Each terminal has a default set of arrow and point types, which can be seen by using the command test. arrow defines a set of arrow types and widths and point types and sizes so that you can refer to them later by an index instead of repeating all the information at each invocation.
Syntax:
set style arrow <index> default
set style arrow <index> {nohead | head | heads}
{size <length>,<angle>{,<backangle>}}
{filled | empty | nofilled}
{front | back}
{ {linestyle | ls <line_style>}
| {linetype | lt <line_type>}
{linewidth | lw <line_width} }
unset style arrow
show style arrow
<index> is an integer that identifies the arrowstyle.
If `default` is given all arrow style parameters are set to their default values.
If the linestyle <index> already exists, only the given parameters are changed while all others are preserved. If not, all undefined values are set to the default values.
Specifying `nohead` produces arrows drawn without a head—a line segment. This gives you yet another way to draw a line segment on the plot. By default, arrows have one head. Specifying `heads` draws arrow heads on both ends of the line.
Head size can be controlled by `size <length>,<angle>` or `size <length>,<angle>,<backangle>`, where `<length>` defines length of each branch of the arrow head and `<angle>` the angle (in degrees) they make with the arrow. `<Length>` is in x-axis units; this can be changed by `first`, `second`, `graph`, `screen`, or `character` before the <length>; see `coordinates` for details. `<Backangle>` only takes effect when `filled` or `empty` is also used. Then, `<backangle>` is the angle (in degrees) the back branches make with the arrow (in the same direction as `<angle>`). The `fig` terminal has a restricted backangle function. It supports three different angles. There are two thresholds: Below 70 degrees, the arrow head gets an indented back angle. Above 110 degrees, the arrow head has an acute back angle. Between these thresholds, the back line is straight.
Specifying `filled` produces filled arrow heads (if heads are used). Filling is supported on filled-polygon capable terminals, see help of pm3d for their list, otherwise the arrow heads are closed but not filled. The same result (closed but not filled arrow head) is reached by specifying `empty`. Further, filling and outline is obviously not supported on terminals drawing arrows by their own specific routines, like `metafont`, `metapost`, `latex` or `tgif`.
The line style may be selected from a user-defined list of line styles (see `set style line`) or may be defined here by providing values for `<line_type>` (an index from the default list of styles) and/or `<line_width>` (which is a multiplier for the default width).
Note, however, that if a user-defined line style has been selected, its properties (type and width) cannot be altered merely by issuing another arrow command with the appropriate index and `lt` or `lw`.
If `front` is given, the arrows are written on top of the graphed data. If `back` is given (the default), the arrow is written underneath the graphed data. Using `front` will prevent a arrow from being obscured by dense data.
Examples:
To draw an arrow without an arrow head and double width, use:
set style arrow 1 nohead lw 2
set arrow arrowstyle 1
See also arrow for further examples.