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* Please note that this is not the current official FAQ since
* I have upgraded the info in answer 4.0 - dd

Archive-name: graphics/gnuplot-faq
Version: Mon Sep 23 04:23:01 CES 1996
Posting-frequency: every 14 days
URL: http://www.uni-karlsruhe.de/~ig25/gnuplot-faq/

   comp.graphics.apps.gnuplot

        comp.graphics.apps.gnuplot FAQ (Frequent Answered Questions)

   This is the FAQ (Frequently Answered Questions) list of the
   comp.graphics.apps.gnuplot newsgroup, which discusses the gnuplot
   program for plotting 2D - and 3D - graphs.

   Most of the information in this document came from public discussion
   on comp.graphics.apps.gnuplot; quotations are believed to be in the
   public domain.

   If you are reading this via WWW, and you can't access the individual
   pages, please select here, then try again.

   Here's a list of the questions. If you are looking for the answer for
   a specific question, look for the string Qx.x: at the beginning of a
   line, with x.x being the question number. Sections in this FAQ are
     * 0. Meta-Questions
     * 1. General Information
     * 2. Setting it up
     * 3. Working with it
     * 4. Wanted features
     * 5. Miscellaneous
     * 6. Making life easier
     * 7. Known problems
     * 8. Credits


Questions:

  Section 0: Meta - Questions

     * Q0.1: Where do I get this document?
     * Q0.2: Where do I send comments about this document?

  Section 1: General Information

     * Q1.1: What is gnuplot?
     * Q1.2: How did it come about and why is it called gnuplot?
     * Q1.3: Does gnuplot have anything to do with the FSF and the
       GNU project?
     * Q1.4: What does gnuplot offer?
     * Q1.5: Is gnuplot suitable for batch processing?
     * Q1.6: Can I run gnuplot on my computer?

  Section 2: Setting it up

     * Q2.1: What is the current version of gnuplot?
     * Q2.2: Where can I get gnuplot?
     * Q2.3: How do I get gnuplot to compile on my system?
     * Q2.4: What documentation is there, and how do I get it?

  Section 3: Working with it

     * Q3.1: How do I get help?
     * Q3.2: How do I print out my graphs?
     * Q3.3: How do I include my graphs in <word processor>?
     * Q3.4: How do I post-process a gnuplot graph?
     * Q3.5: How do I change symbol size, line thickness and the
       like?
     * Q3.6: How do I generate plots in GIF format?

  Section 4: Wanted features

     * Q4.0: What's new in gnuplot 3.6?
     * Q4.1: Does gnuplot have hidden line removal?
     * Q4.2: Does gnuplot support bar-charts/histograms/boxes?
     * Q4.3: Does gnuplot support multiple y-axes on a single plot?
     * Q4.4: Can I put multiple plots on a single page?
     * Q4.5: Can I put both data files and commands into a single
       file?
     * Q4.6: Can I put Greek letters and super/subscripts into my
       labels?
     * Q4.7 Can I do 1:1 scaling of axes?
     * Q4.8: Can I put tic marks for x and y axes into 3d plots?
     * Q4.9: Does gnuplot support a driver for <graphics format>?
     * Q4.10: Can I put different text sizes into my plots?
     * Q4.11: How do I modify gnuplot?
     * Q4.12: How do I skip data points?

  Section 5: Miscellaneous

     * Q5.1: I've found a bug, what do I do?
     * Q5.2: Can I use gnuplot routines for my own programs?
     * Q5.3: What extensions have people made to gnuplot? Where can I
       get them?
     * Q5.4: Can I do heavy-duty data processing with gnuplot?
     * Q5.5: I have ported gnuplot to another system, or patched it.
       What do I do?
     * Q5.6: I want to help in developing gnuplot 3.6. What can I do?

  Section 6: Making life easier

     * Q6.1: How do I plot two functions in non-overlapping regions?
     * Q6.2: How do I run my data through a filter before plotting?
     * Q6.3: How do I make it easier to use gnuplot with LaTeX?
     * Q6.4: How do I save and restore my settings?
     * Q6.5: How do I plot lines (not grids) using splot?
     * Q6.6: How do I plot a function f(x,y) which is bounded by
       other functions in the x-y plain?
     * Q6.7: How do I get rid of <feature in a plot>?
     * Q6.8: How do I call gnuplot from my own programs ?

  Section 7: Known Problems

     * Q7.1: Gnuplot is not plotting any points under X11! How come?
     * Q7.2: My isoline data generated by a Fortran program is not
       handled correctly. What can I do?
     * Q7.3: Why does gnuplot ignore my very small numbers?
     * Q7.4: Gnuplot is plotting nothing when run via gnuplot
       <filename>! What can I do?
     * Q7.5: My formulas are giving me nonsense results! What's going
       on?
     * Q7.6: My Linux gnuplot complains about a missing gnuplot_x11.
       What is wrong?
     * Q7.7: set output 'filename' isn't outputting everything it
       should!

  Section 8: Credits

  Section 0: Meta-Questions.

   Q0.1: Where do I get this document?
          This document is posted about once every two weeks to the
          newsgroups comp.graphics.apps.gnuplot, comp.answers and
          news.answers. Like many other FAQ's, its newest (plaintext)
          version is available via anonymous ftp from
          ftp://rtfm.mit.edu/pub/usenet/news.answers/graphics/gnuplot
          -faq.

          If you have access to the WWW, you can get the newest version
          of this document from
          http://www.uni-karlsruhe.de/~ig25/gnuplot-faq/

   Q0.2: Where do I send comments about this document?
          Send comments, suggestions etc. via e-mail to Thomas
          Koenig, Thomas.Koenig@ciw.uni-karlsruhe.de or
          ig25@dkauni2.bitnet.


  Section 1: General Information

   Q1.1: What is gnuplot?
          Gnuplot is a command-driven interactive function plotting
          program. It can be used to plot functions and data points in
          both two- and three- dimensional plots in many different
          formats, and will accommodate many of the needs of today's
          scientists for graphic data representation. Gnuplot is
          copyrighted, but freely distributable; you don't have to pay
          for it.

   Q1.2: 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.

   Q1.3: Does gnuplot have anything to do with the FSF and the GNU
          project?
          Gnuplot is neither written nor maintained by the FSF. It is not
          covered by the General Public License, either.

          However, the FSF has decided to distribute gnuplot as part of
          the GNU system, because it is useful, redistributable software.

   Q1.4: What does gnuplot offer?

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

   Q1.5: Is gnuplot suitable for batch processing?
          Yes. You can read in files from the command line, or you can
          redirect your standard input to read from a file. Both data and
          command files can be generated automatically, from data
          acquisition programs or whatever else you use.

   Q1.6: Can I run gnuplot on my computer?
          Gnuplot is available for a number of platforms. These are: Unix
          (X11 and NeXTSTEP), VAX/VMS, OS/2, MS-DOS, Amiga, MS-Windows,
          OS-9/68k, Atari ST and the Macintosh. Modifications for NEC
          PC-9801 are said to exist (where?).


  Section 2: Setting it up

   Q2.1: What is the current version of gnuplot?
          The current version of gnuplot is 3.5, which is a bugfix
          release over 3.4.

          Version 3.6 is in beta status. Please note that this is still
          unstable, and may not compile correctly on your system.

   Q2.2: Where can I get gnuplot?
          All of the later addresses refer to ftp sites. Please note that
          it is preferable for you to use the symbolic name, rather than
          the IP address given in brackets, because that address is much
          more subject to change.

          The official distribution site for the gnuplot source is
          ftp.dartmouth.edu [129.170.16.4, soon to be 129.170.8.11],
          the file is called /pub/gnuplot/gnuplot3.5.tar.Z. Official
          mirrors of that distribution are (for Australia)
          ftp.monash.edu.au [130.194.11.18] and (for Europe)
          irisa.irisa.fr [131.254.254.2]. You can also get it from your
          friendly neighbourhood comp.sources.misc archive.

          MS-DOS and MS-Windows binaries are available from

          + oak.oakland.edu (North America) [141.210.10.117] as
            /Simtel/msdos/plot/gpt35*.zip,
          + garbo.uwasa.fi (Europe) [193.166.120.5] as
            /pc/plot/gpt35*.zip and
          + archie.au (Australia) [139.130.4.6] as
            micros/pc/oak/plot/gpt35*.zip.

          The files are: gpt35doc.zip, gpt35exe.zip, gpt35src.zip and
          gpt35win.zip.

          There is a special MS-DOS version for 386 or better processors;
          it is available from the official gnuplot sites as DOS34.zip.

          OS/2 2.x binaries are at ftp-os2.nmsu.edu [128.123.35.151],
          in /os2/2.x/unix/gnuplt35.zip.

          Amiga sources and binaries are available from ftp.wustl.edu
          [128.252.135.4] as /pub/aminet/util/gnu/gnuplot-3.5.lha; there
          are numerous mirrors of this distribution, for example
          ftp.uni-kl.de, oes.orst.edu or ftp.luth.se.

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

          A version for OS-9/68K can be found at cabrales.cs.wisc.edu
          [128.105.36.20] as /pub/OSK/GRAPHICS/gnuplot32x.tar.Z; it
          includes both X-Windows and non - X-windows versions.

          There is a version for the Macintosh at
          ftp://ftp.ee.gatech.edu/pub/mac/gnuplot/ which includes
          binaries for 68000-based Macs with and without FPU and native
          support for PowerMacs.

          Versions for the Atari ST and TT, which include some GEM
          windowing support, are available from
          ftp://ftp.uni-kl.de/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://ftp.csis.oita-u.ac.jp/pub/x68k/fj.binaries.x68000/vol
          2.

          People without ftp access can use an ftp-mail server; send a
          message saying 'help' to bitftp@pucc.bitnet (for BITNET only)
          or to ftpmail@ftp.dartmouth.edu.

          For a uuencoded copy of the the gnuplot sources (compressed tar
          file), send this as the body of a message to
          ftpmail@ftp.dartmouth.edu:


        open
        cd pub/gnuplot
        mode binary
        get gnuplot3.5.tar.Z
        quit

   If you have some problem, you might need to stick

        reply-to  <your-email-address-here>

   before all the above.

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

          You can obtain a beta release of gnuplot 3.6 from
          ftp://cmpc1.phys.soton.ac.uk/pub/.

   Q2.3: How do I get gnuplot to compile on my system?
          As you would any other installation. Read the files README and
          README.Install, edit the Makefile according to taste, and run
          make or whatever is suitable for your operating system.

          If you get a complaint about a missing file libplot.a or
          something similar when building gnuplot for X11, remove
          -DUNIXPLOT from the TERMFLAGS= line, remove -lplot from the
          DTBS= line and run again. If you are making X11 on a sun, type
          'make x11_sun'.

          For compiling gnuplot under Irix 5.2 and Irix 5.3, there is a
          patch in the file lvs.zip in the contrib directory at
          ftp.dartmouth.edu.

   Q2.4: What documentation is there, and how do I get it?
          The documentation is included in the source distribution. Look
          at the docs subdirectory, where you'll find

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

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

          Andy Liaw and Dick Crawford have written a 16-page user's
          guide. It is available from
          ftp://picard.tamu.edu/pub/gnuplot/ as gptug.tex (also get
          example.tex from the same directory), gptug.dvi or gptug.ps.

          At the same site, there's a two- page instruction sheet for the
          enhpost PostScript driver (see Q4.6 ) as enhpost.guide.ps
          and a short guide to gnuplot PostScript files, as gp-ps.doc.

          A Chinese translation of the gnuplot manual can be found on
          ftp://servers.nctu.edu.tw/misc/environment/NCTU_EV/classnot
          e/gnuplot.ps.gz .

          There is a WWW hompepage for gnuplot at
          http://www.cs.dartmouth.edu/gnuplot_info.html, which
          includes the reference manual and a demo.

          There are two more Chinese documents about gnuplot: a 72 - page
          User's guide
          ftp://phi.sinica.edu.tw/pub/aspac/doc/94/94002.ps.gz and a
          28 - page Touring Guide
          ftp://phi.sinica.edu.tw/pub/aspac/doc/95/95006.ps.gz. Both
          documents are in PostScript format and gzipped.


  Section 3: Working with it

   Q3.1: How do I get help?
          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.

          Post a question to comp.graphics.apps.gnuplot or send mail
          to the gatewayed mailing list info-gnuplot@dartmouth.edu. If
          you want to subscribe to the mailing list, send a mail to
          majordomo@dartmouth.edu with the body of the message being
          'subscribe info-gnuplot'. Please don't do this if you can get
          comp.graphics.apps.gnuplot directly. If you pose a
          question there, it is considered good form to solicit e-mail
          replies and post a summary.

   Q3.2: 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>

   Q3.3: 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.

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

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

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

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

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

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

          There is new version including lots of patches from the net
          that is not maintained by the author called netpbm, with the
          newest version called netpbm-7dec1993.tar.gz.

          Check archie (see Q2.2 ) for an archive site near you.

   Q3.4: How do I post-process a gnuplot graph?
          This depends on the terminal type you use.

          You can use the terminal type fig (you may need to recompile
          gnuplot to enable this terminal type, by putting #define FIG
          into <term.h>), and use the xfig drawing program to edit the
          plot afterwards.

          For PostScript output, you may be able to use the pstotgif
          script (which calls GhostScript) to convert PostScript into the
          format of the tgif drawing program. Tgif is also able to save
          in PostScript format.

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

          Another possibility for modifying PostScript output appears to
          be IslandDraw, a commercial drawing program for UNIX
          workstations.

          For Windows, there is another alternative, PageDraw. It can
          post-process AI (Adobe Illustrator) files, and has a converter
          from PostScript to AI. It can be downloaded from
          http://www.wix.com/PageDraw/.

   Q3.5: How do I change symbol size, line thickness and the like?
          Again, this depends on the terminal type. For PostScript, you
          can edit the generated PostScript file. An overview of what
          means what in the PostScript files gnuplot generates can be
          found at ftp://picard.tamu.edu/pub/gnuplot/ as gs-ps.doc.
          A general introduction to PostScript can be found at
          ftp://unix.hensa.ac.uk/pub/misc/ukc.reports/comp.sci/repor
          ts/ as 11-92.ps.Z.

   Q3.6: How do I generate plots in GIF format?
          In gnuplot version 3.5, use the pbm terminal and use the
          PBMPLUS package or other utilities to convert the resulting
          bitmap (see Q 3.3 for how to get the PBMPLUS package).

          In 3.6, there will be a gif terminal.


  Section 4: Wanted features

   Q4.0: What's new in gnuplot 3.6?
          Here's the WhatsNew file of the current beta release,
          patchlevel 319.


What's new in 3.6 ?

see version.c for a detailed list of recent changes

BUGS outstanding
  minor tics missing on HPUX ?
  problem with time on os/2 - optimiser bug ?
  sometimes hidden-line-removal throws up a logic error (now fixed ?)
  bounding box in pslatex (now fixed ? - please check)
  terminal settings get propagated when terminal is changed (now fixed ?)
  set ?range [] writeback is broken ? certainly for logscales.
  source file copyrights are out of date - what should go on new files ?
  to be documented - ms-windows cannot do wide, dashed lines (well, win32 can, but...)
  does not build on win16 or sun/cc (getting closer)

OTHER ISSUES
  set mapping spherical is not 'real' spherical polars
  terminals are no longer allowed to do their own scaling
  break up some of the drivers (eg epson and family) into their
    own files. *maybe* we can provide libraries of generic routines
    (particularly tex) which can be used by all interested drivers,
    and because they are a library, they are linked only if
    any relevant drivers are installed. bitmap.c could also be
    linked in this way.
  Now that all drivers are new format, do we need to explore separate
    compilation of the drivers into their own .obj files for DOS ?
  hidden line is SLOW, and throws up some logic errors
  have I got all os/2 and (in particular) mac changes ?
  filled boxes ?
  substution using backquotes should not have a length limit
  the source indentation stinks - may I pass it through gnu indent,
     or will that mess up use of patches which did not make it into
     the release.
     


  As always, there are outstanding contributed patches
 that I haven't yet installed (sorry), and half-promises for features
 that I've not had a chance to fulfill.


in this release
  suppress ! after a ! command in interactive mode
  address polar mode, but polar grid looks wrong..?

314
  misc bug fixes

310
  HBB's hidden3d fix
  latest gnuplot.doc and term/*.trm help sections
  configure --with-gnu-readline[=path]

in 309
  sorry Roger ; os2 keeps on improving, but I forget to announce it
   {and often incorporate it !}
  relative errors displayed in fit

in 306
  histeps style
  LINE WIDTH PATCH !  {but many structures passed by value ?}
  tolerate missing closing backquote at end of line
  no limit on output filename
  set key samplelen / spacing
  plot ... axis   alias for  plot ... axes
  Thomas Koenig's postscript test for reencoding on the fly [at last]
  multiplot clear for djsvga
  size option on gif driver
  
in 300
  FINALLY moved the axes syntax over to plot ... axes x1y1 ...
  3d fitting ; FIT_INDEX no longer supported/needed (see fit.dem)
  added data columns -1 for line and -2 for index, for 3d fit
  had another go at the VPATH stuff for configure / make  

in 297
  back out unwanted feature of basing tics on relative size/font
  add financebars / candlesticks - size controlled by set bar
  plot 'file' using 0:1 gives x=0,1,... as gnuplot 3.5
  optional keyword 'font' in set xlabel 'text' dx,dy [font] "font,size"
  fix undefined points in splines

in 293/294
  ICCCM export of the x-window (allow paste into compliant apps ie NTRIGUE)
  print "string", expression, "string", ...
  set size square has been generalised to
    set size { square | ratio <r> | noratio }
    where <r> is an aspect ratio of height / width
  (at last) Hans-Bernhard Br"oker's changes, including fit fix and
    new hidden line removal routine
  plot line is commited to replot line at last possible moment, so
    that typos in complex plot do not ruin everything
  time routines separated into time.c - option to use system time
   routines instead of the gnuplot ones. Undocumented command
   testtime 'format' 'string'  to assist testing of time routines
  small changes to the terminal handling : hide details in term.c
  new shared makefile strategy : makefile.all


in 273
  pslatex driver takes solid/dashed
  cgm driver (ms-office applications ?)
  accept  using ::4  as shorthand for  using 1:2:4
  accept lp as abbreviation of linesp

in 268
  asinh() etc
  gnuplot -persist  and  set term x11 [reset] <n>
  gif terminal driver [not new in this release, but not mentioned before]

in 261
  compile on windows NT
  /end and /noend options in windows gnuplot
  first attempt at  timecolumn() and tm_sec() family of functions
  splot 'file' matrix

in 248 (?)
  try *again* to fix the postscript bounding box
  ALL TERMINALS UPDATED (thanks Stefan !)
  Continue to move help out of gnuplot.doc into terminal driver files (thanks Joerg)
  address problems with splines in log scales - NOTE that we take logs
   and then fit splines
  %T in gprintf prints as %d not %f hence no trailing .0000
  set locale  only affects LC_TIME (for the moment ?)
  make start optional in series tics, ie accept
    set [xyz]tics {start,}step{,end}
  also, if start or end not specified, treat as computed, and autoextend
    plot to a multiple of tics

in 242
  allow negative ticslevel
  geometric series tics for logscale
  enhanced sprintf format for tics - extra format characters available
    %x %o %e %f %g  %t %T %l %L %s %S %c
  take plot size and driver into account when choosing tics
  accept x1y2 etc in place of first/second
  extra line in boxed key
  x2 label
  fonts for label
  strftime format for 'set time'
  more timeseries patches
  set locale
  try to fix postscript bounding box

in 224
  set clabel ['format']
  pstexdriver
  set encoding
  enhpost moved into post.trm
  index a:b:c for splot

in 194
  multiplot for splot

in 188
  os9 port
  set xrange [] reverse writeback
  allow mix of co-ordinate systems within an arrow/label posn
  initial multiplot support
  - doesn't yet check that terminal is capable, but there is a
    flags field added to the terminal entry to tell gnuplot about this.
    also, suspend() / resume() entry points which are to be called
    between plots of a multiplot.

in 178
   arbitrary length/number of columns in datafile
   accept double/quad-precision fortran numbers (1.23{dDqQ}4)
   - but not in scanf format string
   undefined fit parameters start at 1 rather than 1e-30
   - more chance of convergence / less change of unitary matrix
   WIN32 / Win-NT support
   table output can be read back in for data splot
   - hence gnuplot can be used to dgrid a datafile and write it out
   set missing 'string'
   - nominate a token as standing for missing values in datafile
   - not yet added to documentation
   updates to time-series stuff (so it doesn't break at 2000)
   - except it has become horribly non-portable :-(
   split graph3d.c into util3d.c and hidden3d.c

in 166
   set bar <size>
   - a number rather than just small or large
   allow different linetypes for grid at major and minor tics
   a few more set no* commands for consistency.
   initial go at implementing tic mirrors and axes for splot
   - no ztic axis yet (or no zzeroaxis)
   - tics on axes are not hidden by surface
   attempt to make sin(x) behave as expected when set angle degrees
   - gives answers if x is complex, but I dont know if they are correct
     - acos(cos(x)) seems to give x, so at least its consistent
   - fix a bug which made acos(cos({0,1})) undefined
   new grass.trm

in release 162/164
   set size [{no}square] x,y  - tries to plot with aspect ratio 1
   - seems to work great for postscript
   - please check with your favourite driver
   - uses relative sizes of tics to determine required size.
   posn for key, labels and arrows can be in one of 4 co-ordinate systems
   - first_axes (default)
   - second_axes (for plot..second)
   - graph  (0,0 -> 1,1 = plotting area)
   - screen (0,0 -> 1,1 = whole screen)
   - arrows needn't have endpoints in same co-ords. see help set label
   via is now a required keyword for fit
   - fit f(x) 'file' ... via { 'file' | a,b,... }
   - this is to avoid confusing 'file' with 'using-format-string'
   win32 and 16-bit dos fixes
   - I can compile with tc++, but get an overlay error at runtime.
   new set of documentation programs (I haven't tried them)
   various tweaks to makefile
   changes to pslatex
   - substitute .ps at _last_ . in filename 
   - accept font size of enclosing document as an option.
   - dont forget to close aux file

in release 151

  linux security patch
  can specify font for labels, etc (postscript only ? - I haven't tried this)
  can specify linetype to draw grid / zeroaxes / arrows
  emx terminal driver
  first attempt at pipes for VMS and vector style - needs more work
  l/b/r/t-margin  in place of xmargin - more control over size of margins
  incompatible changes to polar mode:
  - t is now the dummy variable, so x is width of plot as expected
  - tics are not automatically on axes -   set {xy}tics axis nomirror
  - grid is not automatically polar - set grid x [mx] polar [angle]
  - no numbers on grid - they were always in degrees
  second axes
  - x2 and y2 are an independent pair of axes, but they inherit
    ranges from x and y if no second data
    - there can be problems with this, actually - if x2tics are not
      shown, x2range is not autoextended to whole number of tics, so
      same data might not have same range.
  - set x2tics/y2tics/x2label/y2label
  - set [no]log x2 / y2
  - plot [first,] f(x), 'file', ..., second, g(x), ...
  - get specify grid at any/all of x,y,x2,y2
  - see electron.dem
  set border <mask> - 12 bit binary number selects 12 sides of cube around splot
  can specify grid z, to get a grid on back wall of splot
  set mxtics [<interval>|default] | set nomxtics
  - set mxtics  gives auto for logscale, fixed for linear 
  binary, index and every keywords to datafiles.
  - every also works with binary files
  can use '-' as datafile for inline data (ends at line with e)
  can use '' to mean reuse previous file
  splot and fit now use datafile module
  - FIT_SKIP no longer supported - use fit f(x) 'file' every n
  can limit fit range using   fit [variable=min:max] f(variable) ...
  set ticscale <major> [<minor>]
  surface is clipped with no hidden line removal
  - still to do contour and hidden-line surface
  set {x|y|x2|y2} [axis|border] [no]mirror
  - can put tics on border or axes
  - mirror controls mirroring of tics on opposite axis
    - no longer coupled to  set tics out  setiing.
  No longer need to specify parametric mode for 3-column data files.
  ranges automatically extended to whole number of tic intervals
  - doesn't always manage to drop vertical from surface to corner of base
    - workaround is either specify range or use  set border

patchlevel 140
--------------
I've probably missed a lot of features since I'm so used to them.
Plus I never bothered with 3.5 so some of these may have been there.
some of these may have made it into the documentation
Here goes:

  fit f(x) 'file' via ...
  read and plot time data  (timedat.dem)
  set key [top|bottom|under] [left|right|out] [reverse] [box [<linetype>]]
  set key title 'text'
  Processing of escape sequences in "strings" but not 'strings'
  - TeX users in particular advised to use ''
  Multiline labels, etc, using "first\nsecond"
  enhpost driver
  call command (load with parameters)
  x error bars. splines. boxes. [some may have been in 3.5]
  pipes for amiga
  the using patch   plot 'file' using spec:spec:...
  - spec is either column number or (expression in $1, $2, ...)
  new pslatex driver with postscript to aux file.
  set pointsize <scale factor> on some terminals
  doubles in  plot...using  format string - %lf
  unlimited input line length and expression (action) table
  minor tic-marks (like logscale but also for linear)
  - also set grid [mx|my]



that's all I can think of for the moment...

   Q4.1: Does gnuplot have hidden line removal?
          Version 3.5 supports hidden line removal on all platforms
          except MS-DOS; use the command


        set hidden3d

   If someone can solve the 64K DGROUP memory problem, gnuplot would
          support hidden line removal on MS-DOS as well. Version 3.2
          supports limited hidden line removal.

   Q4.2: Does gnuplot support bar-charts/histograms/boxes?
          As of version 3.4, it does; use the style "with boxes" for bar
          charts. To get filled boxes, you can try a modification by
          Steve Cumming, available via ftp from
          ftp://grebe.geog.ubc.ca/pub/gnuplot as box.tar.

   Q4.3: Does gnuplot support multiple y-axes on a single plot?
          Yes, with two unofficial mods, multiplot.shar and borders.shar.
          They can be obtained from
          ftp://ftp.dartmouth.edu/pub/gnuplot/contrib/multi_woo.zip
          or ftp://ftp.cygnus.edu/incoming/gpx38.zip.

          Also, 3.6 supports this capability.

   Q4.4: Can I put multiple plots on a single page?
          Yes, with the multiplot.shar mod, or if you are running gnuplot
          3.6. If you are using PostScript output, check out mpage, which
          can be ftp'd from ftp.eng.umd.edu:pub/misc/mpage-2.tar.Z

   Q4.5: Can I put both data files and commands into a single file?
          This feature is in gnuplot 3.6.

   Q4.6: Can I put Greek letters and super/subscripts into my labels?
          You might try using the LaTeX terminal type and putting text
          like \alpha_{3} into it.

          David Denholm has written a PostScript terminal which allows
          for super/and subscripts, such as a^x or {/Symbol a }. Ftp to
          sotona.phys.soton.ac.uk [152.78.192.42] and get enhpost.trm,
          written by David Denholm and Matt Heffron. To install it,
          follow the instructions at the top of the file, then recompile.
          enhpost is also included in gnuplot 3.6.

   Q4.7: Can I do 1:1 scaling of axes?
          Not easily in 3.5; in 3.6, you can use "set size square".

   Q4.8: Can I put tic marks for x and y axes into 3d plots?
          In version 3.5, you can; use the "with boxes" option.

   Q4.9: Does gnuplot support a driver for <graphics format>?
          To see a list of the available graphic drivers for your
          installation of gnuplot, type "set term".

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

   Q4.10: Can I put different text sizes into my plots?
          If you use PostScript output, you can use Dave Denholm's and
          Matt Heffron's updated PostScript driver,
          /sotona.phys.soton.ac.uk:/enhpost.trm (see also Q4.6 ).
          Else, use 3.6.

   Q4.11 How do I modify gnuplot, and apply 'patches'?
          For this, you will need to recompile gnuplot.

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

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

   Q4.12 How do I skip data points?
          By specifying ? as a data value, as in


        1 2
        2 3
        3 ?
        4 5

   Q4.13 How do I plot every nth point?
          You can apply the patch point_skip from the contrib section
          (see Q5.3 or, assuming you have awk installed on your
          system, you can use the following line:


        gnuplot> plot "< awk '{if(NR%5==0)print}' file.dat"

   plots every 5th line, and

        gnuplot> plot "< awk '$0 !~ /^#/ {if(NR%40==0)print $1, $4}' file.dat"

   plots every 40th line while skipping commented lines.


  Section 5: Miscellaneous

   Q5.1: 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 wether you have an old version of gnuplot; if you do,
          chances are the bug has been fixed in a newer release.

          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 diff that fixes the problem, please e-email a
          report to bug-gnuplot@dartmouth.edu. The bug-gnuplot list is
          for reporting and collecting bug fixes, the
          comp.graphics.apps.gnuplot newsgroup will be more help for
          finding work arounds or actually solving gnuplot related
          problems. If you do send in a bug report, be sure and include
          the version of gnuplot (including patchlevel), terminal driver,
          operating system, an exact description of the bug and input
          which can reproduce the bug. Also, any context diffs should be
          referenced against the latest official version of gnuplot if at
          all possible.

   Q5.2: Can I use gnuplot routines for my own programs?
          Yes. John Campbell <jdc@nauvax.ucc.nau.edu> has written
          gplotlib, a version of gnuplot as C subroutines callable from a
          C program. This is available as gplotlib.tar.Z on the machine
          ftp.nau.edu in the directory /pub/gplotlib.tar.Z. This library
          has been updated to be compatible with version 3.5.

   Q5.3: What extensions have people made to gnuplot? Where can I get
          them?
          __Extensions are available from
          ftp://ftp.dartmouth.edu/pub/gnuplot/contrib/ . It contains
          the following files:

    Point Skips

          + _Data Filtering_ Instead of just having two params
            following the style param, there are now 4:
               o 1: line_type
               o 2: point_type
               o 3: point_skip - gives the number of data samples per
                 plotted point
               o 4: point_offs - gives the sample number on which to plot
                 the first point
            Thus points are plotted only for the samples n satisfying n =
            point_skip*i + point_offs for some non-negative integer i.
            From:
            pixar!sun!prony.Colorado.EDU!clarkmp@ucbvax.berkeley.edu
            (Michael Clark)
          + _Point Skip with Awk_ With UNIX,

gnuplot> plot "< awk '{if(NR%5==0)print$0}' file.dat"
        From: James Darrell McCauley, mccauley@ecn.purdue.edu
          + _New Xlib mods._ From: gregg hanna
            (gregor@kafka.saic.com)

    Vectors and Arrows
          + _Program to convert lines to vectors_ This program turns
            line segments into line segments with a half-arrow at the
            head: by uncommenting two lines below, the arrowhead will be
            a triangle. optional arguments: size angle where size is a
            fraction of each vector's magnitude and angle is in degrees
            all data taken from standard input, and output to standard
            output. typical invocation:

arrow 0.2 15 <vector.lin >vector.heads
        From: andrew@jarthur.claremont.edu (Andrew M. Ross)
          + _Vect2gp_, an awk script to make gnuplot command script
            to draw a vector field map. From: hiro@ice3.ori.u-tokyo.ac.jp
            (Yasu-Hiro YAMAZAKI)
          + _GNUPLOT to SIPP_ This is a "far from perfect" converter
            that takes gnuplot table output and splits it in polygons.
            Then it calls sipp to render it. You get sipp from
            isy.liu.se:/pub/sipp or ask archie. From:
            chammer@POST.uni-bielefeld.de (Carsten Hammer)

    Histograms and Pie Charts
          + _Histogram C program_ The short C program below is a
            filter that calculates a histogram from a sequence of numbers
            and prints the output in such a format that Gnuplot can plot
            the histogram by the command sequence

    !histogram < datain > tmp;
    plot "tmp" with impulses
            From: mustafa@seas.smu.edu (Mustafa Kocaturk)
          + _HG_ is an automatic histogram generator. it reads a
            column of data from an input file and emits a [log] histogram
            ks does ks or chi^2 tests on a set of input arrays. you need
            the "numerical recipes in C" library somewhere on your system
            to link this one. I can not undertake to fix bugs or add
            features, but I might do it if asked. From: Steve Cumming
            stevec@geog.ubc.ca
          + _Piechart C program_ The short C program below formats
            data for display as a piechart. From: mccauley@ecn.purdue.edu
            (James Darrell McCauley)

    Interprocess Communications
          + _Notes of Windows Hooks_ From: Maurice
            Castro,maurice@bruce.cs.monash.edu.au
          + _Named Pipes Example _From:
            dtaber@deathstar.risc.rockwell.com (Don Taber)
          + _PipeLib_ What the library does is set up to 20 programs
            going (like gnuplot), then allows you to send to them as if
            the program were typing on the command line. I've included a
            brief set of docs after the source code, in latex format.
            There is no facility to watch the output of a program. From:
            ssclift@neumann.uwaterloo.ca (Simon Clift)
          + _Popen example from lsqrfit_ The following function
            sends a command to gnuplot. Gnuplot will execute the command
            just as if you typed it at the gnuplot command line. This
            example is adapted from my least squares fitting program
            which is located at ftp.cdrom.com in
            pub/os2/2_x/unix/lsqrft14.zip. Complete source is included.
            From: michael@krypton.mit.edu (Michael Courtney)

    Multiple logical plots on a single page
          + _Gawk script for multiple encapsulated postscript on a
            page_ It's slightly more flexible than mpage, because it
            changes the aspect ratio of the plots; mpage according to the
            documentation only allows 1, 2, 4, or 8 plots on a page. This
            script works for unix with encapsulated postscript (eps)
            output. It should work with gawk or nawk, although I've only
            tested it with gawk. (Gawk is GNU's version of awk and is
            available from prep.ai.mit.edu.) You just specify how many
            rows and columns of plots you want and it does the rest. For
            example, gnuplot_eps rows=3 cols=2 *.eps | lpr will print all
            eps files in your current directory with 6 on a page. Also,
            see the comments in the file. From:
            holt@goethe.cns.caltech.edu (Gary Holt)
          + _Sed script for multiple encapsulated postscript on a
            page_ You have MULTIPLE postscript files each containing a
            single plot. From: wgchoe@scoupe.postech.ac.kr (Choe Won Gyu)
          + _Massive patch_ with add multiplotcapability to all
            devices and a lot more. The reason it is offered in this form
            is because the original multiplot.pat did not patch correctly
            into gnuplot version 3.5. This mod also add borders options,
            financial plots, multiple line titles and other asundry
            items. Use at your own risk. Look at the top of makefile.r
            for a more complete list of changes.
            From: Alex Woo, woo@playfair.stanford.edu

    lvs.zip
            This contains miscellaneous, modifications, which include:
          + Label positioning using either plot or device-relative
            coodinates
          + Portability to Irix-5.2 and Irix-5.3
          + The "thru" keyword has been extended to include "thrux" for
            the X - Coordinate
          + Capability to read a ordinary Fortran-style unformatted file
          + A Perl script for better handling of eps
          + Modifications to docs/doc2info to generate "next", "prev",
            and "up" data for each node.
          + Changes in the documentation to reflect the above.

    Miscellaneous Mods
          + _Congp3d3_ is a preprocessor to draw contour plots on
            irregular regions. From: mrb2@nrc.gov (Margaret Rose Byrne)
          + _Sockpipe_ is a socket based pipe needed for the
            Stardent OS. From: Mike Hallesy, Stardent Computer Product
            Support, hal@stardent.com
          + _Time Series_ is a patch to add multiline titles and
            labels, time series x and y data and tic marks, and automatic
            resizing of plots and much more. From: Hans Olav Eggestad,
            olav@jordforsk.nlh.no

    Other Operationing Systems
          + _MacIntosh Port of Version 3.2_ From: Noboru Yamamoto,
            sun!kekvax.kek.jp!YAMAMOTO@pixar.com
          + _MacIntosh Port of Version 3.5_ From:
            laval@londres.cma.fr (Philippe LAVAL)
          + _OS-9 Port of Version 3.2_


   Q5.4: Can I do heavy - duty data processing with 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 [132.206.9.13], and from the
          main Linux server, tsx-11.mit.edu [18.172.1.2] 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 goes
          together with gnuplot; it is called gnufit and is available
          from the official gnuplot sites, as the files gnufit12.info,
          gnufit12.tar.gz (source) and gft12dos.zip (MS-DOS). It has been
          merged into gnuplot 3.6.

          Michael Courtney has written a program called lsqrft, which
          uses the Levenberg - Marquardt - Algorithm for fitting data to
          a function. It is avialiable from ftp.cdrom.com as
          /pub/os2/2_x/unix/lsqrft13.zip; sources, which should compile
          on Unix, and executables for MS-DOS and OS/2 2.x are included.
          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
          [141.142.20.50] 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/~kgb/pgperl.html, the source is
          available from ftp://ftp.ast.cam.ac.uk/pub/kgb/pgperl/ or
          ftp://linux.nrao.edu/pub/packages/pgperl/.

          Another possibility is Octave. To quote from its README: Octave
          is a high-level language, primarily intended for numerical
          computations. It provides a convenient command line interface
          for solving linear and nonlinear problems numerically.

          The latest released version of Octave is always available via
          anonymous ftp from bevo.che.wisc.edu in the directory
          /pub/octave.

   Q5.5: I have ported gnuplot to another system, or patched it. What do
          I do?
          If your patch is small, mail it to bug-gnuplot@dartmouth.edu,
          with a thorough description of what the patch is supposed to
          do, which version of gnuplot it is relative to, etc. Also, you
          can send notification of the patch to the FAQ maintainer, if
          you want a mention. Please don't send the patch itself to me
          :-)

          If your modifications are extensive (such as a port to another
          system), upload your modifications to
          ftp://ftp.dartmouth.edu/pub/dropoff. Please drop a note to
          David.Kotz@dartmouth.edu, the maintainer of the gnuplot
          subdirectory there, plus a note to bug-gnuplot@dartmouth.edu.

   Q5.6: I want to help in developing gnuplot 3.6. What can I do?
          Join the gnuplot beta test mailing list by sending a mail
          containing the line


subscribe info-gnuplot-beta

   in the body (not the subject) of the mail to Majordomo@Dartmouth.EDU.


  Section 6: Making life easier

   Q6.1: How do I plot two functions in non - overlapping regions?
          Use a parametric plot. An example:


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

   Q6.2: 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"

   Unfortunately, in 3.2, there is a rather short limitation on the
          maximum argument length, so your command line may be truncated
          (usually, this will mean that awk cannot find the filename).
          Also, you may need to escape the $ - characters in your awk
          programs.

          As of version 3.4, gnuplot includes the thru - keyword for the
          plot command for running data files through a gnuplot - defined
          function.

          You can also get divhack.patch from
          sotona.phys.soton.ac.uk[152.78.192.42] via anonymous ftp. It
          allows expressions of the kind


        gnuplot> plot "datafile" using A:B:C

   where A,B,C,... are now either a column number, as usual, or an
          arbitrary expression enclosed in ()'s, and using $1,$2,etc to
          access the data columns.

   Q6.3: 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 [129.170.16.54, soon
          to be 129.170.8.11] 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.

   Q6.4: How do I save and restore my settings?
          Use the "save" and "load" commands for this; see "help save"
          and "help load" for details.

   Q6.5: 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.

   Q6.6: How do I plot a function f(x,y) which is bounded by other
          functions in the x-y plain?
          An example:


        f(x,y) = x**2 + y **2
        x(u) = 3*u
        yu(x) = x**2
        yl(x) = -x**2
        set parametric
        set cont
        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)

   Q6.7: How do I get rid of <feature in a plot>?
          Usually, there is a set command to do this; do a


        gnuplot> ?set no

   for a short overview.

   Q6.8: How do I call gnuplot from my own programs?
          Here's code which works for a UNIX system, using (efficient)
          named pipes.


#include <sys/types.h>
#include <sys/stat.h>
#include <stdlib.h>
#include <stdio.h>
#include <math.h>
#include <unistd.h>

#define PANIC(a) do { \
                perror(a); \
                if (temp_name) unlink(temp_name);\
                exit(1);\
        } while(0)

int main() {
    FILE *command,*data;
    char *temp_name = NULL;
    double a,b;
    int i;

    if ((temp_name = tmpnam((char *) 0)) == 0) PANIC("tmpnam failed");
    if(mkfifo(temp_name, S_IRUSR | S_IWUSR) != 0) PANIC("mkfifo failed");
    command = popen("gnuplot","w");
    fprintf(command,"plot \"%s\" with lines\n",temp_name); fflush(command);
    data = fopen(temp_name,"w");
    for (i=0; i<20; i++) {
        a = i/10.0;
        b = sin(a);
        fprintf(data,"%f %f\n",a,b);
    }
    fclose(data);
    fprintf(stderr,"press enter to continue..."); fflush(stderr);
    getchar();

    fprintf(command,"plot \"%s\" with lines\n",temp_name); fflush(command);
    data = fopen(temp_name,"w");
    for (i=0; i<20; i++) {
        a = i/10.0;
        b = cos(a);
        fprintf(data,"%f %f\n",a,b);
    }
    fclose(data);
    fprintf(stderr,"press enter to continue..."); fflush(stderr);
    getchar();
    pclose(command);
    unlink(temp_name);
    return 0;
}

   Here's code for OS/2, again using named pipes; I'm unable to check
          this out myself. This code is care of fearick@physci.uct.ac.za
          (Roger Fearick).


#include <stdio.h>
#define INCL_DOS
#define INCL_DOSPROCESS
#define INCL_DOSNMPIPES
#include <os2.h>

main()
    {
    HPIPE hpipe ;
    FILE *hfile, *hgnu ;
        /* create a named pipe. Use NP_WAIT so that DosConnect...
           blocks until client (gnuplot) opens, and client reads
           are blocked until data is available */
    DosCreateNPipe( "\\pipe\\gtemp",
                    &hpipe,
                    NP_ACCESS_OUTBOUND,
                    NP_WAIT|NP_TYPE_BYTE|1,
                    256,
                    256,
                    -1 ) ;
        /* use stream i/o */
    hfile = fdopen( hpipe, "w" ) ;

        /* start gnuplot; use unbuffered writes so we don't need to
           flush buffer after a command */
    hgnu = popen( "gnuplot", "w" ) ;
    setvbuf( hgnu, NULL, _IONBF, 0 ) ;

        /* plot a set of data */

    fprintf( hgnu, "plot '/pipe/gtemp'\n" ) ;  /* issue plot command */
    DosConnectNPipe( hpipe ) ;              /* wait until 'file' opened */
    fprintf( hfile, "1 1\n" ) ;             /* write data to 'file' */
    fprintf( hfile, "2 2\n" ) ;
    fprintf( hfile, "3 3\n" ) ;
    fprintf( hfile, "4 4\n" ) ;
    fflush( hfile ) ;                       /* flush buffer forces read */
    DosSleep( 500 ) ;                       /* allow gnuplot to catch up */
    DosDisConnectNPipe( hpipe ) ;           /* disconnect this session */
    fprintf( hgnu, "pause -1\n" ) ;         /* admire plot */

        /* plot another set of data */

    fprintf( hgnu, "plot '/pipe/gtemp'\n" ) ;
    DosConnectNPipe( hpipe ) ;
    fprintf( hfile, "1 4\n" ) ;
    fprintf( hfile, "2 3\n" ) ;
    fprintf( hfile, "3 2\n" ) ;
    fprintf( hfile, "4 1\n" ) ;
    fflush( hfile ) ;
    DosSleep( 500 ) ;
    DosDisConnectNPipe( hpipe ) ;
    fprintf( hgnu, "pause -1\n" ) ;

    DosClose( hpipe ) ;
    pclose( hgnu ) ;
    }

   ; The above code works for gnuplot 3.5. In gnuplot 3.6, this can be
          greatly simplified, since data can be fed 'inline, as in


plot '-' w l
1 1
2 3
3 4
e


  Section 7: Known problems

   Q7.1: Gnuplot is not plotting any points under X11! How come?
          Very probably, you still are using an old version of
          gnuplot_x11. Remove that, then do a full installation.

          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

        gnuplot> set term x11

   Q7.2: My isoline data generated by a Fortran program is not handled
          correctly. What can I do?
          One known cause for this is the use of list-directed output (as
          in WRITE(10,*) for generating blank lines. Fortran uses ASA
          carriage control characters, and for list - directed output
          this results in a space being output before the newline.
          Gnuplot does not like this. The solution is to generate blank
          lines using formatted output, as in WRITE(10,'()'). If you use
          carriage return files in VMS Fortran, you may have to open the
          file with OPEN(...,CARRIAGECONTROL='DTST') or convert it using
          the DECUS utility ATTRIB.EXE:


        VMS> ATTRIB/RATTRIB=IMPDTED FOR010.DAT

   Q7.3: 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,

        gnuplot> help set zero

   Q7.4: Gnuplot is plotting nothing when run via gnuplot <filename>!
          What can I do?
          Put a pause -1 after the plot command in the file.

   Q7.5: My formulas are giving me nonsense results! What's going on?
          Gnuplot does integer, and not floating point, arithmetic on
          integer expressions. For example, the expression 1/3 evaluates
          to zero. If you want floating point expressions, supply
          trailing dots for your floating point numbers. Example:


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

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

   Q7.6: My Linux gnuplot complains about a missing gnuplot_x11. What is
          wrong?
          The binary gnuplot distribution from sunsite.unc.edu and its
          mirrors in Linux/apps/math/gplotbin.tgz is missing one
          executable that is necessary to access the x11 terminal. Please
          install gnuplot from another Linux distribution, e.g.
          Slackware.

   Q7.7: set output 'filename' isn't outputting everything it should!
          You need to flush the output with a closing 'set output'.

  Section 8: Credits

   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; Axel Eble and Jutta Zimmermann helped with the
   conversion to HTML.



    Thomas Koenig, ig25@rz.uni-karlsruhe.de, 1994-03-28