Basic usage

The main purpose of the Gnuplot.jl package is to send data and commands to the underlying gnuplot process, in order to generate plots. Unlike other packages, however, the actual commands to plot, or the plot attributes, are not specified through function calls. This is what makes Gnuplot.jl easy to learn and use: there are no functions or keywords names to memorize^[1].

The most important symbols exported by the package are the @gp (for 2D plots) and @gsp (for 3D plots) macros, both accepting any number of arguments, and whose meaning is interpreted as follows:

• one, or a group of consecutive, array(s) build up a dataset. The different arrays are accessible as columns 1, 2, etc. from the gnuplot process. The number of required input arrays depends on the chosen plot style (see gnuplot documentation);

• a string occurring before a dataset is interpreted as a gnuplot command (e.g. set grid);

• a string occurring immediately after a dataset is interpreted as a plot element for the dataset, by which you can specify using clause, with clause, line styles, etc.;

• the special symbol :-, whose meaning is to avoid starting a new plot (if given as first argument), or to avoid immediately running all commands to create the final plot (if given as last argument). Its purpose is to allow splitting one long statement into multiple (shorter) ones.

The above list shows all the fundamental concepts to follow the examples presented below. The @gp and @gsp macros also accepts further arguments, but their use will be discussed in Advanced usage.

2D plots

Here we will show a few examples to generate 2D plots. The examples are intentionally very simple to highlight the behavior of Gnuplot.jl. See Examples for more complex ones.

Remember to run:

using Gnuplot

before running the examples.

Simple examples involving just gnuplot commands:

Plot a sinusoid:

@gp "plot sin(x)"

Plot two curves:

@gp "set key left" "plot sin(x)" "pl cos(x)"

Split a @gp call in three statements:

@gp    "set grid"  :-
@gp :- "p sin(x)"  :-
@gp :- "plo cos(x)"

Send data from Julia to gnuplot:

Plot a parabola

@gp (1:20).^2

Plot a parabola with scaled x axis, lines and legend

x = 1:20
@gp "set key left"   x ./ 20   x.^2   "with lines tit 'Parabola'"

Multiple datasets, logarithmic axis, labels and colors, etc.

x = 1:0.1:10
@gp    "set grid" "set key left" "set logscale y"
@gp :- "set title 'Plot title'" "set label 'X label'" "set xrange [0:*]"
@gp :- x x.^0.5 "w l tit 'Pow 0.5' dt 2 lw 2 lc rgb 'red'"
@gp :- x x      "w l tit 'Pow 1'   dt 1 lw 3 lc rgb 'blue'"
@gp :- x x.^2   "w l tit 'Pow 2'   dt 3 lw 2 lc rgb 'purple'"

Keywords for common commands

In order to avoid typing long, and very frequently used gnuplot commands, Gnuplot.jl provides a few keywords which can be used in both @gp and @sgp calls:

• xrange=[low, high] => "set xrange [low:high];
• yrange=[low, high] => "set yrange [low:high];
• zrange=[low, high] => "set zrange [low:high];
• cbrange=[low, high]=> "set cbrange[low:high];
• key="..." => "set key ...";
• title="..." => "set title \"...\"";
• xlabel="..." => "set xlabel \"...\"";
• ylabel="..." => "set ylabel \"...\"";
• zlabel="..." => "set zlabel \"...\"";
• cblabel="..." => "set cblabel \"...\"";
• xlog=true => set logscale x;
• ylog=true => set logscale y;
• zlog=true => set logscale z;

All such keywords can be abbreviated to unambiguous names.

By using the above keywords the first lines of the previous example:

@gp    "set grid" "set key left" "set logscale y"
@gp :- "set title 'Plot title'" "set label 'X label'" "set xrange [0:*]"

can be replaced with a shorter version:

@gp    "set grid" k="left" ylog=true
@gp :- tit="Plot title" xlab="X label" xr=[0,NaN]

where NaN in the xrange keyword means using axis autoscaling.

Plot images

Gnuplot.jl can also display images, i.e. 2D arrays:

img = randn(Float64, 30, 50)
img[10,:] .= -5
@gp img "w image notit"

Note that the first index in the img matrix corresponds to the x coordinate when the image is displayed.

If the orientation is not the correct one you may adjust it with the gnuplot rotate= keyword (the following example requires the TestImages package to be installed):

using TestImages
img = testimage("lighthouse");
@gp "set size square" "set autoscale fix" img "rotate=-90deg with rgbimage notit"

To display a gray image use with image in place of with rgbimage, e.g.:

img = testimage("walkbridge");
@gp palette(:viridis) "set size square" "set autoscale fix" img "rotate=-0.5pi with image notit"

Note that we used a custom palette (:lapaz, see Palettes and line types) and the rotation angle has been expressed in radians (-0.5pi).

3D plots

3D plots follow the same rules as 2D ones, just replace the @gp macro with @gsp and add the required columns (according to the plotting style).

E.g., to plot a spiral increasing in size along the X direction:

x = 0:0.1:10pi
@gsp cbr=[-1,1].*30  x  sin.(x) .* x  cos.(x) .* x  x./20  "w p pt 7 ps var lc pal"

Note that the fourth array in the dataset, x./20, is used as by gnuplot as point size (ps var). Also note that all the keywords discussed above can also be used in 3D plots.

Palettes and line types

The Gnuplot.jl package comes with all the ColorSchemes palettes readily available.

A gnuplot-compliant palette can be retrieved with palette(), and used as any other command. The previous example may use an alternative palette with:

x = 0:0.1:10pi
@gsp palette(:viridis) cbr=[-1,1].*30 :-
@gsp :-  x  sin.(x) .* x  cos.(x) .* x  x./20  "w p pt 7 ps var lc pal"

The ColorSchemes palettes can also be used to generate line types (actually just line colors), by means of the linetypes() function, e.g.

@gp linetypes(:deepsea)
x = 1:0.1:4pi
for i in 1:5
    @gp :- x i.* sin.(x) "w l notit lw 5"
end

The list of all available palette can be retrieved with palette_names():

julia> palette_names()
450-element Array{Symbol,1}:
 :BuPu_6
 :Spectral_4
 :lighttemperaturemap
 :RdYlGn_5
 :Set2_6
 :PRGn_3
 :greenpink
 :Dark2_7
 :oxy
 :Set2_3
 ⋮
 :Set1_8
 :coolwarm
 :picasso
 :Purples_6
 :BrBG_8
 :flag
 :valentine
 :Oranges_4
 :avocado

Exporting plots to files

Gnuplot.jl to export all plots (as well as multiplots, see Multiplot) to an external file using one of the many available gnuplot terminals. To check which terminals are available in your platform type:

julia> terminals()
59-element Array{String,1}:
 "cairolatex"
 "canvas"
 "cgm"
 "context"
 "domterm"
 "dpu414"
 "dumb"
 "dxf"
 "eepic"
 "emf"
 ⋮
 "tikz"
 "tkcanvas"
 "tpic"
 "unknown"
 "vttek"
 "wxt"
 "x11"
 "xlib"
 "xterm"

(see also terminal() to check your current terminal).

Once you choose the proper terminal (i.e. format of the exported file), use the save() function to export. As an example, all the plots in this page have been saved with:

save(term="pngcairo size 480,360 fontscale 0.8", output="assets/output.png")

Note that you can pass both the terminal name and its options via the term= keyword. See Gnuplot terminals for further info on the terminals.

Gnuplot scripts

Besides exporting plots in a file Gnuplot.jl can also save a script, i.e. a file containing the minimum set of data and commands required to re-create a figure using just gnuplot.

To generate a script for one of the examples above use:

save("script.gp")

after the plot has been displayed. Note that when images or large datasets are involved, save() may store the data in binary files under a directory named <script name>_data. In order to work properly both the script and the associated directory must be available in the same directory.

E.g., the following code:

x = 1:10
@gp x x.^2 "w l"
save("script1.gp")

will produce the following file, named script1.gp:

reset session
$data1 << EOD
 1 1
 2 4
 3 9
 4 16
 5 25
 6 36
 7 49
 8 64
 9 81
 10 100
EOD
plot  \
  $data1 w l
set output

While the following:

img = testimage("lighthouse");
@gp "set size square" "set autoscale fix" img "rotate=-90deg with rgbimage notit"
save("script2.gp")

will produce:

reset session
set size square
set autoscale fix
plot  \
   './script2_data/jl_vH8X4k' binary array=(512, 768) rotate=-90deg with rgbimage notit
set output

The above scripts can be loaded into a pure gnuplot session (Julia is no longer needed) as follows:

gunplot> load 'script1.gp'

to generate a plot identical to the original one.

The purpose of gnuplot scripts is to allow sharing all data, alongside a plot, in order to foster collaboration among scientists and replicability of results. Moreover, a script can be used at any time to change the details of a plot, without the need to re-run the Julia code used to generate it the first time.

Finally, the scripts are the only possible output when Dry sessions are used (i.e. when gnuplot is not available in the user platform.