(PDF ファイル: faq-1.15.pdf)

Gnuplot FAQ

This document deals with gnuplot version 4.0 which is the latest official release as of April 2004.
Its version is $Revision: 1.15 $, dated $Date: 2004/04/14 13:18:59 $.


0 Meta - Questions

0.1 Where do I get this document?

The newest version of this document is on the web at http://www.gnuplot.info/faq/.

This document was/is posted sometimes to the newsgroups  ~comp.graphics.apps.gnuplot.

0.2 Where do I send comments about this document?

Send comments, suggestions etc via email to the developer mailing list gnuplot-beta@lists.sourceforge.net. Please contribute your suggestions with respect to the file faq.tex available from http://cvs.sourceforge.net/viewcvs.py/gnuplot/faq/.

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. It is designed primarily for the visual display of scientific data. gnuplot is copyrighted, but freely distributable; you don't have to pay for it.

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 What does gnuplot offer?

1.4 Is gnuplot suitable for scripting?

Yes. Gnuplot can read in files containing additional commands during an interactive session, or it can be run in batch mode by piping a pre-existing file or a stream of commands to stdin. Gnuplot is used as a back-end graphics driver by such higher-level mathematical packages as Octave, and can easily be wrapped in a cgi script for use as a web-driven plot generator.

1.5 Can I run gnuplot on my computer?

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

1.6 Legalities

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?

1.7 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.

1.8 Where do I get further information?

See the main gnuplot web page http://www.gnuplot.info and references therein, mainly gnuplot links http://gnuplot.sourceforge.net/links.html.

Some documentation and tutorials are available in other languages than English. See http://gnuplot.sourceforge.net/help.html, section "Localized learning pages about gnuplot", for the most up-to-date list.

2 Setting it up

2.1 What is the current version of gnuplot?

The current released version of gnuplot is 4.0.

2.2 Where can I get gnuplot?

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

The source distribution ("gnuplot-4.0.0.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

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

The following platform-specific sites below still exist, but may or may not still hold gnuplot executables.

2.3 Where can I get current development version of gnuplot?

The development version of gnuplot is availble as a cvs source tree online for direct browsing from http://www.sourceforge.net/projects/gnuplot/, section "CVS". You can download all current sources according to the documentation therein; for example by a sequence of commands like

  export CVSROOT=:pserver:anonymous@cvs.gnuplot.sourceforge.net:/cvsroot/gnuplot
  cvs login
  cvs -z3 checkout gnuplot

Further, before the ./configure command of gnuplot compilation phase, you have to execute ./prepare to create the up-to-date configure files.

There are no official preliminary binary releases of gnuplot: you have to compile it yourself. However, you may find unofficial binary releases for some platforms, like OS/2, Windows or Macintosh.

Important note: questions related to the development version should go to gnuplot-beta@lists.sourceforge.net.

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

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

2.5 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

The documentation is built during installation if you have LATEX installed on your system, look in the directories docs and tutorial. make pdf in the docs subdirectory will make a gnuplot.pdf hypertext file ready for browsing or printing.

Online gnuplot documentation is available at http://gnuplot.sourceforge.net/documentation.html.

(Obsolete?) PostScript copies of the documentation can be ftp'd from ftp.gnuplot.info in /pub/gnuplot, as manual.ps.Z and tutorial.ps.Z. Documentation about gnuplot is available at the gnuplot distribution sites in the files gpdoc.zip and gpdoc2.zip.

2.6 Worked examples

There is a directory of worked examples in the the source distribution. These examples, and the resulting plots, may also be found at http://gnuplot.sourceforge.net/demo/.

2.7 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 the patch utility, and possibly also automake and autoconf. On many UNIX systems these will already be installed; If they aren't, you can find them wherever GNU software is archived. Typical command for applying a patch is patch -p0 <newfunctionality.diff.

There is repository of contributed patches in the "Patches" section on gnuplot's sourceforge site http://www.sourceforge.net/projects/gnuplot/.

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 gnuplot-info@lists.sourceforge.net. 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@lists.sourceforge.net 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)

Using the platform-independent way of restoring terminal by set term push/pop commands, do it by

gnuplot> set terminal postscript eps color lw 15 "Helvetica" 20
gnuplot> set out 'a.eps'
gnuplot> replot
gnuplot> set term pop
The command set term pop without a previous corresponding set term push switches the terminal back to the startup terminal, e.g. x11, pm or win.

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 (PostScript, emf, svg, pdf, TEX, LATEX, etc) should be preferred, as you can scale your graph later to the right size.

Details depend on which 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 [color] command. Note that it is a good idea to check and correct the bounding box of the graphs in the eps files (manually or by the fixbb script from gnuplot webpage), as you have to correct this box for any eps figure produced by whichever program. Some (most?) word processors do not preview the actual image in the eps file, and you have to add the preview image yourself. You can use the GSView viewer for this (available for OS/2, Windows and X11), or some Unix ps tool. Note that the preview image increases size of the eps file; the smallest increase you may get by choosing Tiff 6 Packbits.

Into some office applications, like OpenOffice.org, or into applications in the Windows world, you can insert vectorial images produces by the emf terminal type.

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 OS/2 and MS-DOS), you can use emTeX, otherwise use the LATEX terminal type, which generates a picture environment. You can also use epslatex to separate the graphics and text parts. Other possibilities include pslatex or pstex terminals, and metafont or metapost terminals.

With TEX processed by pdftex or pdflatex, you can use png, jpeg and pdf terminal types. You can also use the postscript eps terminal and convert the eps file externally to pdf by epstopdf. Another choice is the epslatex terminal, after converting the eps part to pdf as above (the TEX part can remain unchanged).

Most word processors can import bitmap images (png, pbm, etc). The disadvantage of this approach is that the resolution of your plot is limited by the size of the plot at the time it is generated by gnuplot, which is generally a much lower resolution than the document will eventually be printed in.

Under IBM OS/2, MacOS and Micro$oft Windows you can use the clipboard to copy your graph and paste it into your favourite word processor.

The mif terminal type produces output for FrameMaker.

3.4 How do I edit or post-process a gnuplot graph?

This depends on the terminal type you use.

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

Gnuplot offers a variety of commands to set line and point properties, including color, thickness, point shape, etc. The command test will display a test page for the currently selected terminal type showing the available pre-defined combinations of color, size, shape, etc. The set style command can be used to define additional combinations.

3.6 How do I generate plots in GIF format?

GIF support was provided by an external library, libgd. Version 1.6 of the gd library dropped support for gif in favour of the superior png format. More recent versions of libgd also support jpeg output. If your installation of gnuplot is linked to the gd library, you will get support for whatever formats (gif, png, jpeg) are in that version of libgd.

Thus, nowadays, the usual way is to output the image as png and then use your favourite program to convert it into gif, either using command line (e.g. convert f.png f.gif or nconvert -out gif f.png) or by any GUI program. Another possibility is to output the image as (encapsulated) postscript and convert (export) it into gif or png by ghostscript, e.g. convert -density 150 f.eps f.gif or by any ghostscript-based GUI like gsview, gv or kghostview.

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://www.lcdf.org/ eddietwo/gifsicle or gifmerge http://the-labs.com/GIFMerge.

mpeg_encode will encode a sequence of images into an mpeg format movie.

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 pop
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.

3.9 How to fill an area between two curves

A plot with filled area between two given curves requires a parametric plot with filledcurves closed. The example below demonstrates this for two curves f(x) and g(x) with a tricky "folded" parameter t:

set parametric
set xrange [0:xmax]
set trange [0:2*xmax]
path(t) = ( t<= xmax ? f(t) : g(2*xmax-t) )
fold(t) = (t <=xmax ? t : 2*xmax - t)
plot fold(t),path(t) with filledcurves closed

Note that the above code fills area between the two curves, not area satisfying inequality g(x)<f(x). If you want the latter, you should use the ternary operator in path(t) to return an undefined value (0/0) if the inequality is not satisfied.

See the documentation for help parametric, help filledcurves, and help ternary.

3.10 Pm3d splot from a datafile does not draw anything

You do set pm3d; splot 'a.dat' and no plot but colorbox appears. Obviously, there is no blank line in between two subsequent scans (isolines) in the data file. Add blank lines! If you are curious what this means, then don't hesitate to look to files like demo/glass.dat or demo/triangle.dat in the gnuplot demo directory.

You can find useful the following awk script (call it e.g. addblanks.awk) which adds blank lines to a data file whenever number in the first column changes:

/[:blank:]*#/ {next} # ignore comments (lines starting with #)
NF < 3 {next} # ignore lines which don't have at least 3 columns
$1 != prev {printf "\n"; prev=$1} # print blank line
{print} # print the line
Then, either preprocess your data file by command awk -f addblanks.awk <a.dat or plot the datafile under a unixish platform by gnuplot> splot "<awk -f addblanks.awk a.dat".

3.11 Drawing a (color) map, i.e. 2D projection of 3D data

Use set view map; unset surface or set pm3d map rather than set view 180,0. The latter facilitates drawing matrices or data files as maps, even without the necessity for matrix-like data organization (gridding). It is possible to decrease the output postscript file size by postprocessing it by pm3dCompress.awk or pm3dConvertToImage.awk.

Note there is a new plotting style with image for plotting 2D color images with support for almost arbitrary text or binary files in "Patches" section on gnuplot's sourceforge site http://www.sourceforge.net/projects/gnuplot/.

3.12 How to overlay dots/points scatter plot onto a pm3d map/surface

Use the explicit (see also implicit) switch of the pm3d style:

gnuplot> set pm3d explicit
gnuplot> splot x with pm3d, x*y with points

3.13 How to draw black contour plot, and contours with labels

Drawing contour plot in one colour requires to write contours into a temporary file using the table terminal:

set contour base; set cntrparam levels 15; unset surface; set view map
splot x*x+y*y; pause -1
set term table; set out 'contour.dat'
replot; set out; set term pop
Now, for drawing it in 2D, do
plot 'contour.dat' with line -1
end for contours in 3D do
# Change single blank lines to double blank lines
!awk "NF<2{printf\"\n\"}{print}" <contour.dat >contour1.dat
plot 'contour1.dat' with line -1
See also the following question "How to overlay contour plot over pm3d map/surface".

Labelling contours by their z-value can be achieved by a suitable script generating automatically the appropriate set label commands; you can find one at gnuplot scripts page http://gnuplot.sourceforge.net/scripts/index.html#tricks-here.

3.14 How to overlay contour plot over pm3d map/surface

It is necessary to write contours into a temporary file using the table terminal, and then use this file in the final drawing without set contours. The following example demonstrates this for a map; for surface, remove set pm3d map and put set ticslevel 0.

# Write contours of function  x*x-y*y  to a (temporary) file
set term table
set out 'contour.dat'
set contour base; set cntrparam level 20
unset surface
splot x*x-y*y
set out; set term pop

# Change single blank lines to double blank lines
!awk "NF<2{printf\"\n\"}{print}" <contour.dat >contour1.dat

# Draw the plot
set palette gray
set palette gamma 2.5
set pm3d map
set pm3d explicit
splot x*x+y*y with pm3d, 'contour1.dat' with line -1
!rm contour.dat contour1.dat
The last command deletes the two temporary files.

3.15 Color facets with pm3d

It is possible to draw colors facets of a 3D objects, organized in such a file:

# triangle 1
x0 y0 z0 <c0>
x1 y1 z1 <c1>

x2 y2 z2 <c2>
x2 y2 z2 <c2>

# triangle 2
x y z

Notice the positioning single and double blank line. <c> is an optional color.

Then plot it by (either of splot's):

set pm3d
set style data pm3d
splot 'facets.dat'
splot 'facets_with_color.dat' using 1:2:3:4

Note that you avoid surface lines by set style data pm3d or splot ... with pm3d.

In the above example, pm3d displays triangles as independent surfaces. They are plotted one surface after another as found in the data file. Parts overlapping in 2D projection are overdrawn.

Gnuplot is not 3D modeling program. Its hidden routines apply for points and lines, but not for faces. Without handling the data as a collection of faces, there would be no surface anything could be hidden behind. The 'hidden3d' algorithm works by using the input data in two ways: first, to set up a collection of triangles (made from a mesh of quadrangles) that form the surface, second as a collection of edges. It then goes through all those edges, checking what parts of them are not hidden behind any faces, and draws those.

Consequently, gnuplot won't draw your surface or 3D object as a virtual reality. It works OK for set pm3d map but for true 3D you would be probably more happy writing a convertor of your facets into a VRML file.

3.16 Palette for printing my color map on color as well as blank&white printer?

I think it is this one, for example: set palette rgbformulae -25,-24,-32. Can somebody prove this?

4 Wanted features

4.1 What's new in gnuplot 3.7, 4.0 etc?

Too many things to be named here. Please refer to the NEWS file in the source distribution, or the News section in the gnuplot documentation.

4.2 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 file gnuplot/src/term.h, and recompile.

4.3 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.

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

Use the style with boxes for bar charts. To get filled boxes, use set style fill.

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

There is a large patch (#606169) against the development version on SourceForge awaiting inclusion in a future release of gnuplot. This adds a new plotting style with histograms, and supports both clustered histograms and stacked histograms.

4.5 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

4.6 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.

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

Yes. You can have 2 x- and 2 y-axes per plot. The additional axes are called x2 and y2. See help plot.

4.9 Can I put both commands and data 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

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

The enhanced option in some terminals (currently postscript, Presentation Manager, png, pdf, and x11) lets you use sub- and superscripts. It also allows to use Greek letters and symbols via symbol fonts, to the extent that these are supported by the underlying font libraries on your system. Versions through 2.0.15 of libgd (needed for png and jpeg) must be patched in order to handle symbol fonts.

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

4.11 How do I include accented characters

To obtain accented characters like ü or n in your labels you should use 8bit 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

Consequently, you can type labels in Czech, French, Hungarian, Russian... by means of an appropriate set encoding. However, you cannot mix two encodings in one file (e.g. accents for west and east latin encodings). That you can only do with a TEX output.

4.12 Can I do 1:1 scaling of axes?

Use set size square.

4.13 Can I put different text sizes into my plots?

Some terminals can, others can't. Some allow you to choose a font size for the entire plot. Terminals supporting the "enhanced text" mode (like postscript, pm, x11, png, pdf) allow you to change fonts and text sizes within a plot. Look at the help for these terminals.

4.14 How do I skip data points?

By specifying ? as a data value, as in

        1 2
        2 3
        3 ?
        4 5

See also set missing. See also set datafile commentschars for specifying comment characters in data files.

4.15 How do I plot every nth point?

This can be specified with various options for the command plot, for example plot 'a.dat' every 2.

4.16 How do I plot a vertical line?

Depending on context, the main methods are:

4.17 How do I plot data files

Easily: by a command plot 'a.dat'. In 3D, use splot 'a.dat' - but don't forget to put a blank line in between two subsequent scans (isolines), otherwise you will get an error that the data is not gridded; see also question 3.10. If your data are not gridded, then use set dgrid3d {many options}.

4.18 How do I replot multiplot drawing

You cannot directly: gnuplot supports replot command, not remultiplot. You have to write the complete sequence of commands since set multiplot till unset multiplot into a script file. Then you can load the script into gnuplot as many times as you need for replotting the drawing to different terminals or output files.

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 gnuplot-bug@lists.sourceforge.net.

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?

On systems supporting pipes, you can pipe commands to gnuplot from other programs. Many applications with gnuplot as the graphics engine, like Octave (http://www.octave.org), uses this method. This also works from a cgi script to drive gnuplot from a forms-based web page.

John Campbell jdc@nauvax.ucc.nau.edu modified a much earlier version of gnuplot (3.5) to be a library of C subroutines callable from a C program. Gnuplot itself has changed radically since then, and we are not aware of any plans to create a similar library based on the current version.

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

Many extensions or patches are available on the "Patches" page of the gnuplot development site http://sourceforge.net/tracker/?group_id=2055&atid=302055. The current development version will generally include some of these being debugged for inclusion in a later official release of gnuplot.

Older extensions, which may or may not work with the current version, are available from ftp.ucc.ie in /pub/gnuplot/contrib/.

Some extensions available:

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

Gnuplot has been and is a plotting program, not a data processing or mathematical program suite. Therefore gnuplot can't do that. Look into the demo file "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. Octave is licensed under GPL, and in principle, it is a free Matlab clone. 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.octave.org. 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 Mouse in my interactive terminal does not work

If your mouse is not working, try to hit 'm' in the interactive terminal to switch mousing on/off. See below for the list of supported interactive terminals.

If it still does not run, then either gnuplot has not been configured or compiled with mouse support, or you have not properly installed it, or running an older version of gnuplot (check your PATH).

If your gnuplot is running as the plotting engine of Octave under X11, then please put gset mouse into your $HOME/.octaverc. According to gnuplot's help x11, gnuplot under x11 running through a pipe needs set mouse to be executed before launching the x11 plot window.

5.7 How to use hotkeys in my interactive terminals

There are several hotkeys available in interactive terminals. Currently the following interactive terminals support hotkeys and mousing: OS/2 Presentation Manager, X11, Windows, and GGI. Hit 'h' in the terminal to get list of hotkeys. See help new or the What is New in 4.0 section in the docs for a brief guide over mousing and hotkeys. Further, you may read help mouse and help bind for more information.

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

If your patch is small, mail it to gnuplot-beta@lists.sourceforge.net, with a thorough description of what the patch is supposed to do, which version of gnuplot it is relative to, etc. Well, please do it always with respect to the current development version of gnuplot (see 'cvs' above).

Nowadays, the preferred way of submitting, commenting and upgrading patches are via 'Patches' section on http://www.sourceforge.net/projects/gnuplot/. You may want to send a note to gnuplot-beta@lists.sourceforge.net for more lively discussion.

5.9 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 gnuplot-beta in the body (not the subject) of the mail to Majordomo@lists.sourceforge.net.

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

5.10 Open questions for inclusion into the FAQ?


Please submit your questions (along with the answer) to gnuplot-beta@lists.sourceforge.net.

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.

The above filtering works seamlessly under Unixes and OS/2. It can work under MS Windows as well, but that is for experienced users: (A) When gnuplot has been compiled by cygwin with the unixish way of ./configure; make with X11 terminal instead of the 'windows' terminal. You have to run this under an X-server. This procedure is out of knowledge for usual users, but powerful for others. (B) Compile gnuplot yourself by makefile.mgw or makefile.cyg and set PIPES=1 therein. The drawback is that each wgnuplot.exe will be accompanied by a boring shell box.

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.

You can save the current terminal and restore it later without touching the filesystem by set term push and set term pop, respectively.

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) that is bounded by other functions in the x-y plane?

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 turn off <feature> in a plot?

Most gnuplot features are controlled by a corresponding set/unset command. If a feature is enabled by default, or by using set <feature>, then you should be able to turn it by using set no<feature>. However, the prefered syntax in version 4.0 is unset <feature>.

6.8 How do I call gnuplot from my own programs?

On unix-like systems, commands to gnuplot can be piped via stdin. Output from gnuplot's print command can be read via a named pipe. On M$ Windows platforms, due to the lacking standard input (stdin) in GUI programs, you need to use the helper program pgnuplot which should be included in your gnuplot for M$W distribution package. Reading gnuplot output may be impossible.

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 (character 264 in iso-latin-1 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).

6.10 How do a produce blank output page?

Well, you probably don't want a blank page, but page with a just a title (overprinting title in another graph in multiplot page):

reset; unset xtics; unset ytics
unset border; unset key
set title 'Title on an empty page'
plot [][0:1] 2

7 Common 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. Command which gnuplot_x11 will help you.

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, type help set zero.

7.4 Gnuplot is not plotting on the screen when run from command line via 'gnuplot filename.gp'

Obviously, it draws (unless there is an error in the script file), but the plot dissappears immediately when the script is completed.

Solution 1: Put a pause -1 after the plot command in the file, or at the file end.

Solution 2: Use command gnuplot filename.gp - (yes, dash is the last parameter) to stay in the interactive regime when the script completes.

Solution 3A: 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.

Solution 3B: On M$ Windows, you can also use either -persist or /noend.

Solution 4: For OS/2 PM terminal, use set term pm persist or set term pm server. For X11 terminal, use set term x11 persist.

7.5 My formulas (like 1/3) 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
gnuplot> print 1./3.

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 may 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 at least gnuplot 3.7. The LATEX2$\epsilon$-core no longer includes the commands "$\backslash$Diamond" and "$\backslash$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 an old bug and is fixed in newer releases.

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 mentioned in older documentation. You can currently find the version 3.7 examples at http://www.gnuplot.vt.edu/gnuplot/gpdocs. Version 4.0 examples are at http://gnuplot.sourceforge.net/demo.

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;
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. Additional substantial contributors to version 4.0 include Ethan Merritt, Petr Mikulík and Johannes Zellner.

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. Revised for gnuplot 4.0 release by Petr Mikulík and Ethan Merritt.


Gnuplot FAQ

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Shigeharu TAKENO 2005年 3月 18日