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{\Large \bf \LaTeX\ and the Gnuplot Plotting Program}

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{\bf David Kotz} \\[0.4cm]

Principal author of this tutorial for gnuplot 3.0, July 3, 1991 \\[1.0cm]

{\bf current gnuplot team} \\[0.4cm]

Updates of this tutorial for gnuplot 4.0, March 2004 \\

Update of this tutorial for gnuplot 4.2, August 2006 \\

Update of this tutorial for gnuplot 4.4, September 2010 \\

Update of this tutorial for gnuplot 4.6, February 2012

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\markright{Gnuplot \LaTeX\ Tutorial Version 4.6}

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\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.

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 an 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.

Other gnuplot terminal types have been added that take advantage of

newer \TeX\ and \LaTeX\ packages and variants, including {\tt emtex},

{\tt metafont}, {\tt epslatex}, {\tt tikz}, and {\tt context}.

\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.

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

to gnuplot from a file, \ie,

\begin{verbatim}

\end{verbatim}

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

file {\tt plotcommands.gp}. 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 "outfile.tex"} command). Gnuplot continues to

print error messages to the terminal (stderr). After printing, the output file

has to be closed by {\tt set output}, \ie{} without the file name specification.

\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.

\begin{verbatim}

\end{verbatim}

\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 unset key}%

\footnote{In gnuplot version 4.0, the syntax {\tt set noXXX} changed to

{\tt unset XXX}.}).

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}.

\begin{verbatim}

\end{verbatim}

\begin{figure}[htbp]

\begin{center}

\input{eg2}

\end{center}

\caption{A fancier example.}

\label{eg2}

\end{figure}

We have specified the plot to be 7 cm wide and 5 cm tall with

the {\tt set term latex 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.

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}.

\begin{verbatim}

\end{verbatim}

\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{testcomp} 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}.

\begin{verbatim}

\end{verbatim}

\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. Note that the

y axis label was delimited by double quotes, so the

backslash had to be escaped. Within single quotes, as in the title,

gnuplot passes the backslashes through with no changes.

(The exception: a backslash at the end of a line---even within single

quotes---is used by gnuplot for line continuation.)

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.

\begin{verbatim}

\end{verbatim}

\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}.

\begin{verbatim}

\end{verbatim}

\begin{figure}

\begin{center}

\input{eg6}

\end{center}

\caption{An example of many features.}

\label{eg6}

\end{figure}

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

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

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

In summary, to use the most basic \LaTeX\ mode 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}

\end{verbatim}

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

of course. The default plot size is 5 inches by 3 inches.

You can change this be specifying a size in either cm or inches when

you select the terminal

\begin{syntax}

set terminal latex size 7cm, 5cm

\end{syntax}

Then you do the (s)plot, and finally issue commands to close the file and

switch the terminal back to the default by

\begin{verbatim}

\end{verbatim}

Finally, 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,

\begin{verbatim}

\end{verbatim}

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{Other \TeX-based terminal types in gnuplot}

In addition to the \texttt{latex} terminal, the following \LaTeX-friendly

terminals are available. The gnuplot documentation contains more information

about the options and usage for each of these.

\begin{itemize}

\item \texttt{emtex}: Like the \texttt{latex} terminal, but supports emtex

specials: any line slopes contrary to a very limited set of \LaTeX{} slopes.

\item \texttt{epslatex}: Combined \LaTeX{} and postscript parts for text and

lines, respectively, with the postscript part included by

\verb+\includegraphics{...}+ command.

\item \texttt{pstex} and \texttt{pslatex}: Combined \TeX{} / \LaTeX{} and

postscript parts for text and lines, respectively, included by

\verb+\special{psfile=...}+ command.

\item \texttt{mf} and \texttt{mp}: Produces metafont and metapost outputs.

\item \texttt{pslatex and epslatex}: New versions of these terminals were

introduced in gnuplot 4.4. See the example below.

\item \texttt{tikz}: Much improved graphics compaired to earlier \LaTeX terminals.

Use of the terminal requires a lua interpreter that is called by gnuplot.

The resulting .tex file can be processed using pdflatex.

\item \texttt{context}: Produces output for the {Con{\TeX}t} environment.

\end{itemize}

The {\tt tikz} and {\tt context} terminals support newer gnuplot features

such as transparency and embedded images. The {\em standalone} terminal

option allows you to create a *.tex document that can be processed by itself

without being embedded in a wrapping document.

\section{Example of using the epslatex terminal driver}

\label{epslatex}

The epslatex terminal driver allows you to mix the best features of \TeX\

and PostScript. Text elements are typeset by \TeX\, while the graphic

elements are created and positioned in parallel by gnuplot's PostScript

driver. The plot can use either color or grayscale.

The driver produces two different files, one for the eps part of the figure

and one for the \LaTeX{} part. The name of the \LaTeX{} file is taken from the

`set output` command. The name of the eps file is derived by replacing

the file extension (normally ``.tex'') with ``.eps'' instead.

With the epslatex terminal you cannot use ``\verb+\\+'' in a plain

string to denote newline. You can either put each line in a separate

label and specify vertical spacing

manually, or put the entire label in a \verb+\parbox+.

For example, the labels in Figure~\ref{epslatex_test} were

generated with the following commands:

\begin{verbatim}

\end{verbatim}

\boxfigure{htbp}{\fullboxwidth}{

\begin{center}

\input{eg7}

\end{center}

\caption{Interlocking tori demo, drawn using the epslatex driver.}

\label{epslatex_test}

}

\begin{figure}[htbp]

\begin{center}

\input{test}

\end{center}

\caption{Line and point types for the basic latex terminal. Note lack of text rotation.}

\label{testcomp}

\end{figure}

\section{Contact for help}

For general gnuplot questions, you can post to the gnuplot newsgroup

\url{comp.graphics.apps.gnuplot}.

Additional sources of information are listed on the gnuplot homepage

\url{http://www.gnuplot.info}.

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