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                                 Gnuplot FAQ

Contents

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

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.ucc.ie 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: 1.4, dated Date: 99/10/07 09:37:56

0.2 Where do I send comments about this document?

Send comments, suggestions etc via email to the developer newsgroup
info-gnuplot-beta@Dartmouth.EDU and additionally to j.vonhagen@web.de .

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 October 20, 1999. 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.

Gnuplot3.7 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.math-cs.uni.edu/cs/Help/gnuplot/TOC.html contains an online
     tutorial
   * ~http://brian.me.tufts.edu/GnuplotInLaTeX/ contrains infos abount
     gnuplot and LATEX
   * ~http://www.eso.org/ ndevilla/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://mucha.obspm.fr/ grouss/gnuplt/gnuplot.html contient des
     informations dans la langue de Molière: les 1ers pas avec gnuplot,
     malheureusement seulement version 3.5
   * ~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://users.ece.gatech.edu/ schooley/gnuplot.html contains a
     Macintosh version based on 3.6 beta 322

The following sites were said to exist, howevere 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 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.ucc.ie 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 prefered, 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 LATEXterminal 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 Q2.2) 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/ dineo/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 feature is in gnuplot 3.7 when using the set multiplot command.

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

You might try using the LATEXterminal type and putting text like
"\alpha_{3}" into it.

The enhanced option in the postscript terminal is also able to use sub- and
superscripts.

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

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

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 gnuplotdistribution 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 gnuplotrelated 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 gnuplotif at all possible.

5.2 Can I use gnuplotroutines for my own programs?

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

On systems supporting the pipes, you can pipe commands to gnuplotfrom 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 .

5.4 Can I do heavy-duty data processing with gnuplot?

gnuplotalone 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 gnuplotas 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
gnuplot3.7.

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 .

5.5 I have ported gnuplotto 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
gnuplotit 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 gnuplotit is
to be applied against. For the time being (summer 1999) you can also send
the patch to gnuplot@ftp.ucc.ie .

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

Join the gnuplotbeta 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 .

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".

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 blanc 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.

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 removec 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
aplot!

You can call gnuplot by using a short Perl-script like the following:

#!/usr/bin/perl
open GP, "/usr/local/bin/gnuplot";
print GP,"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 thre 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 Jürgen 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 98.1p1
release (March 2nd, 1998)

Copyright © 1993, 1994, 1995, 1996, 1997, Nikos Drakos, Computer Based
Learning Unit, University of Leeds.

The command line arguments were:
latex2html -split 0 -show_section_numbers -html_version 3.2 gnuplot-faq.tex.

The translation was initiated by Juergen von Hagen on 1999-10-20
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