The End
This concludes the tutorial on plots in Julia.
The next section explains how to save plots, for example to include them in your reports. Feel free to skip that section if you are not interested, you won't need it in this class!
In any case, the third and last notebook for this week awaits you on Moodle.
Plot attributes
Some attributes can be used to modify the entire plot.
A plot can contain multiple subplots, but we won't cover that in this tutorial. However this means that the official documentation has a page for plot attributes and a page for subplot attributes .
Here is a selection:
title: Change the title displayed at the top of the plot.
legend: Position of the legend. false can be used to disable the legend.
dpi: "Dots Per Inch" of the output figure. Can be used to increase the quality of figures saved as an image. (See below). Default is 100.
Plot attributes are also passed to plot / plot!. They can be passed at the same time as a series, or separately such as
plot!(; title="My title")As usual, here is an example:
To plot a continuous function, we use the following principle:
Generate many x coordinates with range(a, b, length=N).
Compute the corresponding y coordinates by calling the function.
Here is a plot of the sin function between $0$ and $\pi$ :
°persist_js_state¤mimeimage/svg+xml²last_run_timestampËAÚw™üB¥Q·has_pluto_hook_features¬rootassigneeÀ§cell_idÙ$5c79aebd-5be4-4c48-830a-a639fd8af90b¹depends_on_disabled_cells§runtimeÎ °ƒ»µpublished_object_keys¸depends_on_skipped_cells§erroredÂÙ$42e8bbcd-cfe8-4310-957c-6114af395401Š¦queued¤logs§running¦output†¤bodyÚ]Axis attributes
Some attributes can also apply to the x axis (horizontal) or the y axis (vertical). Here is a selection:
xscale and yscale: Scale of the axis. Most importantly, :log10 can be passed to make the axis logarithmic.
xlabel and ylabel: Name of the axis.
xlims and ylims: Range of the axis. For example, [5, 10] to make the axis range from 5 to 10.
The full list is available in the official documentation , without the x or y prefix.
Here is an example:
°persist_js_state¤mimeimage/svg+xml²last_run_timestampËAÚw™üãfÓ·has_pluto_hook_features¬rootassigneeÀ§cell_idÙ$8aee946d-6134-413d-9ff5-cb56f26c5e0c¹depends_on_disabled_cells§runtimeÎàY
µpublished_object_keys¸depends_on_skipped_cells§erroredÂÙ$76dd1c63-b5fd-465b-a8df-9f87cbacf43cŠ¦queued¤logs§running¦output†¤bodyÚ¬
In Julia, functions that perform a modification often end with a ! by convention. Plots follows this convention:
Similarly, scatter(...) creates a new plot while scatter!(...) modifies an existing plot.
Here is an example of plotting a new line with plot then adding some points with scatter!:
°persist_js_state¤mime©text/html²last_run_timestampËAÚw™Ï†µÌ·has_pluto_hook_features¬rootassigneeÀ§cell_idÙ$76dd1c63-b5fd-465b-a8df-9f87cbacf43c¹depends_on_disabled_cells§runtimeÎ Ùµpublished_object_keys¸depends_on_skipped_cells§erroredÂÙ$26e79728-14f5-4cda-bcd1-7839afae8f5cŠ¦queued¤logs§running¦output†¤body °persist_js_state¤mimeªtext/plain²last_run_timestampËAÚw™ýBtd·has_pluto_hook_features¬rootassigneeÀ§cell_idÙ$26e79728-14f5-4cda-bcd1-7839afae8f5c¹depends_on_disabled_cells§runtimeÎ `S$µpublished_object_keys¸depends_on_skipped_cells§erroredÂÙ$b21e501d-afb3-4612-b46e-b68d360c387aŠ¦queued¤logs§running¦output†¤bodyÈO¼
°persist_js_state¤mimeimage/svg+xml²last_run_timestampËAÚw™ü$* ·has_pluto_hook_features¬rootassigneeÀ§cell_idÙ$b21e501d-afb3-4612-b46e-b68d360c387a¹depends_on_disabled_cells§runtimeÎ þíµpublished_object_keys¸depends_on_skipped_cells§erroredÂÙ$1a24369e-b83d-4ff7-a75f-ff80ffb2e932Š¦queued¤logs§running¦output†¤bodyÈ\•
°persist_js_state¤mimeimage/svg+xml²last_run_timestampËAÚw™üJ³·has_pluto_hook_features¬rootassigneeÀ§cell_idÙ$1a24369e-b83d-4ff7-a75f-ff80ffb2e932¹depends_on_disabled_cells§runtimeÎ ù µpublished_object_keys¸depends_on_skipped_cells§erroredÂÙ$f70510e2-4f93-44a6-a883-0ca438f86fe0Š¦queued¤logs§running¦output†¤bodyÙ_PDF
An example of saving a figure to PDF:
°persist_js_state¤mimeimage/svg+xml²last_run_timestampËAÚw™ý"vG·has_pluto_hook_features¬rootassigneeÀ§cell_idÙ$f92a25a4-6cc5-4705-956a-8da3af041636¹depends_on_disabled_cells§runtimeÎ æµpublished_object_keys¸depends_on_skipped_cells§erroredÂÙ$dc34fd9a-aa31-4196-9c9b-7e0d1dd90b33Š¦queued¤logs§running¦output†¤body °persist_js_state¤mimeªtext/plain²last_run_timestampËAÚw™ý,¬ë·has_pluto_hook_features¬rootassigneeÀ§cell_idÙ$dc34fd9a-aa31-4196-9c9b-7e0d1dd90b33¹depends_on_disabled_cells§runtimeÎÌEݵpublished_object_keys¸depends_on_skipped_cells§erroredÂÙ$4afdacc0-65b9-4f23-8b0e-bd2af8bffb91Š¦queued¤logs§running¦output†¤bodyÚsLaTeX Strings
LaTeX-formatted strings can be used in the plots:
If the entire string needs to be understood as a LaTeX formula, simply add L in front: L"\frac{1}{2}".
Otherwise, add an L in front and put the LaTeX formula inside $ characters in the string: L"one half: $\frac{1}{2}$".
(Note that this requires the LaTeXStrings package to be used).
Here is a small example:
Image
An example of saving a figure to PNG:
If you open the above image, you will notice that it looks blurry. For example it might look like this:
The number of pixels used by the image can be increased with the dpi attribute:
Series attributes
Each dataset added through plot or scatter is called a series . Additional options can be passed, called attributes . A full list is available in the official documentation . Here is a selection:
label: Changes the name of the series in the legend.
color or c: Changes the color of the series.
linestyle or ls: Changes the style of the line. For example :solid or :dot.
linewidth or lw: Width of the line in pixels. We will often use lw=2 since the default 1 is quite thin.
markerstyle or mark: Changes the style of markers, for example :o for round markers. We will often use mark=:o to see the individual data points in a line plot.
These also apply to scatter (and other types of plots).
Here is a showcase of all of these options:
°persist_js_state¤mimeimage/svg+xml²last_run_timestampËAÚw™ü+üY·has_pluto_hook_features¬rootassigneeÀ§cell_idÙ$022f2355-639d-42e4-91eb-27c8af7e3afa¹depends_on_disabled_cells§runtimeÎ ”µpublished_object_keys¸depends_on_skipped_cells§erroredÂÙ$1c0985d7-d63e-40de-9732-9fd31d3e97a0Š¦queued¤logs§running¦output†¤body °persist_js_state¤mimeªtext/plain²last_run_timestampËAÚw™ý5sÒ·has_pluto_hook_features¬rootassigneeÀ§cell_idÙ$1c0985d7-d63e-40de-9732-9fd31d3e97a0¹depends_on_disabled_cells§runtimeÎGfŠµpublished_object_keys¸depends_on_skipped_cells§erroredÂÙ$38004ae9-7f5b-4c4d-8d1a-0962c3def007Š¦queued¤logs§running¦output†¤bodyÚ)Optional: Saving plots
(This is not needed for this course, but could be useful to you in the future.)
The plot / plot! function returns the current plot, which Pluto renders. This is how we have been rendering plots so far. To save a plot, for example to include it in a report, we use the savefig function.
We have to pass the name of the file to savefig.
Pass a file name ending with .pdf to save the plot as a PDF document. This will save the plot as vector graphics , which means that the plot will not be blurry even when zooming in a lot.
Pass a file name ending with an image extension such as .png to save the plot as an image. Images can be easier to work with, but can look blurry when zoomed in.
In reports, prefer vector graphics... they look better. 😉
Scatter plots
Scatter plots are also common. Each point is represented by a dot, and the points don't get connected together. For example:
