Gnuplot + LaTeX:  The Ultimate Plotting Experience

Plotting graphs is an important activity for most of our analysis work. Usually we have a function, say y = f(x) , and a sample of (x,y) pairs. In order to analyze the behavior of the function, we represent the x and its corresponding y values as a graph. We draw a horizontal x-axis and a vertical y-axis. In the graph, we represent each (x,y) pair as a dot or a cross in the x-y plane. Instead of points, we can connect the points with lines or can draw vertical bars (histograms) corresponding to each y value to get more meaningful interpretation of the function. This post is intended to provide information on generating extreme quality graphs using two of the important tools, Gnuplot and LaTeX.

For the remaining of this post, I assume that you have a basic knowledge of Gnuplot and LaTeX. For plotting using this method, we need to have TikZ and LuaTeX libraries installed. Use the following command (in GNU Debian/Ubuntu systems) if your system does not have them.

$ sudo apt-get install gnuplot latexmk pgf preview-latex* texlive-fonts-recommended luatex texlive-pictures texlive-latex-extra

Assume that we have a text file data.txt with input data (the (x,y) pairs) for plotting. For example, you have the speed of a car and a bus at certain time instants. A sample file is as follows.

Time Car Bus
1 10 35
2 45 20
3 30 40
4 25 10
5 60 55

As the next step, write the Gnuplot script for plotting the graph. The following is a sample code, saved as plot.gp.

# Enabling the terminal in LaTeX TikZ mode
set term tikz standalone color solid
# Enabling the dashed line option
set termoption dash
# Setting output file name (Here output is a LaTeX file)
set output 'figure.tex'
# Set title
set title 'Speed Vs Time'
# Set labels for x and y axes
set xlabel 'Time (in minutes)'
set ylabel 'Speed (km/hr)'
# Set the legend
set key horiz top left Left box spacing 2 sample 2
# Plot the graph
plot 'data.txt' u 1:2 w lp lt 1 pt 5 lc rgb 'dark-blue' t columnheader,\
'data.txt' u 1:3 w lp lt 2 pt 7 lc rgb 'dark-green' t columnheader

Execute the Gnuplot code plot.gp using the following command.

$ gnuplot plot.gp

Execution creates a file figure.tex with the TikZ script for drawing the graph. TikZ is used to draw high quality figures in LaTeX (See TeXample). Thanks to Gnuplot's support for TikZ terminal, which allows us to generate a tex file, with scripts to draw the graph, instead of normal image formats such as jpeg or png. As the final step, we need to compile the file figure.tex with pdflatex.

$ pdflatex figure.tex

A file figure.pdf will be generated with the graph. There hardly exist tools to create graphs of higher quality similar to Gnuplot + LaTeX. Since the graph is created using LaTeX, the default font will be the same as the default font provided by LaTeX. Also, LaTeX allows to import figures with .pdf extension using \includegraphics{} command. Presence of such figures improves the effective quality of technical papers.

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Send me suggestions or corrections if any.