                                  Gnuplot FAQ                                  
                                                                               

Contents

  * 0 Meta - Questions
      + 0.1 Where do I get this document?
      + 0.2 Where do I send comments about this document?
   
  * 1 General Information
      + 1.1 What is gnuplot?
      + 1.2 How did it come about and why is it called gnuplot?
      + 1.3 Does gnuplot have anything to do with the FSF and the GNU project?
      + 1.4 What does gnuplot offer?
      + 1.5 Is gnuplot suitable for batch processing?
      + 1.6 Can I run gnuplot on my computer?
      + 1.7 Legalize it!
      + 1.8 Is gnuplot Y2K compliant?
      + 1.9 Where do I get further information?
   
  * 2 Setting it up
      + 2.1 What is the current version of gnuplot?
      + 2.2 Where can I get gnuplot?
      + 2.3 How do I get gnuplot to compile on my system?
      + 2.4 What documentation is there, and how do I get it?
   
  * 3 Working with it.
      + 3.1 How do I get help?
      + 3.2 How do I print out my graphs?
      + 3.3 How do I include my graphs in <word processor>?
      + 3.4 How do I post-process a gnuplot graph?
      + 3.5 How do I change symbol size, line thickness and the like?
      + 3.6 How do I generate plots in the GIF format?
      + 3.7 Can I animate my graphs?
      + 3.8 How do I plot implicit defined graphs?
   
  * 4 Wanted features
      + 4.1 What's new in gnuplot 3.7?
      + 4.2 Does gnuplot have hidden line removal?
      + 4.3 Does gnuplot support bar-charts/histograms/boxes?
      + 4.4 Does gnuplot support pie charts?
      + 4.5 Does gnuplot quarterly time charts?
      + 4.6 Does gnuplot support multiple y-axes on a single plot?
      + 4.7 Can I put multiple pages on one page?
      + 4.8 Can I put both data files and commands into a single file?
      + 4.9 Can I put Greek letters and super/subscripts into my labels?
      + 4.10 Can I do 1:1 scaling of axes?
      + 4.11 Can I put tic marks for x and y axes into 3d plots?
      + 4.12 Does gnuplot support a driver for <graphics format>?
      + 4.13 Can I put different text sizes into my plots?
      + 4.14 How do I modify gnuplot, and apply 'patches'?
      + 4.15 How do I skip data points?
      + 4.16 How do I plot every nth point?
      + 4.17 How do I plot a vertical line?
      + 4.18 How do I plot data files
      + 4.19 How do I include accentuated characters in Postscript output?
   
  * 5 Miscellaneous
      + 5.1 I've found a bug, what do I do?
      + 5.2 Can I use gnuplot routines for my own programs?
      + 5.3 What extensions have people made to gnuplot? Where can I get them?
      + 5.4 I need an integration, fft, iir-filter,....!
      + 5.5 Can I do heavy-duty data processing with gnuplot? or What is beyond
        gnuplot?
      + 5.6 I have ported gnuplot to another system, or patched it. What do I
        do?
      + 5.7 I want to help in developing the next version of gnuplot. What can
        I do?
      + 5.8 Open questions for inclusion into the FAQ?
   
  * 6 Making life easier
      + 6.1 How do I plot two functions in non-overlapping regions?
      + 6.2 How do I run my data through a filter before plotting?
      + 6.3 How do I make it easier to use gnuplot with LATEX?
      + 6.4 How do I save and restore my settings?
      + 6.5 How do I plot lines (not grids) using splot?
      + 6.6 How do I plot a function f(x,y) which is bounded by other functions
        in the x-y plain?
      + 6.7 How do I get rid of <feature> in a plot?
      + 6.8 How do I call gnuplot from my own programs?
      + 6.9 What if I need h-bar (Planck's constant)?
   
  * 7 Known Problems
      + 7.1 Gnuplot is not plotting any points under X11! How come?
      + 7.2 My isoline data generated by a Fortran program is not handled
        correctly. What can I do?
      + 7.3 Why does gnuplot ignore my very small numbers?
      + 7.4 Gnuplot is plotting nothing when run via gnuplot <filename>! What
        can I do?
      + 7.5 My formulas are giving me nonsense results! What's going on?
      + 7.6 Set output 'filename' isn't outputting everything it should!
      + 7.7 When using the LATEX-terminal, there is an error during the
        LATEX-run!
      + 7.8 The exit command does not work as documented!
      + 7.9 I can't find the demos and example files at the URLs in the
        documentation!
      + 7.10 Calling gnuplot in a pipe or with a gnuplot-script doesn't produce
        a plot!
   
  * 8 Credits

0 Meta - Questions

0.1 Where do I get this document?

This document is posted about once every two weeks to the newsgroups  ~
comp.graphics.apps.gnuplot. Its newest (plaintext) version is available via
anonymous ftp from ftp.gnuplot.info in /pub/gnuplot/faq/gnuplot-faq.txt.

If you have access to the WWW, you can get the newest version of this document
from http://www.ucc.ie/gnuplot/gnuplot-faq.html.

Today's version is version $Revision: 1.3.2.8 $, dated $Date: 2002/12/07 18:33:
30 $

0.2 Where do I send comments about this document?

Send comments, suggestions etc via email to the developer mailing list 
info-gnuplot-beta@Dartmouth.EDU.

1 General Information

1.1 What is gnuplot?

gnuplot is a command-driven interactive function plotting program. It can be
used to plot functions and data points in both two- and three-dimensional plots
in many different formats, and will accommodate many of the needs of today's
scientists for graphic data representation. gnuplot is copyrighted, but freely
distributable; you don't have to pay for it.

This document deals with gnuplot Version 3.7 which is the latest official
release as of December 10, 2002. References to bug-fix versions or (recent)
beta versions are explicitly marked.

1.2 How did it come about and why is it called gnuplot?

The authors of gnuplot are: Thomas Williams, Colin Kelley, Russell Lang, Dave
Kotz, John Campbell, Gershon Elber, Alexander Woo and many others.

The following quote comes from Thomas Williams:

    I was taking a differential equation class and Colin was taking
    Electromagnetics, we both thought it'd be helpful to visualize the
    mathematics behind them. We were both working as sys admin for an EE VLSI
    lab, so we had the graphics terminals and the time to do some coding. The
    posting was better received than we expected, and prompted us to add some,
    albeit lame, support for file data.

    Any reference to GNUplot is incorrect. The real name of the program is
    "gnuplot". You see people use "gnuplot" quite a bit because many of us have
    an aversion to starting a sentence with a lower case letter, even in the
    case of proper nouns and titles. gnuplot is not related to the GNU project
    or the FSF in any but the most peripheral sense. Our software was designed
    completely independently and the name "gnuplot" was actually a compromise.
    I wanted to call it "llamaplot" and Colin wanted to call it "nplot." We
    agreed that "newplot" was acceptable but, we then discovered that there was
    an absolutely ghastly pascal program of that name that the Computer Science
    Dept. occasionally used. I decided that "gnuplot" would make a nice pun and
    after a fashion Colin agreed.

1.3 Does gnuplot have anything to do with the FSF and the GNU project?

Gnuplot is neither written nor maintained by the FSF. It is not covered by the
General Public License, either. It used to be distributed by the FSF, however,
due to licensing issues it is no longer.

Gnuplot is freeware in the sense that you don't have to pay for it. However it
is not freeware in the sense that you would be allowed to distribute a modified
version of your gnuplot freely. Please read and accept the Copyright file in
your distribution.

1.4 What does gnuplot offer?

  * Plotting of two-dimensional functions and data points in many different
    styles (points, lines, error bars)
  * computations in integer, float and complex arithmetic
  * plotting of three-dimensional data points and surfaces in many different
    styles (contour plot, mesh).
  * support for complex arithmetic
  * self - defined functions
  * support for a large number of operating systems, graphics file formats and
    devices
  * extensive on-line help
  * labels for title, axes, data points
  * command line editing and history on most platforms

1.5 Is gnuplot suitable for batch processing?

Yes. You can read in files from the command line, or you can redirect your
standard input to read from a file. Both data and command files can be
generated automatically, from data acquisition programs or whatever else you
use.

1.6 Can I run gnuplot on my computer?

Gnuplot is available for a number of platforms. These are: Unix (X11 and
NeXTSTEP), VAX/VMS, OS/2, MS-DOS, Amiga, MS-Windows, OS-9/68k, Atari ST, BeOS,
and the Macintosh.

Please notify the FAQ-maintainer of any further ports you might be aware of.

You should be able to compile the gnuplot source more or less out of the box on
any reasonable standard (ANSI/ISO C, POSIX) environment.

1.7 Legalize it!

Gnuplot is freeware authored by a collection of volunteers, who cannot make any
legal statement about the compliance or non-compliance of gnuplot or its uses.
There is also no warranty whatsoever. Use at your own risk.

Citing from the README of a mathematical subroutine package by R. Freund:

    For all intent and purpose, any description of what the codes are doing
    should be construed as being a note of what we thought the codes did on our
    machine on a particular Tuesday of last year. If you're really lucky, they
    might do the same for you someday. Then again, do you really feel *that*
    lucky?

1.8 Is gnuplot Y2K compliant?

Gnuplot's compliance depends in part on the compliance of the underlying
operating system and hardware. The only use gnuplot makes of a system- supplied
date is in the "set timestamp" command, which simply echos the date on the
plot. If the underlying OS cannot produce an accurate time string, then the
"set timestamp" command may fail to print the correct date on plots.

In gnuplot 3.5, if the user chooses to use %y in a timestamp format, rather
than %Y, it will print 2-digit rather than 4-digit years. The effects depend on
the importance you place on the timestamps printed on plots.

Gnuplot 3.7 also allows the use of time/date data as variables, but the user
has complete control over the input format of the data and the output format of
the tic labels - the same 2-digit "%y" (interpreted as 1900+) and 4-digit "%Y"
formats are both available. But again, these are user-specifiable, so if there
is a Y2K problem here, it is the responsibility of the user.

Of course, gnuplot is built by executing a makefile, which may well be
date-dependent. So if the operating system has a Y2K problem, the process of
building a new executable of gnuplot may be affected. But that wouldn't be a
problem with gnuplot per se.

IMPORTANT NOTICE

As of gnuplot beta version 3.7.0.9, the interpretation of the "%y" two digit
year specifier was changed in accordance with the recommendations of The Open
Group and all major Unix vendors. When a century is not otherwise specified,
values in the range 69-99 refer to the twentieth century and values in the
range 00-68 refer to the twenty-first century. Be very careful when
interpreting 2-digit year expressions.

1.9 Where do I get further information?

The following sites have more information about gnuplot.

  * http://www.comnets.rwth-aachen.de/doc/gnu/gnuplot37/gnuplot.html an online
    documentation in html-format
  * http://www.usf.uni-osnabrueck.de/ breiter/tools/gnuplot/index.en.html has
    many links to many features and add-ons for gnuplot
  * http://web.cs.uni.edu/Help/gnuplot/ contains an online tutorial
  * http://brian.me.tufts.edu/GnuplotInLaTeX/ contains infos abount gnuplot and
    LATEX
  * http://ndevilla.free.fr/gnuplot/ explains the use of a gnuplot API in ANSI
    C (commonly known as gnuplot_pipes
  * http://ricardo.ecn.wfu.edu/ cottrell/qplot/ on how to plot quarterly time
    data
  * http://monsoon.harvard.edu/ mhagger/download a Python interface for gnuplot
  * ftp.thewrittenword.com in /free/by-package/ contains Solaris, IRIX, HP-UX
    and Digital Unix binaries
  * http://www.sci.muni.cz/ mikulik/gnuplot.html has Petr's famous OS/2 mouse
    support and the pm3d terminal for colour 3d surfaces. Furthermore some more
    links to other sites

Some documentation is available in other languages than English. Those include:

  * http://www.multimania.com/ gersoo/gnuplt/index.html contient des
    informations dans la langue de Molière: les 1ers pas avec gnuplot,
    malheureusement seulement version 3.5. Vous trouverez un cours directement
    en ligne appelleé "1ers pas avec gnuplot". Le cours est aussi disponible en
    Postscript.
  * http://www.al.lu/euler/gnuplot.shtml encore des informations en langue
    française avec possibilité de téléchargement des versions binaires

Here are some more sites, however these are somewhat outdated in carrying still
references to beta versions. If you download software from there you should be
aware that beta versions are not officially endorsed.

  * http://www.cs.dartmouth.edu/gnuplot_info.html slightly outdated site for
    the 3.6 beta version, but also a web-gateway to the users' newsgroup
  * http://members.theglobe.com/gnuplot/ basically same as above.
  * http://homepage.mac.com/gnuplot/ is the new site for a Macintosh port of
    gnuplot

The following sites were said to exist, however they seem to be down right now.

  * http://www.geocities.com/SiliconValley/Foothills/6647/ the copyright
    statement and some binaries contains ads
  * http://www.delorie.com/gnu/docs/gnuplot/gplot_toc.html doesn't work
  * picard.tamu.edu in /pub/gnuplot gives a tutorial
  * http://feff.phys.washington.edu/ ravel/gnuplot has a new mode for the users
    of (X)Emacs

2 Setting it up

2.1 What is the current version of gnuplot?

The current version of gnuplot is 3.7, which has many improvements over 3.5.
3.6 was never released to avoid confusions with the beta versions.


2.2 Where can I get gnuplot?

The best place is definitly http://www.gnuplot.info. From there you find
various pointers to other sites.

The source distribution ("gnuplot-3.7.tar.gz" or a similar name) is available
from the official distribution site and its mirrors.

The main server is ftp.gnuplot.info in /pub/gnuplot/. This server is mirrored
by several others, among those are

  * mirror.aarnet.edu.au in /pub/gnuplot/
  * ftp.dartmouth.edu in /pub/gnuplot/
  * ftp.irisa.fr in /pub/gnuplot/
  * ftp.gnuplot.vt.edu in /pub/gnuplot/

You can also have a look at the following WWW-pages which provide a source to
obtain gnuplot:

  * http://members.theglobe.com/gnuplot/
  * http://www.geocities.com/SiliconValley/Foothills/6647/
  * http://mirror.aarnet.edu.au/pub/gnuplot/

The current version for the Macintosh is 2.04b, based on gnuplot 3.5
pre3.6beta338, and is available from

  * http://users.ece.gatech.edu/ schooley/.

Unfortunately, this version does not seem to be maintained anymore.

Source and binary distributions for the Amiga are available on Aminet 
ftp.wustl.edu in  aminet/ and its mirrors, for example ftp.uni-kl.de,
oes.orst.edu or ftp.luth.se.

MS-DOS and MS-Windows binaries are available from the above servers and are
called gp37dos.zip, gp37dj.zip, gp37w16.zip, gp37mgw.zip, gnuplot3.7cyg.zip.

OS/2 binaries are called gp37os2.zip.

An X11 Window System front-end is available at http://www.flash.net/ dmishee/
xgfe/xgfe.html.

The NeXTSTEP front end can be found at next-ftp.peak.org in /pub/next/binaries/
plotting/Gnuplot1.2_bin.tar.Z.

A version for OS-9/68K can be found at cabrales.cs.wisc.edu in /pub/OSK/
GRAPHICS/gnuplot32x.tar.Z; it includes both an X-Window Systems and a non -
X-Window Systems version.

Versions for the Atari ST and TT, which include some GEM windowing support, are
available from ftp.uni-kl.de in /pub/atari/graphics/, as gplt35st.zip and
gplt35tt.zip. They work best under MiNT.

Executable files, plus documentation in Japanese, exist for the X680x0 on 
ftp.csis.oita-u.ac.jp in /pub/x68k/fj.binaries.x68000/vol2.

It is a good idea to look for a nearby ftp site when downloading things. You
can use archie for this. See if an archie client is installed at your system
(by simply typing archie at the command prompt), or send mail to 
archie@sura.net with the word 'help' in both the subject line and the body of
the mail. However, be aware that the version you find at a near ftp site may
well be out of date; check the last modification date and the number of bytes
against the newest release at one of the official servers.

If you can't locate a working archie server, you can use other web-based search
engines for searching for gnuplot. One of these would be Lycos at http://
ftpsearch.lycos.com/.

As of June 1999, the gnuplot distribution is also mirrored at the Comprehensive
TeX Archive Network (CTAN) in the graphics/gnuplot directory. See

  * http://www.ctan.org/.

Bug fixes can also be found at gnuplot distribution sites in the patches
directory.

2.3 How do I get gnuplot to compile on my system?

As you would any other installation. Read the files README.1ST and README.

For Unix, use configure and make. For DOS, if you are using bash and DJGPP, you
can just run djconfig.sh. For other platforms, copy the relevant makefile from
config/ to src, change to src and run make.

2.4 What documentation is there, and how do I get it?

The documentation is included in the source distribution. Look at the docs
subdirectory, where you'll find

  * a Unix man page, which says how to start gnuplot
  * a help file, which also can be printed as a manual
  * a tutorial on using gnuplot with LATEX
  * a quick reference summary sheet for TEXonly

PostScript copies of the documentation can be ftp'd from ftp.dartmouth.edu in /
pub/gnuplot, as manual.ps.Z and tutorial.ps.Z

The documentation is built during the installation if you have LATEX installed
on your system, look in the directories docs and tutorial.

Documentation about gnuplot is available in the most common formats at the
gnuplot distribution sites in the files gpdoc.zip and gpdoc2.zip.

3 Working with it.

3.1 How do I get help?

Read this document.

Give the 'help' command at the initial prompt. After that, keep looking through
the keywords. Good starting points are 'plot' and 'set'.

Read the manual, if you have it.

Look through the demo subdirectory; it should give you some ideas.

Ask your colleagues, the system administrator or the person who set up gnuplot.

If all these fail, please upgrade to the newest version of gnuplot or urge your
system-administrator to do so. Then post a question to ~
comp.graphics.apps.gnuplot or send mail to the gatewayed mailing list 
info-gnuplot@dartmouth.edu. Do not forget to cite the version number and the
operating system. If you want to subscribe to the mailing list, send a mail to 
majordomo@dartmouth.edu with the body of the message being 'subscribe
info-gnuplot'. Please don't do this if you can get  ~comp.graphics.apps.gnuplot
directly. If you post a question there, it is considered good form to solicit
e-mail replies and post a summary.

3.2 How do I print out my graphs?

The kind of output produced is determined by the 'set terminal' command; for
example, 'set terminal postscript' will produce the graph in PostScript format.
Output can be redirected using the 'set output' command.

As an example, the following prints out a graph of sin(x) on a Unix machine
running the X-Window System.

gnuplot> plot [-6:6] sin(x)
gnuplot> set terminal postscript
Terminal type set to 'postscript'
Options are 'landscape monochrome "Courier" 14'
gnuplot> set output "sin.ps"
gnuplot> replot
gnuplot> set output              # set output back to default
gnuplot> set terminal x11        # ditto for terminal type
gnuplot> ! lp -ops sin.ps        # print PS File (site dependent)
request id is lprint-3433 (standard input)
lp: printed file sin.ps on fg20.rz.uni-karlsruhe.de (5068 Byte)
!
gnuplot>

In Microschrott Windows you click in the upper left corner of the graph window
and print directly from there.

3.3 How do I include my graphs in <word processor>?

Basically, you save your plot to a file in a format your word processor can
understand (using "set term" and "set output", see above), and then you read in
the plot from your word processor. Vector formats should be preferred, as you
can scale your graph later to the right size.

Details depend on the kind of word processor you use; use "set term" to get a
list of available file formats.

Many word processors can use Encapsulated PostScript for graphs. This can be
generated by the "set terminal postscript eps" command. Most MS-DOS word
processors understand HPGL (terminal type hpgl).

With TeX, it depends on what you use to print your dvi files. If you use dvips
or dvi2ps, you can use Encapsulated PostScript. For emTeX (popular for MS-DOSns
OS/2), you can use emTeX, otherwise use the LATEX terminal type, which
generates a picture environment.

If nothing else helps, try using the pgm or ppm format and converting it to a
bitmap format your favourite word processor can understand. An invaluable tool
for this is Jef Poskanzer's PBMPLUS package.

The PBMPLUS package is available in the contrib distribution for the X-Window
System. The original site for this is ftp.x.org in /contrib/. There are many
mirrors, e.g. ftp.tu-darmstadt.de in /pub/X11/contrib/ or . sunsite.unc.edu in
/pub/X11/contrib/.

The most recent release of pbm by the author is dated December 91 and is called
pbmplus10dec91.tar.Z.

There is new version including lots of patches from the net that is not
maintained by the author called netpbm, with the newest version called
netpbm-1mar1994.tar.gz.

Check archie (see Q[*] ) for an archive site near you.

For Microso$t Windows and MacOS you can use the clip board to copy your graph
and paste it into your favourite Windows or MacOS word processor.

3.4 How do I post-process a gnuplot graph?

This depends on the terminal type you use.

You can use the terminal type fig (you may need to recompile gnuplot to enable
this terminal type, by putting #define FIG into <term.h>), and use the xfig
drawing program to edit the plot afterwards. You can obtain the xfig program
from its web site http://www.xfig.org/. More information about the text-format
used for fig can be found in the fig-package.

You may use the tgif terminal, which creates output suitable for reading within
tgif (http://bourbon.cs.umd.edu:8001/tgif/), an interactive 2-D drawing tool
under X11.

Both tgif and xfig can also be obtained from the X Window contrib distribution
(see Q3.3).

Pstoedit can convert Postscript into a wide variety of formats. Pstoedit is
available a http://www.geocities.com/SiliconValley/Nework/1958/pstoedit/.

Gimp may be able to post-process pixel graphics generated with gnuplot.

In general, you should use a vector graphics program to post-process vector
graphic formats, and pixel based programs for pixel graphics.

3.5 How do I change symbol size, line thickness and the like?

Again, this depends on the terminal type. For PostScript, you can edit the
generated PostScript file. An overview of what means what in the PostScript
files gnuplot generates can be found at picard.tamu.edu in /pub/gnuplot/ as
gs-ps.doc. A general introduction to PostScript can be found at 
unix.hensa.ac.uk in /pub/misc/ukc.reports/comp.sci/reports/ as 11-92.ps.Z.

3.6 How do I generate plots in the GIF format?

If gnuplot was compiled with the external GD library, there is a gif terminal.

As of version 1.6, gd library dropped support for gif in favour of the superior
png format. For those who absolutely need gif support in gnuplot, we are
providing older versions of gd library at the gnuplot distribution sites which
are free of Unisys patented code. Please read also the file README a the
ftp-sites.

3.7 Can I animate my graphs?

First have a look at animate.dem in the demo directory of gnuplot. Basically,
animated graphs are a sequence of plots in a suitable format.

Then have a look at the tool whirlgif 3.04, available at http://www.danbbs.dk/
 dino/whirlgif. It reads run-length encoded gifs and packs them into a minimal
animation. On the web-pages you will find a manual and an example.

You can also write a small script to get gnuplot to output a family of GIF
files, then have it execute some animator such as gifsicle: http://http://
www.lcdf.org/ eddietwo/gifsicle or gifmerge http://http://the-labs.com/GIFMerge

mpeg_encode will encode a sequence of images into the mpeg-format.

3.8 How do I plot implicit defined graphs?

Implicit graphs or curves cannot be plotted directly in gnuplot. However there
is a workaround.
gnuplot> # as example. Place your definition in the following line
gnuplot> f(x,y) = y - x**2 / tan(y)
gnuplot> set contour base
gnuplot> set cntrparam levels discrete 0.0
gnuplot> set nosurface
gnuplot> set term table
gnuplot> set out 'curve.dat'
gnuplot> splot f(x,y)
gnuplot> set out
gnuplot> set term {your usual terminal for interactive work}
gnuplot> plot 'curve.dat' w l
The trick is to draw the single contour line z=0 of the surface z=f(x,y), and
store the resulting contour curve to a gnuplot datafile.

4 Wanted features

4.1 What's new in gnuplot 3.7?

Too many things to be named here. Please refer to the NEWS file in the source
distribution.

4.2 Does gnuplot have hidden line removal?

Version 3.7 supports hidden line removal on all platforms; use the command set
hidden3d.

The 16-bit binaries of gnuplot support the hidden line removal only partially
as the hidden-line algorithm may hit the 640k memory limit.

4.3 Does gnuplot support bar-charts/histograms/boxes?

Use the style "with boxes" for bar charts. To get filled boxes, you can try a
modification by Steve Cumming and jturk, available via ftp from the contrib
directory ftp.ucc.ie in /pub/gnuplot/contrib/gpl37fboxpatch.tar.gz.

Bernhard Reiter wrote an AWK script to post-process the fig-terminal output.
Please have a look at http://www.usf.uni-osnabrueck.de/ breiter/tools/gnuplot/
barcharts.en.html.

4.4 Does gnuplot support pie charts?

It's not possible in gnuplot, but have a look at http://
www.usf.uni-osnabrueck.de/ breiter/tools/piechart/piecharts.en.html

4.5 Does gnuplot quarterly time charts?

It's not possible in gnuplot, but have a look at http://ricardo.ecn.wfu.edu/
 cottrell/qplot. The corresponding file qplot.zip can be obtained from the
contrib directory on any gnuplot server.

4.6 Does gnuplot support multiple y-axes on a single plot?

Yes. You can have 2 x- and 2 y-axes per plot. See "plot".

4.7 Can I put multiple pages on one page?

Yes. "set multiplot"

If you use the postscript terminal and plot one graph per page you can use the
program mpage (http://www.mesa.nl/pub/mpage) to print multiple logical pages
per physical page. A similar program is the psnup program in the psutils
package. This package is available at any CTAN mirror.

4.8 Can I put both data files and commands into a single file?

This is possible by the new plot "-" possibility. The plot "-" command allows
to read the data to be plot from standard input or the current batch job.

gnuplot> plot "-"
1 1
2 4
3 9
<CTRL-D>

4.9 Can I put Greek letters and super/subscripts into my labels?

You might try using the LATEX terminal type and putting text like "\\alpha_{3}"
or '\alpha_{3}' into it.

The enhanced option in the postscript terminal is also able to use sub- and
superscripts. It also allows to use Greek letters and symbols via symbol fonts.

If you include your gnuplot-graphs into a LATEX document you can use the
LATEX-package psfrag to typeset any characters into your graphs.

One more possibility is to use the MetaPost terminal. It supports TEX syntax
and is converted onto encapsulated PostScript by mpost.

4.10 Can I do 1:1 scaling of axes?

Use "set size square".

4.11 Can I put tic marks for x and y axes into 3d plots?

Use the "with boxes" option.

4.12 Does gnuplot support a driver for <graphics format>?

To see a list of the available graphic drivers for your installation of
gnuplot, type "set term".

Some graphics drivers are included in the normal distribution, but are
uncommented by default. If you want to use them, you'll have to change gnuplot/
term.h, and recompile.

4.13 Can I put different text sizes into my plots?

Some terminals, like the postscript terminal can, others can't. Look at the
help for the different terminals.

4.14 How do I modify gnuplot, and apply 'patches'?

For this, you will need to recompile gnuplot.

Modifications people make are either done by replacing files, such as terminal
drivers, or by 'patching'. If a file is a replacement, it will probably tell
you in its README or in the lines at the beginning.

To patch a file, you need Larry Wall's patch utility. On many UNIX systems, it
is already installed; do a man patch to check. If it isn't, you'll have to get
it; it can be found wherever GNU software is archived.

4.15 How do I skip data points?

By specifying ? as a data value, as in
        1 2
        2 3
        3 ?
        4 5

4.16 How do I plot every nth point?

This can be specified with the various options for the command "plot".

4.17 How do I plot a vertical line?

Depending on context, the main methods are:

  * set arrow .... .... nohead where you have to compute explicitly the start
    and the end of the arrow.
  * generate (inlined) datapoints and plot them
  * switch to parametric mode

4.18 How do I plot data files

4.19 How do I include accentuated characters in Postscript output?

To obtain accentuated characters like ü or n into postscript plots you should
use the postscript character codes together with the appropriate encoding
option. See the following example:

gnuplot> set encoding iso_8859_1
gnuplot> set title "M\374nchner Bierverbrauch \374ber die Jahre"
gnuplot> plot "bier.dat" u 1:2

5 Miscellaneous

5.1 I've found a bug, what do I do?

First, try to see whether it actually is a bug, or whether it is a feature
which may be turned off by some obscure set-command.

Next, see whether you have an old version of gnuplot; if you do, chances are
the bug has been fixed in a newer release.

Fixes for bugs reported since the release of the current version are held in
the patches directory at gnuplot distribution sites. Before submitting a bug
report, please check whether the bug in question has already been fixed.

If, after checking these things, you still are convinced that there is a bug,
proceed as follows. If you have a fairly general sort of bug report, posting
to ~comp.graphics.apps.gnuplot is probably the way to go. If you have
investigated a problem in detail, especially if you have a context or unified
diff that fixes the problem, please e-email a report to 
bug-gnuplot@dartmouth.edu.

The bug-gnuplot list is for reporting and collecting bug fixes, the  ~
comp.graphics.apps.gnuplot newsgroup will be more help for finding work arounds
or actually solving gnuplot related problems. If you do send in a bug report,
be sure and include the version of gnuplot (including patchlevel) as shown by
the command "show version long", terminal driver, operating system, an exact
description of the bug and input which can reproduce the bug. Failure to
indicate these details can render a solution to your problem almost impossible.
Also, any context diffs should be referenced against the latest official
version of gnuplot if at all possible.

5.2 Can I use gnuplot routines for my own programs?

Yes. John Campbell jdc@nauvax.ucc.nau.edu has written gplotlib, a version of
gnuplot as C subroutines callable from a C program. This is available as
gplotlib.tar.gz at ftp.nau.edu in /pub/gplotlib.tar.gz. This library has been
updated to be compatible with version 3.5.

On systems supporting the pipes, you can pipe commands to gnuplot from other
programs.

5.3 What extensions have people made to gnuplot? Where can I get them?

Extensions are available from ftp.ucc.ie in /pub/gnuplot/contrib/

Some extensions available:

  * barchart_via_fig: awk scripts to produce barcharts with filled boxes.
  * date-errorbar: allows dates in the hi/lo fields for errorbars.
  * gp37os2-mouse: OS/2 binaries with mouse support (feature included in
    current beta versions).
  * perltk: A perl/tk canvas widget.
  * polyg.patch: Implements a polygon plotting style.
  * xgfe: graphical front end using the Qt widgets available at http://
    lnc.usc.edu/docs/xgfe/xgfe.html.
  * Gnuplot.py: A python package to create graphs from within python. More
    information at http://monsoon.harvard.edu/ mhagger/Gnuplot/Gnuplot.html.

5.4 I need an integration, fft, iir-filter,....!

Gnuplot has been and is a plotting program, no data processing or mathematical
program suite. Therefore gnuplot can't do that. Look into the demo
"bivariat.dem" for a basic implementation of an integration.

For more sophisticated data-processing read the next section.

5.5 Can I do heavy-duty data processing with gnuplot? or What is beyond
gnuplot?

gnuplot alone is not suited very well for this. One thing you might try is
fudgit, an interactive multi-purpose fitting program written by Martin-D.
Lacasse (isaac@frodo.physics.mcgill.ca). It can use gnuplot as its graphics
back end and is available from ftp.physics.mcgill.ca in /pub/Fudgit/
fudgit_2.33.tar.Z and from the main Linux server, tsx-11.mit.edu and its
numerous mirrors around the world as /pub/linux/sources/usr.bin/
fudgit-2.33.tar.z. Versions are available for AIX, Data General, HP-UX, IRIX 4,
Linux, NeXT, Sun3, Sun4, Ultrix, OS/2 and MS-DOS. The MS-DOS version is
available on simtel20 mirrors (simtel20 itself has closed down) in the "math"
subdirectory as fudg_231.zip.

Carsten Grammes has written a fitting program which has been merged into
gnuplot 3.7.

Michael Courtney has written a program called lsqrft, which uses the
Levenberg-Marquardt - Algorithm for fitting data to a function. It is available
from hobbes.nmsu.edu in /pub/os2/apps/analysis/lsqrft15.zip; sources, which
should compile on Unix, and executables for MS-DOS and OS/2 are available.
There is an interface to the OS/2 presentation manager.

You might also want to look at the applications developed by the Software Tools
Group (STG) at the National Center for Supercomputing Applications. Ftp to
ftp.ncsa.uiuc.edu and get the file README.BROCHURE for more information.

You can also try pgperl, an integration of the PGPLOT plotting package with
Perl 5. Information can be found at http://www.ast.cam.ac.uk/AAO/local/www/kgb/
pgperl, the source is available from ftp.ast.cam.ac.uk in /pub/kgb/pgperl/ or 
linux.nrao.edu in /pub/packages/pgperl/.

Another possibility is Octave. To quote from its README: Octave is a high-level
language, primarily intended for numerical computations. It provides a
convenient command line interface for solving linear and nonlinear problems
numerically. The latest released version of Octave is always available from 
http://www.che.wisc.edu/octave/ and via anonymous ftp from bevo.che.wisc.edu in
/pub/octave. Octave is licensed under GPL (see http://www.gnu.org/copyleft/
gpl.html). By the way, octave uses gnuplot as its plotting engine, so you get a
data-processing program on top of gnuplot.

Finally, there is scilab at http://www-rocq.inria.fr/scilab/ doing about the
same as matlab. It is free but copyrighted software.

5.6 I have ported gnuplot to another system, or patched it. What do I do?

If your patch is small, mail it to info-gnuplot-beta@dartmouth.edu, with a
thorough description of what the patch is supposed to do, which version of
gnuplot it is relative to, etc. Also, you can send notification of the patch to
the FAQ maintainer, if you want a mention. Please don't send the patch itself
to me.

If your modifications are extensive (such as a port to another system), place
them on a web/ftp site for download. There is currently no possibility to
upload patches. Send a note to info-gnuplot-beta@dartmouth.edu on where to find
the patch, what it is supposed to do, which version of gnuplot it is to be
applied against. For the time being (summer 1999) you can also send the patch
to gnuplot@ftp.ucc.ie.

5.7 I want to help in developing the next version of gnuplot. What can I do?

Join the gnuplot beta test mailing list by sending a mail containing the line
subscribe info-gnuplot-beta in the body (not the subject) of the mail to 
Majordomo@Dartmouth.EDU.

Also check with http://sourceforge.net/projects/gnuplot about latest source for
beta releases for development.

5.8 Open questions for inclusion into the FAQ?

info-gnuplot-beta@Dartmouth.EDU.

Please submit your questions (along with the answer) to 
info-gnuplot-beta@Dartmouth.EDU.

6 Making life easier

6.1 How do I plot two functions in non-overlapping regions?

Use a parametric plot. An example:
gnuplot> set parametric
gnuplot> a=1
gnuplot> b=3
gnuplot> c=2
gnuplot> d=4
gnuplot> x1(t) = a+(b-a)*t
gnuplot> x2(t) = c+(d-c)*t
gnuplot> f1(x) = sin(x)
gnuplot> f2(x) = x**2/8
gnuplot> plot [t=0:1] x1(t),f1(x1(t)) title "f1", x2(t), f2(x2(t)) title "f2"

You can also use gnuplot's ability to ignore mathematically undefined
expressions: the expression 1/0 is silently ignored, thus a construction like
gnuplot> set xran [-10:10]
gnuplot> plot (abs(x)>0.5?1/0: x**2)
plots a quadratic function only for |x| < 0.5.

6.2 How do I run my data through a filter before plotting?

If your system supports the popen() function, as Unix does, you should be able
to run the output through another process, for example a short awk program,
such as

gnuplot> plot "< awk ' { print $1, $3/$2 } ' file.in"

The plot command is very powerful and is able to do some arithmetic on
datafiles. See "help plot".

6.3 How do I make it easier to use gnuplot with LATEX?

There is a set of LATEX macros and shell scripts that are meant to make your
life easier when using gnuplot with LATEX. This package can be found on 
ftp.dartmouth.edu in pub/gnuplot/latex.shar, by David Kotz. For example, the
program "plotskel" can turn a gnuplot-output file plot.tex into a skeleton file
skel.tex, that has the same size as the original plot but contains no graph.
With the right macros, the skeleton can be used for preliminary LATEX passes,
reserving the full graph for later passes, saving tremendous amounts of time.

6.4 How do I save and restore my settings?

Use the "save" and "load" commands for this; see "help save" and "help load"
for details.

6.5 How do I plot lines (not grids) using splot?

If the data in a data file for splot is arranged in such a way that each one
has the same number of data points (using blank lines as delimiters, as usual),
splot will plot the data with a grid. If you want to plot just lines, use a
different number of data entries (you can do this by doubling the last data
point, for example). Don't forget to set parametric mode, of course.

6.6 How do I plot a function f(x,y) which is bounded by other functions in the
x-y plain?

An example:
gnuplot> f(x,y) = x**2 + y **2
gnuplot> x(u) = 3*u
gnuplot> yu(x) = x**2
gnuplot> yl(x) = -x**2
gnuplot> set parametric
gnuplot> set cont
gnuplot> splot [0:1] [0:1] u,yl(x(u))+(yu(x(u)) - yl(x(u)))*v,\
> f(x(u), (yu(x(u)) - yl(x(u)))*v)

6.7 How do I get rid of <feature> in a plot?

Usually, there is a set command to do this; do a gnuplot> ?set no for a short
overview.

6.8 How do I call gnuplot from my own programs?

There's a code which works for a UNIX system, using (efficient) named pipes. On
M$ Windows platforms, due to the lacking standard input of GUI programs, you
need to use the C-code pgnuplot written by Hans-Bernhard Broeker 
broeker@physik.rwth-aachen.de. You can obtain this file on a ftp-server
carrying the source for gnuplot.

6.9 What if I need h-bar (Planck's constant)?

There is no predefined variable like pi. However to put h-bar as a character
into the label, you must use the PostScript terminal. You can play around with
constructs like @{/=56 -} {/=24 h} or {/=8 @{/Symbol=24 -} _{/=14 h}} In the
latter, the "-" (a long one in /Symbol) is non-spacing and 24-pt. The 14-pt "h"
is offset by an 8-pt space (which is the space preceding the "_") but smaller,
since it's written as a subscript. But these don't look too much like the hbar
we're used to, since the bar is horizontal instead of sloped. I don't see a way
to get that. I tried using an accent (
264 in isoLatin encoding), but I haven't found a way to scale and position the
pieces correctly.

One more possibility would be {/=14 @^{/Symbol=10 -}{/=14 h}}.

(This is a hint by Richard Crawford).

7 Known Problems

7.1 Gnuplot is not plotting any points under X11! How come?

On VMS, you need to make several symbols:

        $ gnuplot_x11 :== $disk:[directory]gnuplot_x11
        $ gnuplot :== $disk:[directory]gnuplot.exe
        $ def/job GNUPLOT$HELP disk:[directory]gnuplot.hlb

Then run gnuplot from your command line, and use "set term x11".

If you run gnuplot on Unix systems, be sure that the newest gnuplot_x11 is the
first in your search path.

7.2 My isoline data generated by a Fortran program is not handled correctly.
What can I do?

Update to the newest gnuplot. Gnuplot 3.7 is able to read Fortran-style files
where a blank line can contain more than a linefeed.

7.3 Why does gnuplot ignore my very small numbers?

Gnuplot treats all numbers less than 1e-08 as zero, by default. Thus, if you
are trying to plot a collection of very small numbers, they may be plotted as
zero. Worse, if you're plotting on a log scale, they will be off scale. Or, if
the whole set of numbers is "zero", your range may be considered empty:

gnuplot> plot 'test1'
Warning: empty y range [4.047e-19:3e-11], adjusting to [-1:1]
gnuplot> set yrange [4e-19:3e-11]
gnuplot> plot 'test1'
              ^
y range is less than `zero`

The solution is to change gnuplot's idea of "zero":
gnuplot> set zero 1e-20

For more information, "help set zero"

7.4 Gnuplot is plotting nothing when run via gnuplot <filename>! What can I do?

Put a pause -1 after the plot command in the file. On an X-Window System
system, you can also use the -persist option, the X11 window is then not
closed. Close the X11 window by typing "q" when the focus is on it.

7.5 My formulas are giving me nonsense results! What's going on?

Gnuplot does integer, and not floating point, arithmetic on integer
expressions. For example, the expression 1/3 evaluates to zero. If you want
floating point expressions, supply trailing dots for your floating point
numbers. Example:

gnuplot> print 1/3
                0
gnuplot> print 1./3.
                0.333333

This way of evaluating integer expressions is shared by both C and Fortran.

7.6 Set output 'filename' isn't outputting everything it should!

You need to flush the output with a closing 'set output'.

7.7 When using the LATEX-terminal, there is an error during the LATEX-run!

Please upgrade to gnuplot 3.7. Some versions of its beta-release had a problem
in the LATEX-terminal.

The LATEX2$\epsilon$ -core does no longer include the commands "
Diamond" and "
Box"; they are included in the latexsym package, which is part of the base
distribution and thus part of any LaTeX implementation. Please do not forget to
use this package.

7.8 The exit command does not work as documented!

This is a known bug and is fixed in the latest release. If you need the feature
please upgrade to the latest release.

7.9 I can't find the demos and example files at the URLs in the documentation!

The examples have been removed from the NASA site. You can find the examples
now at http://www.gnuplot.vt.edu/gnuplot/gpdocs. There you will find both PNG
and GIF versions of the demo plots. There are some licensing problems with GIF
images, so you should probably prefer the PNG ones. They also have the
advantage to be much smaller in size.

7.10 Calling gnuplot in a pipe or with a gnuplot-script doesn't produce a plot!

You can call gnuplot by using a short Perl-script like the following:
#!/usr/local/bin/perl -w
open (GP, "|/usr/local/bin/gnuplot -persist") or die "no gnuplot";
# force buffer to flush after each write
use FileHandle;
GP->autoflush(1);
print GP,"set term x11;plot '/tmp/data.dat' with lines\n";
close GP

Gnuplot closes its plot window on exit. The close GP command is executed, and
the plot window is closed even before you have a chance to look at it.

There are three solutions to this: first, use the pause -1 command in gnuplot
before closing the pipe. Second, close the pipe only if you are sure that you
don't need gnuplot and its plot window anymore. Last, you can use the command
line option -persist: this option leaves the X-Window System plot window open.

8 Credits

Gnuplot 3.7's main contributors are (in alphabetical order) Hans-Bernhard
Broeker, John Campbell, Robert Cunningham, David Denholm, Gershon Elber, Roger
Fearick, Carsten Grammes, Lucas Hart, Lars Hecking, Thomas Koenig, David Kotz,
Ed Kubaitis, Russell Lang, Alexander Lehmann, Alexander Mai, Carsten Steger,
Tom Tkacik, Jos Van der Woude, James R. Van Zandt, and Alex Woo.

This list was initially compiled by John Fletcher with contributions from
Russell Lang, John Campbell, David Kotz, Rob Cunningham, Daniel Lewart and Alex
Woo. Reworked by Thomas Koenig from a draft by Alex Woo, with corrections and
additions from Alex Woo, John Campbell, Russell Lang, David Kotz and many
corrections from Daniel Lewart. Again reworked for gnuplot 3.7 by Alexander Mai
and Juergen v.Hagen with corrections by Lars Hecking, Hans-Bernhard Broecker
and other people.

About this document ...

Gnuplot FAQ

This document was generated using the LaTeX2HTML translator Version 2002-2-1
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University of Leeds.
Copyright © 1997, 1998, 1999, Ross Moore, Mathematics Department, Macquarie
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The command line arguments were:
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The translation was initiated by Lars Hecking on 2002-12-10
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