![[ternary.gif]](http://www.gnuplot.info/doc/ternary.gif)
Note that `gnuplot` quietly ignores undefined values, so the final branch of
the function (1/0) will produce no plottable points. Note also that f(x)
will be plotted as a continuous function across the discontinuity if a line
style is used. To plot it discontinuously, create separate functions for the
two pieces. (Parametric functions are also useful for this purpose.)
For data in a file, plot the average of the data in columns 2 and 3 against
the datum in column 1, but only if the datum in column 4 is non-negative:
@example
plot 'file' using 1:( $4<0 ? 1/0 : ($2+$3)/2 )
@end example
For an explanation of the @ref{using} syntax, please see @ref{using}.
@node Gnuplot-defined_variables, User-defined_variables_and_functions, Operators, Expressions
@subsection Gnuplot-defined variables
@c ?gnuplot-defined variables
Gnuplot maintains a number of read-only variables that reflect the current
internal state of the program and the most recent plot. These variables begin
with the prefix "GPVAL_".
Examples include GPVAL_TERM, GPVAL_X_MIN, GPVAL_X_MAX, GPVAL_Y_MIN.
Type `show variables all` to display the complete list and current values.
Values related to axes parameters (ranges, log base) are values used during the
last plot, not those currently `set`.
@cindex errors
@cindex error state
The read-only variable GPVAL_ERRNO is set to a non-zero value if any gnuplot
command terminates early due to an error. The most recent error message is
stored in the string variable GPVAL_ERRMSG. Both GPVAL_ERRNO and GPVAL_ERRMSG
can be cleared using the command `reset errors`.
Interactive terminals with `mouse` functionality maintain read-only variables
with the prefix "MOUSE_". See @ref{variables} for details.
The @ref{fit} mechanism uses several variables with names that begin "FIT_". It
is safest to avoid using such names. "FIT_LIMIT", however, is one that you
may wish to redefine. Under `set fit errorvariables`, the error for each
fitted parameter will be stored in a variable named like the parameter, but
with "_err" appended. See the documentation on @ref{fit} for details.
See @ref{variables}, `reset errors`, @ref{variables}, and @ref{fit}.
@node User-defined_variables_and_functions, , Gnuplot-defined_variables, Expressions
@subsection User-defined variables and functions
@c ?expressions user-defined
@c ?user-defined variables
@cindex user-defined
@cindex variables
@opindex variables
New user-defined variables and functions of one through five variables may
be declared and used anywhere, including on the `plot` command itself.
User-defined function syntax:
@example
![[userdefined.gif]](http://www.gnuplot.info/doc/userdefined.gif)
The final two examples illustrate a user-defined string variable and a
user-defined string function.
@cindex NaN
@cindex pi
Note that the variables `pi` (3.14159...) and `NaN` (IEEE "Not a Number") are
already defined. You can redefine these to something else if you really need
to. The original values can be recovered by setting:
@example
NaN = GPVAL_NaN
pi = GPVAL_pi
@end example
Other variables may be defined under various gnuplot operations like mousing in
interactive terminals or fitting; see @ref{variables} for details.
You can check for existence of a given variable V by the exists("V")
expression. For example
@example
a = 10
if (exists("a")) print "a is defined"
if (!exists("b")) print "b is not defined"
@end example
Valid names are the same as in most programming languages: they must begin
with a letter, but subsequent characters may be letters, digits, "$", or "_".
See @ref{functions}, @ref{functions}, @ref{variables}, @ref{macros}.
@node Glossary, linetype, Expressions, gnuplot
@section Glossary
@cindex glossary
Throughout this document an attempt has been made to maintain consistency of
nomenclature. This cannot be wholly successful because as `gnuplot` has
evolved over time, certain command and keyword names have been adopted that
preclude such perfection. This section contains explanations of the way
some of these terms are used.
A "page" or "screen" or "canvas" is the entire area addressable by `gnuplot`.
On a desktop it is a full window; on a plotter, it is a single sheet of paper;
in svga mode it is the full monitor screen.
A screen may contain one or more "plots". A plot is defined by an abscissa
and an ordinate, although these need not actually appear on it, as well as
the margins and any text written therein.
A plot contains one "graph". A graph is defined by an abscissa and an
ordinate, although these need not actually appear on it.
A graph may contain one or more "lines". A line is a single function or
data set. "Line" is also a plotting style. The word will also be used in
sense "a line of text". Presumably the context will remove any ambiguity.
The lines on a graph may have individual names. These may be listed
together with a sample of the plotting style used to represent them in
the "key", sometimes also called the "legend".
The word "title" occurs with multiple meanings in `gnuplot`. In this
document, it will always be preceded by the adjective "plot", "line", or
"key" to differentiate among them.
A 2D graph may have up to four labelled @ref{axes}. The names of the four axes
are "x" for the axis along the bottom border of the plot, "y" for the axis
along the left border, "x2" for the top border, and "y2" for the right border.
See @ref{axes}.
A 3D graph may have up to three labelled @ref{axes} -- "x", "y" and "z". It is
not possible to say where on the graph any particular axis will fall because
you can change the direction from which the graph is seen with @ref{view}.
When discussing data files, the term "record" will be resurrected and used
to denote a single line of text in the file, that is, the characters between
newline or end-of-record characters. A "point" is the datum extracted from
a single record. A "datablock" is a set of points from consecutive records,
delimited by blank records. A line, when referred to in the context of a
data file, is a subset of a datablock.
@node linetype, mouse_input, Glossary, gnuplot
@section linetype, colors, and styles
@cindex linetype
@cindex colors
Each gnuplot terminal type provides a set of distinct "linetypes". These may
differ in color, in thickness, in dot/dash pattern, or in some combination of
color and dot/dash. The default linetypes for a particular terminal can be
previewed by issuing the @ref{test} command after setting the terminal type.
The pre-defined colors and dot/dash patterns are not guaranteed to be
consistent for all terminal types, but all terminals use the special linetype
-1 to mean a solid line in the primary foreground color (normally black).
By default, successive functions or datafiles plotted by a single command will
be assigned successive linetypes. You can override this default by specifying
a particular linetype for any function, datafile, or plot element.
Examples:
@example
plot "foo", "bar" # plot two files using linetypes 1, 2
plot sin(x) linetype 4 # terminal-specific linetype color 4
plot sin(x) lt -1 # black
@end example
@cindex colors
For many terminal types it is also possible to assign user-defined colors
using explicit rgb (red, green, blue) values, named colors, or color values
that refer to the current PM3D palette.
Examples:
@example
plot sin(x) lt rgb "violet" # one of gnuplot's named colors
plot sin(x) lt rgb "#FF00FF" # explicit RGB triple in hexadecimal
plot sin(x) lt palette cb -45 # whatever color corresponds to -45
# in the current cbrange of the palette
plot sin(x) lt palette frac 0.3 # fractional value along the palette
@end example
See @ref{colornames}, @ref{palette}, @ref{cbrange}.
For terminals that support dot/dash patterns, each default linetype has both
a dot-dash pattern and a default color. However, you can override the default
color by using the keyword `linecolor`, abbreviated `lc`. For example, the
postscript terminal provides a dashed blue line as linetype 3. The plot
commands below use this same dash pattern for three plots, one in blue (the
default), another in red (the default for linetype 1), and a third in gold.
Example:
@example
set term postscript dashed color
plot 'foo' lt 3, 'baz' lt 3 linecolor 1, 'bar' lt 3 lc rgb 'gold'
@end example
Lines can have additional properties such as linewidth. You can associate
these various properties, as well as equivalent properties for point symbols,
into user-defined "line styles" using the command `set style line`. Once
you have defined a linestyle, you can use it in a plot command to control
the appearance of one or more plot elements.
Examples:
@example
# define a new line style with terminal-independent color cyan,
# linewidth 3, and associated point type 6 (a circle with a dot in it).
set style line 5 lt rgb "cyan" lw 3 pt 6
plot sin(x) with linespoints ls 5 # user-defined line style 5
@end example
See `linestyle`, `set style line`.
@menu
* colorspec::
@end menu
@node colorspec, , linetype, linetype
@subsection colorspec
@cindex colorspec
@cindex rgbcolor
@cindex colors
@cindex lc
@cindex linecolor
@cindex tc
@cindex textcolor
Many commands allow you to specify a linetype with an explicit color.
Terminal-independent color choice is only possible for terminals that support
RGB color or pm3d palettes.
Syntax:
@example
... @{linecolor | lc@}