11.52.4 axis

set axis <axis> [ ( visible | invisible ) ]
  [ ( top | bottom | left | right | front | back ) ]
  [ ( atzero | notatzero ) ]
  [ ( automirrored | mirrored | fullmirrored ) ]
  [ ( noarrow | arrow | reversearrow | twowayarrow ) ]
  [ linked [ item <number> ] <axis> [ using <expression> ] ]

The set axis command is used to add additional axes to plots and to configure their appearance. Where an axis is stated on its own, as in the example

set axis x2

additional horizontal or vertical axes are added with default settings. The converse statements

set noaxis x2
unset axis x2

are used, respectively, to remove axes from plots and to return them to their default configurations, which often has the same effect of removing them from the graph, unless they are configured otherwise in a configuration file.

The position of any axis can be explicitly set using syntax of the form:

set axis x top
set axis y right
set axis z back

Horizontal axes can be set to appear either at the top or bottom; vertical axes can be set to appear either at the left or right; and -axes can be set to appear either at the front or back. By default, the x1-axis is placed along the bottom of graphs and the y1-axis is placed up the left-hand side of graphs. On three-dimensional plots, the z1-axis is placed at the front of the graph. The second set of axes are placed opposite to the first: the x2-, y2- and z2-axes are placed respectively along the top, right and back sides of graphs. Higher-numbered axes are placed alongside the x1-, y1- and z1-axes.

The following keywords may also be placed alongside the positional keywords listed above to specify how the axis should appear:

• arrow – Specifies that an arrowhead should be drawn on the right/top end of the axis. [Not default].

• atzero – Specifies that rather than being placed along an edge of the plot, the axis should mark the lines where the perpendicular axes x1, y1 and/or z1 are zero. [Not default].

• automirrored – Specifies that an automatic decision should be made between the behaviour of mirrored and nomirrored. If there are no axes on the opposite side of the graph, a mirror axis is produced. If there are already axes on the opposite side of the graph, no mirror axis is produced. [Default].

• fullmirrored – Similar to mirrored. Specifies that this axis should have a corresponding twin placed on the opposite side of the graph with mirroring ticks and labelling. [Not default; see automirrored].

• invisible – Specifies that the axis should not be drawn; data can still be plotted against it, but the axis is unseen. See Example 8.11.2 for a plot where all of the axes are invisible.

• linked – Specifies that the axis should be linked to another axis; see Section 8.8.9.

• mirrored – Specifies that this axis should have a corresponding twin placed on the opposite side of the graph with mirroring ticks but with no labels on the ticks. [Not default; see automirrored].

• noarrow – Specifies that no arrowheads should be drawn on the ends of the axis. [Default].

• nomirrored – Specifies that this axis should not have any corresponding twins. [Not default; see automirrored].

• notatzero – Opposite of atzero; the axis should be placed along an edge of the plot. [Default].

• notlinked – Specifies that the axis should no longer be linked to any other; see Section 8.8.9. [Default].

• reversearrow – Specifies that an arrowhead should be drawn on the left/bottom end of the axis. [Not default].

• twowayarrow – Specifies that arrowheads should be drawn on both ends of the axis. [Not default].

• visible – Specifies that the axis should be displayed; opposite of invisible. [Default].