}, do the
following (from UNIX, not S!):
\begin{verbatim}
% latex catalyst
% dvips catalyst
% ghostview catalyst.ps
\end{verbatim}
The command {\tt dvips} converts {\tt catalyst.dvi} to a PostScript
file {\tt catalyst.ps}.  (You must specify the {\tt .ps} ending for
{\tt ghostview}.)  The document viewer {\tt xdvi} can examine {\tt
catalyst.dvi} directly:
\begin{verbatim}
% xdvi catalyst
\end{verbatim}
{\bf 8. Print the PostScript document.}
When you are satisfied with your plot and document, you can send it to
the printer if you have not done this from within {\tt ghostview}\,.
The UNIX command is either
\begin{verbatim}
% dvipr catalyst
\end{verbatim}
or, if you used {\tt dvips} to create a PostScript file,
\begin{verbatim}
% lpr catalyst.ps
\end{verbatim}
{\bf WARNING:} Postscript files take space.  Delete them if not
needed.
\\\\
{\bf 9. Translate PostScript to GIF or JPEG.}
The {\tt xv} command can be used on an X terminal to translate {\tt
catplot.ps} into {\tt catplot.gif} or {\tt catplot.jpeg} which can be
embedded in Word documents on Macs or Windows systems. Type
\begin{verbatim}
% xv catplot.ps
\end{verbatim}
Once the image is up, click the right mouse button for the menu.

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