Maemo "optification" was added

[gnuplot] / FAQ

                                  Gnuplot FAQ

   This document deals with gnuplot version 4.2 which is the latest official
   release as of February 2007.
   Its version is $Revision: 1.16.2.2 $, dated $Date: 2007/02/25 13:18:34 $.

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 What does gnuplot offer?
          * 1.4 Is gnuplot suitable for scripting?
          * 1.5 Can I run gnuplot on my computer?
          * 1.6 Legalities
          * 1.7 Does gnuplot have anything to do with the FSF and the GNU
            project?
          * 1.8 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 Where can I get current development version of gnuplot?
          * 2.4 How do I get gnuplot to compile on my system?
          * 2.5 What documentation is there, and how do I get it?
          * 2.6 Worked examples
          * 2.7 How do I modify gnuplot, and apply 'patches'?
     * 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 edit or 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 GIF format?
          * 3.7 Can I animate my graphs?
          * 3.8 How do I plot implicit defined graphs?
          * 3.9 How to fill an area between two curves
          * 3.10 Pm3d splot from a datafile does not draw anything
          * 3.11 Drawing a (color) map, i.e. 2D projection of 3D data
          * 3.12 How to overlay dots/points scatter plot onto a pm3d
            map/surface
          * 3.13 How to draw black contour plot, and contours with labels
          * 3.14 How to overlay contour plot over pm3d map/surface
          * 3.15 Color facets with pm3d
          * 3.16 Palette for printing my color map on color as well as
            black&white printer?
     * 4 Wanted features
          * 4.1 What's new in gnuplot 3.7, 4.0, 4.2 etc?
          * 4.2 Does gnuplot support a driver for <graphics format>?
          * 4.3 Does gnuplot have hidden line removal?
          * 4.4 Does gnuplot support bar-charts/histograms/boxes?
          * 4.5 Does gnuplot support pie charts?
          * 4.6 Does gnuplot quarterly time charts?
          * 4.7 Can I put multiple pages on one page?
          * 4.8 Does gnuplot support multiple y-axes on a single plot?
          * 4.9 Can I put both commands and data into a single file?
          * 4.10 Can I put Greek letters and super/subscripts into my labels?
          * 4.11 How do I include accented characters
          * 4.12 Can I do 1:1 scaling of axes?
          * 4.13 Can I put different text sizes into my plots?
          * 4.14 How do I skip data points?
          * 4.15 How do I plot every nth point?
          * 4.16 How do I plot a vertical line?
          * 4.17 How do I plot data files
          * 4.18 How do I replot multiplot drawing
     * 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 Mouse in my interactive terminal does not work
          * 5.7 How to use hotkeys in my interactive terminals
          * 5.8 I have ported gnuplot to another system, or patched it. What
            do I do?
          * 5.9 I want to help in developing the next version of gnuplot.
            What can I do?
          * 5.10 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) that is bounded by other
            functions in the x-y plane?
          * 6.7 How do I turn off <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)?
          * 6.10 What if I need the Solar mass symbol?
          * 6.11 How do I produce blank output page?
     * 7 Common problems
          * 7.1 Help! None of my fonts work.
          * 7.2 Gnuplot is not plotting any points under X11! How come?
          * 7.3 Why does gnuplot ignore my very small numbers?
          * 7.4 Gnuplot is not plotting on the screen when run from command
            line via 'gnuplot filename.gp'
          * 7.5 My formulas (like 1/3) 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 I can't find the demos and example files at the URLs in the
            documentation!
          * 7.9 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?

   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?

     * Plotting two-dimensional functions and data points in many different
       styles (points, lines, error bars)
     * Plotting three-dimensional data points and surfaces in many different
       styles (contour plot, mesh)
     * Algebraic computation in integer, float and complex arithmetic
     * User-defined functions and hot-keys
     * Support for a large number of operating systems, graphics file formats
       and output devices
     * Extensive on-line help
     * TEX-like text formatting for labels, titles, axes, data points
     * Interactive command line editing and history (most platforms)

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 4.2.

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-4.2.0.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
     * 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/

   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/.

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

     * 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 for example gp37dos.zip, gp37dj.zip, gp37w16.zip,
       gp37mgw.zip, gnuplot3.7cyg.zip. OS/2 binaries are called gp37os2.zip.

     * 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.

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

   cvs -d:pserver:anonymous@cvs.sourceforge.net:/cvsroot/gnuplot login
   cvs -z3 -d:pserver:anonymous@cvs.sourceforge.net:/cvsroot/gnuplot co -P gnuplot

   or (in bash)

   export CVSROOT=:pserver:anonymous@cvs.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.

     * For Unix, use ./configure (or ./configure -prefix=$HOME/usr for an
       installation for a single user), make and finally make install or make
       install-strip, the latter for smaller executables without debugging
       information. If you want to make a RPM package, then replace the
       latest step by checkinstall or checkinstall make install-strip,
       supposing the package checkinstall on your machine.
     * For DOS, if you are using bash and DJGPP, you can just run
       djconfig.sh.
     * For other platforms, copy the relevant makefile (e.g. makefile.os2 for
       OS/2, or makefile.mgw or makefile.cyg for Windows) from config/ to
       src/, optionally update options in the makefile's header, then change
       directory to src and run make.

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

     * 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 TEX only

   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)
 !
 gnuplot>

   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.

   Some office Windows applications, also OpenOffice.org, can handle vector
   images produces by the emf terminal. OpenOffice.org can also read
   AutoCAD's dxf format, as well as SVG thanks to SVG Import Filter
   http://www.ipd.uni-karlsruhe.de/ hauma/svg-import/.

   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.

     * X11 toolkits: You can use the terminal type fig 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.

     * You may use the svg terminal (scalable vector graphics), which can be
       further edited by a svg editor, e.g. Inkscape
       (http://www.inkscape.org), Sodipodi (http://sodipodi.sourceforge.net),
       Sketch (http://sketch.sourceforge.net) or Dia
       (http://www.lysator.liu.se/ alla/dia), or loaded into OpenOffice.org
       with an on-fly conversion into OO.o Draw primitives.

     * PostScript or PDF output can be edited directly by tools such as Adobe
       Illustrator or Acrobat, or can be converted to a variety of other
       editable vector formats by the pstoedit package. Pstoedit is available
       at http://www.pstoedit.net.

     * The mif terminal type produces an editable FrameMaker document.

     * The DXF format is the AutoCAD's format, editable by several other
       applications.

     * Bitmapped graphics (e.g. png, jpeg, pbm) can be edited using tools
       such as ImageMagick or Gimp. In general, you should use a vector
       graphics program to post-process vector graphic formats, and a
       pixel-based editing program to post-process pixel graphics.

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 is provided by an external library, libgd
   (http://www.libgd.org). Old versions of gd (versions 1.2 to 1.4) produce
   only GIF output. Versions 1.6 to 2.0.27 did not support GIF output because
   of patent concerns. However versions 1.6 and newer support PNG outputs,
   and 1.7 and newer support JPEG outputs. Version 2.0.28 of the Boutell gd
   library restored GIF functionality, and 2.0.29 added support for GIF
   animation. 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 gd.

   In any case, it is easy to convert from one format to another. To convert
   a PNG output into GIF, you can either use the command line (e.g. convert
   f.png f.gif or nconvert -out gif f.png) or 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.

   If your installation of gnuplot is linked with gd 2.0.29 or newer (see
   previous entry), the gif terminal can generate directly an animated GIF.

   Otherwise, have a look at the tool whirlgif 3.04, available at
   http://www.danbbs.dk/ dino/whirlgif. It reads run-length encoded GIF files
   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> # An 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> unset surface
 gnuplot> set table 'curve.dat'
 gnuplot> splot f(x,y)
 gnuplot> unset table
 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
 f(x)=cos(x)
 g(x)=sin(x)
 xmax=pi/4
 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

   Well, it is very simple even though it is hard to discover: unset clabel.

 set contour both; set cntr levels 100
 unset clabel
 unset surface
 splot x*y with line lt -1
 pause -1
 splot x*y with line palette

   Another solution 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 table 'contour.dat'
 replot
 unset table

   Now, for drawing it in 2D, do

 reset
 plot 'contour.dat' with line -1

   and for contours in 3D do

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

   This requires you 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 contour base; set cntrparam level 20
 unset surface
 set table 'contour.dat'
 splot x*x-y*y
 unset table

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

 # Draw the plot
 reset
 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 lt -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 black&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, 4.2 etc?

   Too many things to be named here. Please refer to the NEWS file in the
   source distribution, or the "New features" 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?

   Yes.

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

   Various clustered and stacked histogram styles are supported in gnuplot
   version 4.2 as separate style types.

   In older gnuplot versions you can 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. This may be useful with older
   versions of gnuplot. Please have a look at
   http://www.usf.uni-osnabrueck.de/ breiter/tools/gnuplot/barchart.en.html.

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
 e

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 u: 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).

   A more general solution is to use UTF-8 encoded fonts, and type the UTF-8
   characters directly into gnuplot. This works for many terminal types but
   not, unfortunately, PostScript.

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:
     * 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

4.17 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:
     * date-errorbar: allows dates in the hi/lo fields for errorbars.
     * perltk: A perl/tk canvas widget.
     * polyg.patch: Implements a polygon plotting style.
     * xgfe: graphical front end using the Qt widgets available at
       http://www.tug.org/tex-archive/graphics/gnuplot/contrib/.
     * Gnuplot.py: A python package to create graphs from within python. More
       information at http://gnuplot-py.sourceforge.net.

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 set mouse into your $HOME/.gnuplot (preferred than putting
   gset mouse into $HOME/.octaverc). This is needed only for gnuplot 4.0:
   according to its help x11_mouse, gnuplot 4.0 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, WX, and GGI. Hit 'h' in the terminal
   to get list of hotkeys. See help new-features or the Features introduced
   in version 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 since 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)?

   The most straightforward way is to use a UTF-8 font, and type in the
   $\hbar$ character (Unicode code point #x210F) directly.

   This does not work in PostScript, however, so you must use approximations
   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}}.

   The reduced Planck's constant can be set very easily by using the
   AMS-LaTeX PostScript fonts which are available from
   http://www.ams.org/tex/amsfonts.html (also included in many LaTeX
   distributions). Gnuplot (confer the help about fontpath) and the
   PostScript interpreter (usually Ghostscript) have to know where the file
   msbm10.pfb (or msbm10.pfa) resides. Use {/MSBM10 \175} to produce \hslash
   which is a "h" superimposed by a sloped bar. The standard \hbar
   (horizontal bar) has the octal code 176. Please note that h-bar exists
   only as an italic type.

6.10 What if I need the Solar mass symbol?

   As with Planck's constant, the most straightforward way is to use a UTF-8
   font, and type in the $\odot$ character (Unicode code point #x2299)
   directly.

6.11 How do I 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 Help! None of my fonts work.

   Gnuplot does not do font handling by itself; it must necessarily leave
   that to the individual device support libraries. Unfortunately, this means
   that different terminal types need different help in finding fonts. Here
   are some quick hints. For more detailed information please see the gnuplot
   documentation for the specific terminal type you are having problems with.

   png/jpeg/gif
           These terminal types use the libgd support library, which searches
           for fonts in the directories given in the environmental variable
           GDFONTPATH. Once you get libgd fontpaths sorted out, you will
           probably want to set a default font for gnuplot. For example:
           setenv GNUPLOT_DEFAULT_GDFONT verdana

   pdf
           The libpdf support library should have come with an associated
           font configuration file, usually installed as
           /usr/local/share/pdflib.upr. The environmental variable
           PDFLIBRESOURCE should point to this file.

   post
           PostScript font names are not resolved until the document is
           printed. Gnuplot does not know what fonts are available to your
           printer, so it will accept any font name you give it. However, it
           is possible to bundle a font with the gnuplot output; please see
           the instructions given by gnuplot's internal command ``help set
           term post fontfile''.

   svg
           Font handling is viewer-dependent.

   x11
           The x11 terminal uses the normal x11 font server mechanism. The
           only tricky bit is that in order to use multi-byte fonts you must
           explicitly say so:

 set term x11 font "mbfont:sazanami mincho,vera,20"

   win
           Right-click in the control window, then select "Choose font" from
           the pull-down menu.

   wxt
           On linux systems, the wxt terminal can find fonts indexed by the
           fontconfig utility.

7.2 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.

7.3 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
                 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 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!

   The LATEX2$\epsilon$-core no longer includes the commands
   "$\backslash$Diamond" and "$\backslash$Box"; they are included in the
   latexsym package. Other symbols are taken from the asmsymb package. Both
   of these are part of the base distribution and thus part of any LaTeX
   implementation. Please remember to include these packages in your LaTeX
   document.

7.8 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 find the version 4.0 examples at
   http://gnuplot.sourceforge.net/demo. Version 4.2 examples are at
   http://gnuplot.sourceforge.net/demo_4.2.

7.9 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. Additional substantial contributors to version 4.0 include Ethan
   Merritt, Petr Mikulik 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 Mikulik and Ethan Merritt. Revised for gnuplot 4.2 release
   by Petr Mikulik and Ethan Merritt.