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% Tutorial for GNUPLOT plotting program, for LaTeX users

% David Kotz

% Duke University Computer Science Department

% NOTE: If LaTeX runs out of memory processing plots,

% add ``with lines 4'' to each curve in eg*.plt and rerun make.

% some header info

\input{header}

\begin{document}

\title{\LaTeX\ and the GNUPLOT Plotting

Program\thanks{This document describes GNUPLOT version 3.0. All plots

in this document were made with that version of GNUPLOT.} }

\author{David Kotz}

\date{July 3, 1991}

\maketitle

\pagestyle{myheadings}

\markright{GNUPLOT \LaTeX\ Tutorial Version 3.0}

\currentspace % defined in header.tex

\section{Introduction and History}

GNUPLOT was originally developed by Colin Kelley and Thomas Williams

in 1986 to plot functions and data files on a variety of terminals.

In 1988 and 1989 I created an alternate version, known as Gnu\TeX,

that supported a new ``terminal type'' called {\tt latex}, so gnuplot

would output \LaTeX\ code. The plot could then be included in a

\LaTeX\ document. I added a number of embellishments, supported only

by the {\tt latex} terminal, allowing the user to produce

publication-quality plots.

In late 1989 and early 1990 Gnu\TeX\ and a number of other GNUPLOT

variants were merged together into a new release of GNUPLOT, 2.0. This

includes, among many other improvements, a \LaTeX\ driver derived from

the one in Gnu\TeX. Former Gnu\TeX\ users are referred to

Section~\ref{oldusers} for information about adapting to GNUPLOT.

Anyone interested in using GNUPLOT with \LaTeX\ should read the next

section, a tutorial, and the primary GNUPLOT manual.

The reader should note that the \LaTeX\ picture environments output by

GNUPLOT can be quite large and complicated, and can easily exceed the

memory capacity of \TeX. If an enlarged version of \TeX\ is available,

it is wise to use it. Otherwise, keep your plots simple and add

\verb+\clearpage+ to your document where necessary.

There is also a new EEPIC driver ({\tt eepic}), intended for use with

the EEPIC macro package for \LaTeX. EEPIC allows for much more

efficient line-drawing, runs through \LaTeX\ faster, and uses less

memory. See Section~\ref{s:eepic} for more information.

There is a small package of auxiliary files (makefiles and scripts)

that I find useful for making \LaTeX\ plots with GNUPLOT. This is

available for \verb+ftp+ as \verb+pub/gnuplot-latex.shar+ from

\verb+cs.duke.edu+. I can mail copies (see the end of this paper for

information).

\section{Using GNUPLOT for \LaTeX: a Tutorial}

GNUPLOT is by nature an interactive program. Users making plots for

\LaTeX\ will generally not use GNUPLOT interactively. Whenever hard

copy is desired from GNUPLOT, the program need not be run on a

graphics terminal. In this case the output is directed to a file or

pipe, then sent to the appropriate output device. For example, output

from the terminal type {\tt unixplot} may be sent to a program

interpreting the Unix plotting standard. The terminal types {\tt

imagen} and {\tt postscript} may be used for output to printers

understanding those languages. (A shell script ({\tt lasergnu}) is

supplied with the distribution that will accept a GNUPLOT command or

input file and send the output to an Imagen or Postscript laser

printer. This script may have been adapted to your site.) The terminal

type {\tt fig} outputs FIG code that can be read by the Fig graphics

program and translated into forms usable in both \TeX\ and

\LaTeX\ documents.

We now ignore the interactive nature of GNUPLOT and provide the input

to GNUPLOT from a file, \ie,

\begin{verbatim}

gnuplot gnu.input

\end{verbatim}

In this example, all of the commands to GNUPLOT are contained in the

file {\tt gnu.input}. Multiple filenames may be supplied to GNUPLOT

this way, read in the order they are given. The output (one or more

plots) may be piped to another program or redirected to a file.

Usually, however, we direct the output explicitly with an instruction

to GNUPLOT (the {\tt set output} command). GNUPLOT continues to print

error messages to the terminal (stderr).

\paragraph{Example 1:} Here is a first example, producing a plot for

this document. The GNUPLOT input file is given below, and the output

appears as Figure~\ref{eg1}. The input file defines the output to be

in \LaTeX, gives a file name for the output, and plots $y=sin(x)$ for

$x$ on $[-\pi,\pi]$. To produce the figure, I simply

\verb+\input{eg1}+ in a {\tt center} environment in a {\tt figure}

environment. In following examples, I will enclose the figure in a box

to make it look a little better.

\singlespace

\begin{verbatim}

set terminal latex

set output "eg1.tex"

plot [-3.14:3.14] sin(x)

\end{verbatim}

\currentspace

\begin{figure}[htbp]

\begin{center}

\input{eg1}

\end{center}

\caption{A first example: $y=sin(x)$}

\label{eg1}

\end{figure}

Note that GNUPLOT has drawn in the axes, labeled the tic marks for us,

scaled the $y$ axis automatically, and added a key in the

upper-right-hand corner (this may be moved with the {\tt set key}

command, and removed with {\tt set nokey}).

This is the default line style for the \LaTeX\ driver. Because of the

limited picture capabilities of \LaTeX, many dots are required to

approximate drawing a solid line. This may overload the memory of many

\TeX\ implementations. There are other line types available that draw

dotted lines and use much less memory. The EEPIC driver draws solid

lines with much less memory usage.

\paragraph{Example 2:} Now we will embellish the plot a little with

some labels. This input file produces Figure~\ref{eg2}.

\singlespace

\begin{verbatim}

set terminal latex

set output "eg2.tex"

set size 5/5., 4/3.

set format xy "$%g$"

set title "This is a plot of $y=sin(x)$"

set xlabel "This is the $x$ axis"

set ylabel "This is\\the\\$y$ axis"

plot [0:6.28] [0:1] sin(x)

\end{verbatim}

\currentspace

\boxfigure{htbp}{\fullboxwidth}{

\begin{center}

\input{eg2}

\end{center}

\caption{A more fancy example.}

\label{eg2}

}

We have specified the plot to be 5 inches wide and 4 inches tall with

the {\tt set size} command. This is the size of the area used by the

plot, {\em including} space for the labels. In the first example,

this size was the default 5 inches by 3 inches. By specifying the

scaling factors of 1 (or 5/5) and 1.3333 (or 4/3), we obtain the

desired plot size.

We have requested that the format used by the $x$- and $y$-axis tic

mark labels be in \LaTeX\ math mode. This makes the labels look a

little better. The default is \verb+set format xy "%g"+. The \verb+%g+

represents the general-purpose floating point formatting specification

for the {\tt printf} function in C. Any valid floating-point

formatting specification, or \LaTeX\ command, is allowed in the

format.

A title for the plot and labels for the axes were set up in the next

three commands. Note that they are processed by \LaTeX\ and so may

have math mode and other symbols in them. The ylabel may have multiple

lines, delineated with \verb+\\+. The ylabel can be moved around with

optional offset parameters (see {\tt set ylabel} in the GNUPLOT

manual). Typically, the ylabel needs to be moved to the left to avoid

interfering with the left-hand side of the plot. Once these labels

are set up, they will be used for all subsequent plot commands until

they are changed. These labels are also supported by the other

terminal types, but (of course) any \LaTeX\ code in the string will

not be interpreted. We have also defined the range of both $x$ (now

$[0,2\pi]$) and $y$ (here $[0,1]$).

So far we have plotted one curve, $y=\sin(x)$, on one plot. In

GNUPLOT, each {\tt plot} command generates a new plot. If the output

is to a screen, the screen is cleared. If to a printer, a new page is

produced. In the {\tt latex} case, a new picture is started. It is not

likely that \LaTeX\ users will want this to happen, so generally each

plot has its own input file and is kept in a separate output ({\tt

.tex}) file for inclusion at different places in the document.

\paragraph{Example 3:} To place more than one curve on a plot, use one

{\tt plot} statement and separate the description of each curve by a

comma. In our next example, we will plot both a function and a data

file on the same plot. This plot is shown in Figure~\ref{eg3}.

\singlespace

\begin{verbatim}

set terminal latex

set output "eg3.tex"

set format xy "$%g$"

set title "This is another plot"

set xlabel "$x$ axis"

set ylabel "$y$ axis"

set key 15,-10

plot x with lines, "eg3.dat" with linespoints

\end{verbatim}

\currentspace

\boxfigure{htbp}{\fullboxwidth}{

\begin{center}

\input{eg3}

\end{center}

\caption{An example with two curves on the same plot.}

\label{eg3}

}

Here you will see that the $x$ range was not specified. The $x$ range

is determined automatically, unless specified by the user. In

this case, it is defined by the range of the data file

\verb+"eg3.dat"+. The function is plotted over the same range. If no

data files or $x$ range are supplied, the default range of $[-10:10]$

is used. We have also moved the key to a different position. The

function $y=x$ is plotted ``with lines'', which is the default plot

style for functions, and is shown here to illustrate the plot style

option. The data file {\tt eg3.dat} is plotted with style {\tt

linespoints}, a style like {\tt lines} that also plots a symbol at

each data point.

There is a style called {\tt points} that only plots the symbols at

data points, and another called {\tt dots} that plots a tiny dot for

each data point. The {\tt points} and {\tt linespoints} styles

produce a different point symbol for each curve on the plot (for up to

twelve symbols, after which they are re-used; see

Figure~\ref{linepoint} for a complete list). The {\tt lines} and {\tt

linespoints} styles use a different line style for each curve on the

plot (in this example the dots have different spacing). The

style {\tt impulses} draws a perpendicular from each point to the

$x$-axis. Finally, the {\tt errorbars} style can draw error bars at

each data point (see the GNUPLOT manual).

\paragraph{Example 4:} In the above plots of $\sin(x)$, it would make

more sense to label the axis in units of $\pi$. The position and

labels of the tic labels may be specified by the user, with the {\tt

set xtics} and {\tt set ytics} commands. This is demonstrated by

the following example, shown in Figure~\ref{eg4}.

\singlespace

\begin{verbatim}

set terminal latex

set output "eg4.tex"

set format y "$%g$"

set format x "$%.2f$"

set title "This is $\sin(x)$"

set xlabel "This is the $x$ axis"

set ylabel "$\sin(x)$"

set nokey

set xtics -pi, pi/4

plot [-pi:pi] [-1:1] sin(x)

\end{verbatim}

\currentspace

\boxfigure{htbp}{\fullboxwidth}{

\begin{center}

\input{eg4}

\end{center}

\caption{An example of the {\tt set xtics} command.}

\label{eg4}

}

Since {\tt pi} is a predefined variable in GNUPLOT, we can use it

anywhere we may use an expression. The {\tt set xtics} command here

specifies that the tics on the $x$ axis start at $-\pi$ and increment

by $\pi/4$. Since no end point is given, the tics continue to the

right edge. We have also turned off the key, and changed the format to

restrict the $x$-axis tic labels to 2 decimal places.

With a little more work, the plot can look even better. Another form

of this command allows us to specify the label and position of each

tic individually. Replacing the above {\tt set xtics} command with

the following gives us Figure~\ref{eg5}. We also make use of the line

continuation character, the backslash (\verb+\+), to spread out this

command for readability.

\singlespace

\begin{verbatim}

set xtics ("$-\pi$" -pi,\

"$-\frac{\pi}{2}$" -pi/2,\

"0" 0,\

"$\frac{\pi}{2}$" pi/2,\

"$\pi$" pi)

\end{verbatim}

\currentspace

\boxfigure{htbp}{\fullboxwidth}{

\begin{center}

\input{eg5}

\end{center}

\caption{A fancy example of the {\tt set xtics} command.}

\label{eg5}

}

\paragraph{Going further:} You should now be able to make a variety of

plots for your \LaTeX\ document. We will present a final example

without explanation that showcases some of the capabilities of

GNUPLOT. You may find documentation for the various commands in the

GNUPLOT manual, though hopefully this example is somewhat

self-explanatory. This is shown in Figure~\ref{eg6}.

\singlespace

\begin{verbatim}

set terminal latex

set output "eg6.tex"

set size 3.5/5, 3/3.

set format y "$%g$"

set format x "$%5.1f\mu$"

set title "This is a title"

set xlabel "This is the $x$ axis"

set ylabel "This is\\a longer\\version\\ of\\the $y$\\ axis"

set label "Data" at -5,-5 right

set arrow from -5,-5 to -3.3,-6.7

set key -4,8

set xtic -10,5,10

plot [-10:10] [-10:10] "eg3.dat" title "Data File" with linespoints 1 7,\

3*exp(-x*x)+1 title "$3e^{-x^{2}}+1$" with lines 4

\end{verbatim}

\currentspace

\boxfigure{htbp}{\fullboxwidth}{

\begin{center}

\input{eg6}

\end{center}

\caption{An example of many features.}

\label{eg6}

}

\paragraph{Line and point types:} For reference, we show all of the

line and point types available in Figure~\ref{linepoint}.

\boxfigure{htbp}{\fullboxwidth}{

\begin{center}

\input{linepoin}

\end{center}

\caption{All of the line and point types in the \LaTeX\ driver.}

\label{linepoint}

}

\subsection{Summary --- Use with \LaTeX}

In summary, to use the \LaTeX\ facilities of GNUPLOT, the first

command to GNUPLOT should be

\begin{syntax}

set terminal latex

\end{syntax}

and the output of GNUPLOT should be directed to a file, for example,

\begin{verbatim}

set output "plot.tex"

\end{verbatim}

This may be anything you like but it should have a {\tt .tex} extension,

of course. Then the size of the plot should be given. For example, the

command

\begin{verbatim}

set size 1,2

\end{verbatim}

tells GNUPLOT to use a 5 inch wide by 6 inch high box for the plot.

The numbers given are {\em scale factors}, not the actual size. The

default is 5 inches by 3 inches. This is the size of the complete

plot, including all labels.

When finished, the file will contain all of the plots you have

specified (you probably only want one plot per file). This file can

then be used in a \LaTeX\ document, \eg,

\singlespace

\begin{verbatim}

\begin {figure}

\begin{center}

\input{plot}

\end{center}

\end {figure}

\end{verbatim}

\currentspace

This puts the plot into a figure.

You will also want to read about the following commands: {\tt set

title, set xlabel, set ylabel, set key, set label, set xtics, set

ytics}, and {\tt set clip}. These are all described in the regular

GNUPLOT manual.

\section{Use with EEPIC}

\label{s:eepic}

EEPIC is a macro package extending the picture environment of \LaTeX.

If you have the EPIC or EEPIC macros, and your {\tt dvi} translator

supports the {\em tpic\/} \verb+\special+s, then you can save \LaTeX\

memory. With EEPIC pictures, the {\tt plot.tex} file will be smaller,

\LaTeX\ will run much faster (and need much less memory), and the {\tt

dvi} file will be smaller. The quality of the output is about the

same. If you change the source, you can generate some more interesting

line styles.

To use EEPIC, set GNUPLOT's terminal type to {\tt eepic} instead of

{\tt latex}, and use GNUPLOT as before. The line styles will change.

Include the file {\tt plot.tex} in your document as before, along with

the document style options {\tt [epic,eepic]}.

\section{For Former Gnu\TeX\ Users}

\label{oldusers}

Former Gnu\TeX\ users may be pleased with many of the new features

(many inspired by your suggestions!), but will also find many changes.

GNUPLOT will {\em not\/} run all Gnu\TeX\ input files unchanged.

Several Gnu\TeX\ features were not included in GNUPLOT because they

were specific to the \LaTeX\ driver. I encourage you to use the newer

GNUPLOT. A translator is available that attempts to translate your

old Gnu\TeX\ 1.6 input files into GNUPLOT 3.0 files. You can ftp it

from \verb+cs.duke.edu+ as \verb+dist/sources/gnuplot/gnut2p.tar.Z+.

This file also contains directions and a list of changes from Gnu\TeX\

to GNUPLOT.

\section{Contact}

For general GNUPLOT questions, send mail to the GNUPLOT mailing list

(\verb+info-gnuplot@dartmouth.edu+) or post to the GNUPLOT newsgroup

(\verb+comp.graphics.apps.gnuplot+).

\end{document}

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