Usenet 1994 October/usenetsourcesnewsgroupsinfomagicoctober1994disk1.iso/answers/graphics/gnuplot-faq

Internet Message Format | 1993-12-19 | 28KB

Path: senator-bedfellow.mit.edu!bloom-beacon.mit.edu!xlink.net!rz.uni-karlsruhe.de!fg70.rz.uni-karlsruhe.de!ig25
From: [e-mail] (Koenig)
Newsgroups: comp.graphics.gnuplot,comp.answers,news.answers
Subject: comp.graphics.gnuplot FAQ (Frequent Answered Questions)
Supersedes: <[e-mail]>
Followup-To: comp.graphics.gnuplot
Date: 20 Dec 1993 03:23:11 GMT
Organization: University of Karlsruhe, Germany
Lines: 706
Approved: [e-mail]
Expires: 17 Jan 1994 03:23:03 GMT
Message-ID: <[e-mail]>
Reply-To: [e-mail]
NNTP-Posting-Host: fg70.rz.uni-karlsruhe.de
Mime-Version: 1.0
Content-Type: text/plain; charset=iso-8859-1
Content-Transfer-Encoding: 8bit
Summary: This is the FAQ (Frequently Answered Questions) list of the
         comp.graphics.gnuplot newsgroup, which discusses the
         gnuplot program for plotting 2D - and 3D - graphs.
Keywords: computer graphics, gnuplot
Xref: senator-bedfellow.mit.edu comp.graphics.gnuplot:2661 comp.answers:3088 news.answers:15990

Archive-name: graphics/gnuplot-faq
Version: $Header: comp-graphics-gnuplot,v 1.31 93/11/25 10:27:36 ig25 Exp $

This is the FAQ (Frequently Answered Questions) list of the
comp.graphics.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.gnuplot; quotations are believed to be in the public
domain.

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.

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>?

Section 4: Wanted features in gnuplot
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?

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?

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?

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?

Section 8: Credits

Questions and Answers:

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.gnuplot, comp.answers and news.answers.  Like many other
FAQ's, it is available via anonymous ftp from rtfm.mit.edu [18.70.0.209]
from the directory /pub/usenet/news.answers under the Archive-Name:  at
the top of the article, graphics/gnuplot-faq, and from the directory
/pub/usenet/comp.graphics.gnuplot, as well as via gopher from
gopher.univ-lyon1.fr [134.214.100.25].

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

Send comments, suggestions etc. via e-mail to Thomas Koenig,
[e-mail] or [e-mail].

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.

Q2.2: Where can I get gnuplot?

[This information may be dated, due to the release of gnuplot 3.5.
Please report any inaccuracies, if you find them.  Ed.]

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], the file is called /pub/gnuplot/gnuplot.3.5.tar.Z.
Official mirrors of that distribution are (for Australia)
monu1.cc.monash.edu.au [130.194.1.101] 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 pub/msdos/plot/gpt35*.zip, garbo.uwasa.fi
(Europe) [128.214.87.1] 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.

OS/2 2.x binaries are at ftp-os2.nmsu.edu [128.123.35.151], in
/os2/2.x/unix/gnu/gplt35.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 sonata.cc.purdue.edu and
cs.orst.edu.

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.

A version of gnuplot for the Macintosh is included in the gpcontrb
file, or can be found at wuarchive.wustl.edu [128.252.135.4], in
edu/math/mac/graphingAids, as MacGnuPlot3.2.sea.hqx and
MacGnuPlotPackage3.2.sea.hqx.

People without ftp access can use an ftp-mail server; send a message
saying 'help' to [e-mail] (for BITNET only) or to
[e-mail].

For a uuencoded copy of the the gnuplot sources (compressed tar file),
send this as the body of a message to [e-mail]:

        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 [e-mail] 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.

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 LIBS= line and run again.  If
you are making x11 on a sun, type 'make x11_sun'.

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


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.gnuplot or send mail to the gatewayed
mailing list [e-mail].  If you want to subscribe to
the mailing list, send mail to [e-mail],
but please don't do this if you can get comp.graphics.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 X - Windows.

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.


Section 4:  Wanted features in gnuplot

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.

Q4.3: Does gnuplot support multiple y-axes on a single plot?

No.

Q4.4: Can I put multiple plots on a single page?

Look at the rosendorf subdirectory in the gpcontrb distribution;
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?

Alex Woo has just put out an unofficial modification for beta test,
which does exactly this.  Otherwise, you might consider using Fudgit,
which can do it.

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.

If you use PostScript output, you might find something in the Green
subdirectory of the gpcontrb file (see Q5.3).

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 and get divpost34.trm.

Q4.7: Can I do 1:1 scaling of axes?

Not easily.

Q4.8: Can I put tic marks for x and y axes into 3d plots?

In version 3.5, you can.

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.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
[e-mail].  The bug-gnuplot list is for reporting and
collecting bug fixes, the comp.graphics.gnuplot mailing list 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 <[e-mail]> 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.  It is also included in the gpcontrb distribution
in the campbell subdirectory.

Q5.3: What extensions have people made to gnuplot?  Where can I get them?

[This is still hazy; please check this out and see whether it is correct.
Ed.]

Extensions have been put into the file gpcontrb.tar.Z, which is
available with the 3.5 release, from the same places you can
download the main distribution from.

Note that it has a size of 3.5 megabytes.

It contains the following subdirectories:

bigler subdirectory:
        From: [e-mail]
        Subject: Multiple plots from a Fortran program
budelsky subdirectory:
        From: [e-mail]
        Subject: This is the information file for porting gnuplot 3.2
                to OS-9/68000
byrne subdirectory:
        From: "Margaret R. Byrne" <[e-mail]>
        Subject: congp3d3 preprocessor to draw contour plots on
                irregular regions.
clark subdirectory:
        From: Michael Clark <[e-mail]>
        Subject: data filtering: adds point_skip & point_offs
clift subdirectory:
        From: [e-mail] (Simon Clift)
        Subject: Re: Running gnuplot from Fortran, (and C)
green subdirectory:
        From: Roque Donizete de Oliveira <[e-mail]>
        Subject: PostScript Greek symbols in gnuplot, new prologue
hanna subdirectory:
        From: [e-mail] (gregg hanna)
        Subject: x11-library mode, gnulib_x11.[c,h], xlibtest.c,makefile.xlib
klosowski subdirectory:
        From:   Carsten Steger <[e-mail]>
        Subject: New file "klein.dat"
        From: [e-mail] (Przemek Klosowski)
        Subject: calling gnuplot from Fortran
kocaturk subdirectory:
        From: [e-mail] (Mustafa Kocaturk)
        Subject: Histograms in gnuplot
richardson subdirectory:
        From: [e-mail] (Tony Richardson)
        Subject: Programmatic control of gnuplot from Unix
rosendorf subdirectory:
        From:  [e-mail]
        Subject: Multiple plots on a page
vanzandt subdirectory:
        From: James R. Van Zandt <[e-mail]>
        Subject: Spline generating program
white subdirectory:
        From: [e-mail]
        Subject: gnuplot 3.2 for Titan 3000
woo subdirectory:
        From: "Alex Woo" <[e-mail]>
        Subject: two additional title lines and fixes to errorbar style
yamamoto subdirectory:
        From: "NOBORU YAMAMOTO     " <sun!kekvax.kek.jp![e-mail]>
        Subject: Re: gnuplot on Apple Macintosh, "diff -c" of version 3.0
                (now includes binaries)
castro subdirectory:
        From: [e-mail] (Maurice Castro)
        Subject: Controlling gnuplot from another Windows program
grammes subdirectory:
        From: [e-mail] (Carsten Grammes)
        Subject: Nonlinear least squares fit mechanism
henke subdirectory:
        From: [e-mail] (Lars Hanke)
        Subject: Re: Changes to gnuplot 3.3b9
walton subdirectory:
        From: [e-mail] (Dave Walton)
        Subject: Inter Process Communication stuff

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 ([e-mail]).  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 ftp.uni-kl.de
[131.246.9.95] from the directory /pub/gnu/gnufit as gnufit10.tar.gz
or gft10dos.zip.

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.

Q5.5: I have ported gnuplot to another system, or patched it.  What do I do?

If your patch is small, mail it to [e-mail], with
a thorough description of what the patch is supposed to do, which version
of gnuplot it is relative to, etc.  Please don't mail it to the FAQ
maintainer.

If your modifications are extensive (such as a port to another system),
upload your modifications to dartmouth.edu:/pub/dropoff.  Please drop a
note to [e-mail], the maintainer of the gnuplot
subdirectory there, plus a note to [e-mail].


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 such as a short awk
program (use the "help plot datafile" command for an example).
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.

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] 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)

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.

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='LIST') or convert it using
the DECUS utility ATTRIB.EXE:

VMS> ATTRIB/RATTRIB=IMPLIED 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.

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.
--
Thomas Koenig, [e-mail], [e-mail]
The joy of engineering is to find a straight line on a double
logarithmic diagram.