Gnuplot Examples

To use grnuplot, type gnuplot from the UNIX prompt.

Gnuplot can be run interactively, or from script files. Script files are simply ascii files that have commands written out just as you would enter them interactively. You can run a script two ways:

Type load "scriptname" from within gnuplot.
Or, from UNIX, run gnuplot by typing gnuplot scriptname. In this method, gnuplot will exit when your script is finished, so you may want to include PAUSE -1 "Hit any key to continue" as your last line.

Usually, I test out plotting features interactively (using the help command as needed), and put the commands to generate a plot in a script file so that I can reproduce the graph at a later time. (Having a gnuplot script is great when you are debugging computational programs. You can quickly plot your output files to see if they look reasonable.)

Now for some examples. Note that lines begining with # are comments.

Making an energy plot

Suppose you want to plot the file d1.dat.
Try the following.

#set terminal postfile (These commented lines would be used to ) #set output "d1_plot.ps" (generate a postscript file. ) set title "Energy vs. Time for Sample Data" set xlabel "Time" set ylabel "Energy" plot "d1.dat" with lines pause -1 "Hit any key to continue"

This example uses the default X11 window for output. It sets the name of the plot title. Then it set the names of the x-axis and y-axis to Time and Energy (default would be X and Y). The plot command is really the key line. It plots data from a file, using column 1 and 2 as the default x and y values. The limits are set automatically, and data points are connected with lines. Some variations on the plot command are:

Plot a function. To plot a function instead of a data file, try
plot sin(x) with lines
Plot in a specified range. To plot a data set in the range 0 < x < 10 and 0.2 < y < 0.6, try
plot [0,10] [0.2,0.6] "d1.dat" with lines
Plot with points. To plot with points, or to plot with lines and points, use the folloing forms
plot "d1.dat" with points
plot "d1.dat" with linespoints
Plot different columns of datafile. For example, to take x from column 4 and y from column 2,
plot "data.dat" using 4:2 with lines
Plot several functions at once. To plot d1.dat against the line y(x)=exp(-x), try
plot "d1.dat" with lines, exp(x) with lines
Change the Plot Title. To change the name that appears in the 'key' in the corner of the plot, try
plot "d1.dat" title 'Sample Data' with lines or, if you don't like the key, try
plot "d1.dat" notitle with lines

There are may other variations on the plot command, type


help plot

from more information.

Email your questions/corrections/comments

That's all for now. Please let me know if this is useful. If you have any questions that you want answered here, email me at shumway@uiuc.edu. Also, if you have any gnuplot tricks or techniques you would like to post here, let me know and I'll put them on.

Back to Phys498a Home Page

Last updated January 23rd. shumway@uiuc.edu