\input texinfo @c -*-texinfo-*-

@c %**start of header

@setfilename gnuplot.info

@settitle Gnuplot: An Interactive Plotting Program

@setchapternewpage odd

@c %**end of header

@c define the command and options indeces

@defindex cm

@defindex op

@defindex tm

@dircategory Math

@direntry

* GNUPLOT: (gnuplot). An Interactive Plotting Program

@end direntry

@ifnottex

@node Top, gnuplot, (dir), (dir)

@top Master Menu

@end ifnottex

@example

GNUPLOT

An Interactive Plotting Program

Thomas Williams & Colin Kelley

Version 4.5 organized by:

Hans-Bernhard Broeker, Ethan A Merritt, and others

Copyright (C) 1986 - 1993, 1998, 2004 Thomas Williams, Colin Kelley

Copyright (C) 2004 - 2009 various authors

Mailing list for comments: gnuplot-info@@lists.sourceforge.net

Mailing list for bug reports: gnuplot-bugs@@lists.sourceforge.net

This manual was originally prepared by Dick Crawford

Version 4.5 - October 2009

Major contributors (alphabetic order):

@end example

@c ^ <h2> An Interactive Plotting Program </h2><p>

@c ^ <h2> Thomas Williams & Colin Kelley</h2><p>

@c ^ <h2> Version 4.4 organized by Ethan A Merritt and others</h2><p>

@c ^ <h2>Major contributors (alphabetic order):</h2>

@itemize @bullet

@item

Hans-Bernhard Broeker

@item

John Campbell

@item

Robert Cunningham

@item

David Denholm

@item

Gershon Elber

@item

Roger Fearick

@item

Carsten Grammes

@item

Lucas Hart

@item

Lars Hecking

@item

Thomas Koenig

@item

David Kotz

@item

Ed Kubaitis

@item

Russell Lang

@item

Alexander Lehmann

@item

Alexander Mai

@item

Ethan A Merritt

@item

Petr Mikulik

@item

Carsten Steger

@item

Tom Tkacik

@item

Jos Van der Woude

@item

Alex Woo

@item

James R. Van Zandt

@item

Johannes Zellner

@end itemize

@c ^<h2> Copyright (C) 1986 - 1993, 1998 - 2004 Thomas Williams, Colin Kelley<p>

@c ^ Mailing list for comments: gnuplot-info@@lists.sourceforge.net <p>

@c ^ Mailing list for bug reports: gnuplot-bugs@@lists.sourceforge.net <p>

@c ^</h2><p>

@c ^<h3> This manual was originally prepared by Dick Crawford</h3><p>

@c ^<h3> Last revised: March 2009</h3><p>

@c ^<hr>

@menu

* gnuplot::

* plotting_styles::

* Commands::

* Terminal_types::

* Graphical_User_Interfaces::

* Bugs::

* Concept_Index::

* Command_Index::

* Options_Index::

* Function_Index::

* Terminal_Index::

@end menu

@node gnuplot, plotting_styles, Top, Top

@chapter gnuplot

@menu

* Copyright::

* Introduction::

* Seeking-assistance::

* New_features_introduced_in_version_4.5::

* Backwards_compatibility::

* Batch/Interactive_Operation::

* Command-line-editing::

* Comments::

* Coordinates::

* Datastrings::

* Enhanced_text_mode::

* Environment::

* Expressions::

* Fonts::

* Glossary::

* linetypes::

* mouse_input::

* Plotting::

* Start-up::

* String_constants_and_string_variables::

* Substitution_and_Command_line_macros::

* Syntax::

* Time/Date_data::

@end menu

@node Copyright, Introduction, gnuplot, gnuplot

@section Copyright

@cindex copyright

@cindex license

@example

Copyright (C) 1986 - 1993, 1998, 2004, 2007 Thomas Williams, Colin Kelley

@end example

Permission to use, copy, and distribute this software and its

documentation for any purpose with or without fee is hereby granted,

provided that the above copyright notice appear in all copies and

that both that copyright notice and this permission notice appear

in supporting documentation.

Permission to modify the software is granted, but not the right to

distribute the complete modified source code. Modifications are to

be distributed as patches to the released version. Permission to

distribute binaries produced by compiling modified sources is granted,

provided you

@example

1. distribute the corresponding source modifications from the

released version in the form of a patch file along with the binaries,

2. add special version identification to distinguish your version

in addition to the base release version number,

3. provide your name and address as the primary contact for the

support of your modified version, and

4. retain our contact information in regard to use of the base

software.

@end example

Permission to distribute the released version of the source code along

with corresponding source modifications in the form of a patch file is

granted with same provisions 2 through 4 for binary distributions.

This software is provided "as is" without express or implied warranty

to the extent permitted by applicable law.

@example

AUTHORS

@end example

@example

Original Software:

Thomas Williams, Colin Kelley.

@end example

@example

Gnuplot 2.0 additions:

Russell Lang, Dave Kotz, John Campbell.

@end example

@example

Gnuplot 3.0 additions:

Gershon Elber and many others.

@end example

@example

Gnuplot 4.0 additions:

See list of contributors at head of this document.

@end example

@node Introduction, Seeking-assistance, Copyright, gnuplot

@section Introduction

@cindex introduction

@c ?

`Gnuplot` is a portable command-line driven graphing utility for Linux, OS/2,

MS Windows, OSX, VMS, and many other platforms. The source code is copyrighted

but freely distributed (i.e., you don't have to pay for it). It was originally

created to allow scientists and students to visualize mathematical functions

and data interactively, but has grown to support many non-interactive uses

such as web scripting. It is also used as a plotting engine by third-party

applications like Octave. Gnuplot has been supported and under active

development since 1986.

Gnuplot supports many types of plots in either 2D and 3D. It can draw using

lines, points, boxes, contours, vector fields, surfaces, and various

associated text. It also supports various specialized plot types.

Gnuplot supports many different types of output: interactive screen terminals

(with mouse and hotkey input), direct output to pen plotters or modern

printers, and output to many file formats (eps, fig, jpeg, LaTeX, metafont,

pbm, pdf, png, postscript, svg, ...). Gnuplot is easily extensible to include

new output modes. Recent additions include interactive terminals based on

aquaterm (OSX) and wxWidgets (multiple platforms).

The command language of `gnuplot` is case sensitive, i.e. commands and

function names written in lowercase are not the same as those written in

capitals. All command names may be abbreviated as long as the abbreviation is

not ambiguous. Any number of commands may appear on a line, separated by

semicolons (;). Strings may be set off by either single or double quotes,

although there are some subtle differences. See `syntax` and `quotes` for

more details. Examples:

@example

load "filename"

cd 'dir'

@end example

Many `gnuplot` commands have multiple options. Version 4 is less sensitive

to the order of these options than earlier versions, but some order-dependence

remains. If you see error messages about unrecognized options, please try

again using the exact order listed in the documentation.

Commands may extend over several input lines by ending each line but the last

with a backslash (\). The backslash must be the _last_ character on each

line. The effect is as if the backslash and newline were not there. That

is, no white space is implied, nor is a comment terminated. Therefore,

commenting out a continued line comments out the entire command

(see `comments`). But note that if an error occurs somewhere on a multi-line

command, the parser may not be able to locate precisely where the error is

and in that case will not necessarily point to the correct line.

In this document, curly braces (@{@}) denote optional arguments and a vertical

bar (|) separates mutually exclusive choices. `Gnuplot` keywords or @ref{help}

topics are indicated by backquotes or `boldface` (where available). Angle

brackets (<>) are used to mark replaceable tokens. In many cases, a default

value of the token will be taken for optional arguments if the token is

omitted, but these cases are not always denoted with braces around the angle

brackets.

For built-in help on any topic, type @ref{help} followed by the name of the topic

or `help ?` to get a menu of available topics.

The new `gnuplot` user should begin by reading about `plotting` (if in an

interactive session, type `help plotting`).

See the simple.dem demo, also available together with other demos on the web page

@uref{http://www.gnuplot.info/demo/,http://www.gnuplot.info/demo/

}

`Gnuplot` can be started from a command line or from an icon according to the

desktop environment. Running it from command line can take the syntax

@example

gnuplot @{OPTIONS@} file1 file2 ...

@end example

where file1, file2, etc. are input file as in the `load` command.

On X11-based systems, you can use

@example

gnuplot @{X11OPTIONS@} @{OPTIONS@} file1 file2 ...

@end example

see your X11 documentation or rather `x11` in this document.

Options interpreted by gnuplot may come anywhere on the line. Files are

executed in the order specified, as are commands supplied by the -e option,

for example

@example

gnuplot file1.in -e "reset" file2.in

@end example

The special filename "-" is used to force reading from stdin. `Gnuplot` exits

after the last file is processed. If no load files are named, `Gnuplot` takes

interactive input from stdin. See help `batch/interactive` for more details.

The options specific to gnuplot can be listed by typing

@example

gnuplot --help

@end example

See `command line options` for more details.

Hit 'h' for help about `hotkeys` and `mousing` features in interactive screen

terminals (`pm`, `windows`, `wxt`, `x11`).

Section `seeking-assistance` will help you to find further information, help

and FAQ.

@node Seeking-assistance, New_features_introduced_in_version_4.5, Introduction, gnuplot

@section Seeking-assistance

@cindex help-desk

@cindex seeking-assistance

@c ^ <a name="Seeking-assistance"></a>

The canonical gnuplot web page can be found at

@uref{http://www.gnuplot.info,http://www.gnuplot.info

}

Before seeking help, please check file FAQ.pdf or the above website for

@uref{http://www.gnuplot.info/faq/,FAQ (Frequently Asked Questions) list.

}

If you need help as a gnuplot user, please use the newsgroup

@example

comp.graphics.apps.gnuplot

@end example

We prefer that you read the messages through the newsgroup rather than

subscribing to the mailing list which is also available and carries the same

set of messages. Instructions for subscribing to gnuplot mailing lists may be

found via the gnuplot development website on SourceForge

@uref{http://sourceforge.net/projects/gnuplot,http://sourceforge.net/projects/gnuplot

}

The address for mailing to list members is:

@example

gnuplot-info@@lists.sourceforge.net

@end example

Bug reports and code contributions should be uploaded to the trackers at

@example

http://sourceforge.net/projects/gnuplot/support

@end example

Please check previous bug reports if the bug you want to report has not been

already fixed in a newer version of gnuplot.

The list of those interested in development version of gnuplot is:

@example

gnuplot-beta@@lists.sourceforge.net

@end example

When posting a question, please include full details of the version of

`gnuplot`, the machine, and operating system you are using. A _small_ script

demonstrating the problem may be useful. Function plots are preferable to

datafile plots. If email-ing to gnuplot-info, please state whether or not

you are subscribed to the list, so that users who use news will know to email

a reply to you. There is a form for such postings on the website.

@node New_features_introduced_in_version_4.5, Backwards_compatibility, Seeking-assistance, gnuplot

@section New features introduced in version 4.5

@cindex new-features

Gnuplot version 4.5 offers many new features introduced since the preceding

official version 4.4. This section lists major additions and gives a partial

list of changes and minor new features. For a more exhaustive list, see the

NEWS file.

@menu

* Canvas_size::

* New_plot_elements::

* New_or_revised_terminal_drivers::

* New_smoothing_algorithms::

@end menu

@node Canvas_size, New_plot_elements, New_features_introduced_in_version_4.5, New_features_introduced_in_version_4.5

@subsection Canvas size

@c ?canvas size

@cindex canvas

@c ?set term size

In earlier versions of gnuplot, some terminal types used the values from

@ref{size} to control also the size of the output canvas; others did not.

The use of 'set size' for this purpose was deprecated in version 4.2.

In version 4.4 almost all terminals now behave as follows:

`set term <terminal_type> size <XX>, <YY>` controls the size of the output

file, or "canvas". Please see individual terminal documentation for allowed

values of the size parameters. By default, the plot will fill this canvas.

`set size <XX>, <YY>` scales the plot itself relative to the size of the

canvas. Scale values less than 1 will cause the plot to not fill the entire

canvas. Scale values larger than 1 will cause only a portion of the plot to

fit on the canvas. Please be aware that setting scale values larger than 1

may cause problems on some terminal types.

The major exception to this convention is the PostScript driver, which

by default continues to act as it has in earlier versions. Be warned that

the next version of gnuplot may change the default behaviour of the

PostScript driver as well.

Example:

@example

set size 0.5, 0.5

set term png size 600, 400

set output "figure.png"

plot "data" with lines

@end example

These commands will produce an output file "figure.png" that is 600 pixels

wide and 400 pixels tall. The plot will fill the lower left quarter of this

canvas. This is consistent with the way multiplot mode has always worked,

however it is a change in the way the png driver worked for single plots in

version 4.0.

@node New_plot_elements, New_or_revised_terminal_drivers, Canvas_size, New_features_introduced_in_version_4.5

@subsection New plot elements

@cindex circles

@cindex ellipse

@cindex polygon

The @ref{object} command can now be used to define fixed circles, ellipses, and

polygons as well as rectangles. There are two corresponding new plot styles:

@ref{circles} and @ref{ellipses}.

See `circle`, `ellipse` and @ref{polygon}.

@node New_or_revised_terminal_drivers, New_smoothing_algorithms, New_plot_elements, New_features_introduced_in_version_4.5

@subsection New or revised terminal drivers

Two new drivers based on the cairo and pango libraries are included,

`pngcairo` and `pdfcairo`. These are alternatives to the older libgd-based

png driver and the older PDFLib-based pdf driver. The figures in the pdf

version of this manual were prepared using the pdfcairo terminal driver.

The `canvas` terminal driver produces javascript output that draws onto the

HTML canvas element of a web page. It can produce either a complete web page

containing a single plot, or a script that can be embedded as part of an

externally generated HTML document that perhaps contains multiple plots.

The embedded plots support browser-side mousing, including zoom/unzoom.

The `lua` terminal driver creates an data intended to be further processed

by a script in the lua programming language. At this point only one such

lua script, gnuplot-tikz.lua, is available. It produces a TeX document

suitable for use with the latex TikZ package. Other lua scripts could be

written to process the gnuplot output for use with other TeX packages,

or with other non-TeX tools.

`Set term tikz` is shorthand for `set term lua tikz`. As decribed above, it

uses the generic lua terminal and an external lua script to produce a latex

document.

@node New_smoothing_algorithms, , New_or_revised_terminal_drivers, New_features_introduced_in_version_4.5

@subsection New smoothing algorithms

@cindex kdensity

@cindex cumulative

New smoothing algorithms have been added for both 2- and 3-dimensional plots.

`smooth kdensity` and `smooth cumul` can be used with `plot` to draw

smooth histograms and cumulative distribution functions, resp. For use

with `splot` several new smoothing kernels have been added to @ref{dgrid3d}.

See @ref{smooth} @ref{dgrid3d}.

@node Backwards_compatibility, Batch/Interactive_Operation, New_features_introduced_in_version_4.5, gnuplot

@section Backwards compatibility

@c ?backwards compatibility

@cindex compatibility

Gnuplot version 4.0 deprecated certain syntax used in earlier versions, but

continued to recognize it. This is now under the control of a configuration

option, and can be disabled as follows:

@example

./configure --disable-backwards-compatibility

@end example

Notice: Deprecated syntax items may be disabled permanently in some future

version of gnuplot.

One major difference is the introduction of keywords to disambiguate complex

commands, particularly commands containing string variables. A notable issue

was the use of bare numbers to specify offsets, line and point types.

Illustrative examples:

Deprecated:

@example

set title "Old" 0,-1

set data linespoints

plot 1 2 4 # horizontal line at y=1

@end example

New:

@example

TITLE = "New"

set title TITLE offset char 0, char -1

set style data linespoints

plot 1 linetype 2 pointtype 4

@end example

@node Batch/Interactive_Operation, Command-line-editing, Backwards_compatibility, gnuplot

@section Batch/Interactive Operation

@cindex batch/interactive

@c ?command line options

`Gnuplot` may be executed in either batch or interactive modes, and the two

may even be mixed together on many systems.

Any command-line arguments are assumed to be either program options (first

character is -) or names of files containing `gnuplot` commands. The option

-e "command" may be used to force execution of a gnuplot command. Each file

or command string will be executed in the order specified. The special

filename "-" is indicates that commands are to be read from stdin.

`Gnuplot` exits after the last file is processed. If no load files and no

command strings are specified, `gnuplot` accepts interactive input from

stdin.

Both the @ref{exit} and @ref{quit} commands terminate the current command file and

`load` the next one, until all have been processed.

Examples:

To launch an interactive session:

@example

gnuplot

@end example

To launch a batch session using two command files "input1" and "input2":

@example

gnuplot input1 input2

@end example

To launch an interactive session after an initialization file "header" and

followed by another command file "trailer":

@example

gnuplot header - trailer

@end example

To give `gnuplot` commands directly in the command line, using the "-persist"

option so that the plot remains on the screen afterwards:

@example

gnuplot -persist -e "set title 'Sine curve'; plot sin(x)"

@end example

To set user-defined variables a and s prior to executing commands from a file:

@example

gnuplot -e "a=2; s='file.png'" input.gpl

@end example

@node Command-line-editing, Comments, Batch/Interactive_Operation, gnuplot

@section Command-line-editing

@cindex line-editing

@cindex editing

@cindex command-line-editing

Command-line editing and command history are supported using either an

external gnu readline library, an external BSD libedit library, or a

built-in equivalent. This choice is a configuration option at the time

gnuplot is built.

The editing commands of the built-in version are given below. The gnu

readline and BSD libedit libraries have their own documentation.

@example

`Line-editing`:

@end example

@example

^B moves back a single character.

^F moves forward a single character.

^A moves to the beginning of the line.

^E moves to the end of the line.

^H and DEL delete the previous character.

^D deletes the current character.

^K deletes from current position to the end of line.

^L,^R redraws line in case it gets trashed.

^U deletes the entire line.

^W deletes from the current word to the end of line.

@end example

@example

`History`:

@end example

@example

^P moves back through history.

^N moves forward through history.

@end example

@node Comments, Coordinates, Command-line-editing, gnuplot

@section Comments

@cindex comments

Comments are supported as follows: a `#` may appear in most places in a line

and `gnuplot` will ignore the rest of the line. It will not have this effect

inside quotes, inside numbers (including complex numbers), inside command

substitutions, etc. In short, it works anywhere it makes sense to work.

See also `set datafile commentschars` for specifying comment characters in

data files. Note that if a comment line ends in '\' then the subsequent

line is also treated as a comment.

@node Coordinates, Datastrings, Comments, gnuplot

@section Coordinates

@cindex coordinates

@cindex axes

The commands @ref{arrow}, `set key`, `set label` and @ref{object} allow you

to draw something at an arbitrary position on the graph. This position is

specified by the syntax:

@example

@{<system>@} <x>, @{<system>@} <y> @{,@{<system>@} <z>@}

@end example

Each <system> can either be `first`, `second`, `graph`, `screen`, or

`character`.

`first` places the x, y, or z coordinate in the system defined by the left

and bottom axes; `second` places it in the system defined by the second axes

(top and right); `graph` specifies the area within the axes---0,0 is bottom

left and 1,1 is top right (for splot, 0,0,0 is bottom left of plotting area;

use negative z to get to the base---see @ref{xyplane}); `screen`

specifies the screen area (the entire area---not just the portion selected by

@ref{size}), with 0,0 at bottom left and 1,1 at top right; and `character`

gives the position in character widths and heights from the bottom left of

the screen area (screen 0,0), `character` coordinates depend on the chosen

font size.

If the coordinate system for x is not specified, `first` is used. If the

system for y is not specified, the one used for x is adopted.

In some cases, the given coordinate is not an absolute position but a

relative value (e.g., the second position in @ref{arrow} ... `rto`). In

most cases, the given value serves as difference to the first position.

If the given coordinate resides in a logarithmic axis the value is

interpreted as factor. For example,

@example

set logscale x

set arrow 100,5 rto 10,2

@end example

plots an arrow from position 100,5 to position 1000,7 since the x axis is

logarithmic while the y axis is linear.

If one (or more) axis is timeseries, the appropriate coordinate should

be given as a quoted time string according to the @ref{timefmt} format string.

See @ref{xdata} and @ref{timefmt}. `Gnuplot` will also accept an integer

expression, which will be interpreted as seconds from 1 January 2000.

@node Datastrings, Enhanced_text_mode, Coordinates, gnuplot

@section Datastrings

@cindex datastrings

Data files may contain string data consisting of either an arbitrary string

of printable characters containing no whitespace or an arbitrary string of

characters, possibly including whitespace, delimited by double quotes.

The following sample line from a datafile is interpreted to contain four

columns, with a text field in column 3:

@example

1.000 2.000 "Third column is all of this text" 4.00

@end example

Text fields can be positioned within a 2-D or 3-D plot using the commands:

@example

plot 'datafile' using 1:2:4 with labels

splot 'datafile using 1:2:3:4 with labels

@end example

A column of text data can also be used to label the ticmarks along one or more

of the plot axes. The example below plots a line through a series of points

with (X,Y) coordinates taken from columns 3 and 4 of the input datafile.

However, rather than generating regularly spaced tics along the x axis

labeled numerically, gnuplot will position a tic mark along the x axis at the

X coordinate of each point and label the tic mark with text taken from column

1 of the input datafile.

@example

set xtics

plot 'datafile' using 3:4:xticlabels(1) with linespoints

@end example

@cindex columnheader

There is also an option that will interpret the first entry in a column of

input data (i.e. the column heading) as a text field, and use it as the key

title for data plotted from that column. The example given below will use the

first entry in column 2 to generate a title in the key box, while processing

the remainder of columns 2 and 4 to draw the required line:

@example

plot 'datafile' using 1:(f($2)/$4) with lines title columnhead(2)

@end example

See @ref{labels}, `using xticlabels`, @ref{title}, @ref{using}.

@node Enhanced_text_mode, Environment, Datastrings, gnuplot

@section Enhanced text mode

@c ?enhanced text

@cindex enhanced

Many terminal types support an enhanced text mode in which additional

formatting information is embedded in the text string. For example, "x^2"

will write x-squared as we are used to seeing it, with a superscript 2.

This mode is normally selected when you set the terminal, e.g.

"set term png enhanced", but may also be toggled afterward using

"set termoption enhanced", or by marking individual strings as in

"set label 'x_2' noenhanced".

@example

Control Examples Explanation

^ a^x superscript

_ a_x subscript

@@ @@x or a@@^b_@{cd@} phantom box (occupies no width)

& &@{space@} inserts space of specified length

~ ~a@{.8-@} overprints '-' on 'a', raised by .8

times the current fontsize

@end example

Braces can be used to place multiple-character text where a single character

is expected (e.g., 2^@{10@}). To change the font and/or size, use the full form:

@{/[fontname][=fontsize | *fontscale] text@}. Thus @{/Symbol=20 G@} is a 20 pt

GAMMA and @{/*0.75 K@} is a K at three-quarters of whatever fontsize is currently

in effect. (The '/' character MUST be the first character after the '@{'.)

The phantom box is useful for a@@^b_c to align superscripts and subscripts

but does not work well for overwriting an accent on a letter. For the latter,

it is much better to use an encoding (e.g. iso_8859_1 or utf8) that contains

a large variety of letters with accents or other diacritical marks. See

@ref{encoding}. Since the box is non-spacing, it is sensible to put the shorter

of the subscript or superscript in the box (that is, after the @@).

Space equal in length to a string can be inserted using the '&' character.

Thus

@example

'abc&@{def@}ghi'

@end example

would produce

@example

'abc ghi'.

@end example

The '~' character causes the next character or bracketed text to be

overprinted by the following character or bracketed text. The second text

will be horizontally centered on the first. Thus '~a/' will result in an 'a'

with a slash through it. You can also shift the second text vertically by

preceding the second text with a number, which will define the fraction of the

current fontsize by which the text will be raised or lowered. In this case

the number and text must be enclosed in brackets because more than one

character is necessary. If the overprinted text begins with a number, put a

space between the vertical offset and the text ('~@{abc@}@{.5 000@}'); otherwise

no space is needed ('~@{abc@}@{.5---@}'). You can change the font for one or

both strings ('~a@{.5 /*.2 o@}'---an 'a' with a one-fifth-size 'o' on top---and

the space between the number and the slash is necessary), but you can't

change it after the beginning of the string. Neither can you use any other

special syntax within either string. You can, of course, use control

characters by escaping them (see below), such as '~a@{\^@}'

You can access special symbols numerically by specifying \character-code (in

octal), e.g., @{/Symbol \245@} is the symbol for infinity. This does not work

for multibyte encodings like UTF-8, however. In a UTF-8 environment, you

should be able to enter multibyte sequences implicitly by typing or otherwise

selecting the character you want.

You can escape control characters using \, e.g., \\, \@{, and so on.

But be aware that strings in double-quotes are parsed differently than those

enclosed in single-quotes. The major difference is that backslashes may need

to be doubled when in double-quoted strings.

Examples (these are hard to describe in words---try them!):

@example

set xlabel 'Time (10^6 @{/Symbol m@}s)'

set title '@{/Symbol=18 \\362@@_@{/=9.6 0@}^@{/=12 x@}@} \\

@{/Helvetica e^@{-@{/Symbol m@}^2/2@} d@}@{/Symbol m@}'

@end example

The file "ps_guide.ps" in the /docs/psdoc subdirectory of the gnuplot source

distribution contains more examples of the enhanced syntax.

@node Environment, Expressions, Enhanced_text_mode, gnuplot

@section Environment

@cindex environment

A number of shell environment variables are understood by `gnuplot`. None of

these are required, but may be useful.

If GNUTERM is defined, it is used as the name of the terminal type to be

used. This overrides any terminal type sensed by `gnuplot` on start-up, but

is itself overridden by the .gnuplot (or equivalent) start-up file

(see `start-up`) and, of course, by later explicit changes.

GNUHELP may be defined to be the pathname of the HELP file (gnuplot.gih).

On VMS, the logical name GNUPLOT$HELP should be defined as the name of the

help library for `gnuplot`. The `gnuplot` help can be put inside any system

help library, allowing access to help from both within and outside `gnuplot`

if desired.

On Unix, HOME is used as the name of a directory to search for a .gnuplot

file if none is found in the current directory. On MS-DOS, Windows and OS/2,

GNUPLOT is used. On Windows, the NT-specific variable USERPROFILE is also

tried. VMS, SYS$LOGIN: is used. Type `help start-up`.

On Unix, PAGER is used as an output filter for help messages.

On Unix, SHELL is used for the @ref{shell} command. On MS-DOS and OS/2, COMSPEC

is used for the @ref{shell} command.

FIT_SCRIPT may be used to specify a `gnuplot` command to be executed when a

fit is interrupted---see @ref{fit}. FIT_LOG specifies the default filename of the

logfile maintained by fit.

GNUPLOT_LIB may be used to define additional search directories for data

and command files. The variable may contain a single directory name, or

a list of directories separated by a platform-specific path separator,

eg. ':' on Unix, or ';' on DOS/Windows/OS/2 platforms. The contents

of GNUPLOT_LIB are appended to the @ref{loadpath} variable, but not saved

with the @ref{save} and `save set` commands.

Several gnuplot terminal drivers access TrueType fonts via the gd library.

For these drivers the font search path is controlled by the environmental

variable GDFONTPATH. Furthermore, a default font for these drivers may be

set via the environmental variable GNUPLOT_DEFAULT_GDFONT.

The postscript terminal uses its own font search path. It is controlled by

the environmental variable GNUPLOT_FONTPATH. The format is the same as for

GNUPLOT_LIB. The contents of GNUPLOT_FONTPATH are appended to the @ref{fontpath}

variable, but not saved with the @ref{save} and `save set` commands.

GNUPLOT_PS_DIR is used by the postscript driver to search for external

prologue files. Depending on the build process, gnuplot contains either a

built-in copy of those files or a default hardcoded path. You can use this

variable have the postscript terminal use custom prologue files rather than

the default files. See `postscript prologue`.

@node Expressions, Fonts, Environment, gnuplot

@section Expressions

@cindex expressions

In general, any mathematical expression accepted by C, FORTRAN, Pascal, or

BASIC is valid. The precedence of these operators is determined by the

specifications of the C programming language. White space (spaces and tabs)

is ignored inside expressions.

Complex constants are expressed as @{<real>,<imag>@}, where <real> and <imag>

must be numerical constants. For example, @{3,2@} represents 3 + 2i; @{0,1@}

represents 'i' itself. The curly braces are explicitly required here.

@cindex division

Note that gnuplot uses both "real" and "integer" arithmetic, like FORTRAN and

C. Integers are entered as "1", "-10", etc; reals as "1.0", "-10.0", "1e1",

3.5e-1, etc. The most important difference between the two forms is in

division: division of integers truncates: 5/2 = 2; division of reals does

not: 5.0/2.0 = 2.5. In mixed expressions, integers are "promoted" to reals

before evaluation: 5/2e0 = 2.5. The result of division of a negative integer

by a positive one may vary among compilers. Try a test like "print -5/2" to

determine if your system chooses -2 or -3 as the answer.

The integer expression "1/0" may be used to generate an "undefined" flag,

which causes a point to ignored; the `ternary` operator gives an example.

Or you can use the pre-defined variable NaN to achieve the same result.

@cindex NaN

The real and imaginary parts of complex expressions are always real, whatever

the form in which they are entered: in @{3,2@} the "3" and "2" are reals, not

integers.

Gnuplot can also perform simple operations on strings and string variables.

For example, the expression ("A" . "B" eq "AB") evaluates as true, illustrating

the string concatenation operator and the string equality operator.

A string which contains a numerical value is promoted to the corresponding

integer or real value if used in a numerical expression. Thus ("3" + "4" == 7)

and (6.78 == "6.78") both evaluate to true. An integer, but not a real or

complex value, is promoted to a string if used in string concatenation.

A typical case is the use of integers to construct file names or other strings;

e.g. ("file" . 4 eq "file4") is true.

Substrings can be specified using a postfixed range descriptor [beg:end].

For example, "ABCDEF"[3:4] == "CD" and "ABCDEF"[4:*] == "DEF"

The syntax "string"[beg:end] is exactly equivalent to calling the built-in

string-valued function substr("string",beg,end), except that you cannot

omit either beg or end from the function call.

@menu

* Functions::

* Operators::

* Gnuplot-defined_variables::

* User-defined_variables_and_functions::

@end menu

@node Functions, Operators, Expressions, Expressions

@subsection Functions

@c ?expressions functions

@cindex functions

@opindex functions

The functions in `gnuplot` are the same as the corresponding functions in

the Unix math library, except that all functions accept integer, real, and

complex arguments, unless otherwise noted.

For those functions that accept or return angles that may be given in either

degrees or radians (sin(x), cos(x), tan(x), asin(x), acos(x), atan(x),

atan2(x) and arg(z)), the unit may be selected by @ref{angles}, which

defaults to radians.

@menu

* abs::

* acos::

* acosh::