## Some TikZ tips

Here I gather some pieces of advice regarding TikZ figures. Some external
references for TikZ are of course the official
manual which has
some great tutorials in it, along an exhaustive documentation of the library.
Its chapter *I.7 Guidelines on Graphics* develops some ideas on general use of
graphic elements in scientific writing, and is quite independant from TikZ
technicalities. I also recommend checking out Overleaf's introduction to
TikZ which contains a
lighter introduction to the principles of the library.

### Colors

I have a dedicated page that list the colors pre-defined when using TikZ as well as some operations allowed under TikZ's color model.

I usually define my own color scheme, and stick to it along the whole document.
The default TikZ colors tend to be quite kitschy.
Below is the palette that I currently use.
It is available as a colors.tex file that I just import into my main document and which redefines some default colors.
Do not hesitate to use opacity variations of those colors (`blue!20`

instead of `blue`

for example).
This is also shown in the different rows in the picture below.
Also do not hesitate to tweak it to your liking, there are a lot of helpful websites out there dedicated to colorscheme design.

### Lines and Arrows

The `thick`

and `ultra thick`

parameters tend to make things more pleasant to look at.
Another classic one: the default arrows are not very good looking to me, so use a replacement for them. A good list of options is available at this page. I usually go with the following:

```
\usetikzlibrary{arrows}
\begin{tikzpicture}[>=stealth']
...
\end{tikzpicture}
```

### Externalization

When the amount and the complexity of the figures increase in the document, it
is helpful to externalize their compilation, so that they are not compiled at
each new iteration of the document. You might need to enable shell escaping for
this to (*e.g.* with `latexmk --shell-escape ...`

).

```
\usetikzlibrary{external}
\tikzexternalize[prefix=compiled_figures/] % prefix sets where to store figures
```

It is sometimes useful to disallow externalization for specific figures.

```
% this disallows the externalization of the very next TikZ figure
\tikzset{external/export next=false}
\begin{tikzpicture}
...
\end{tikzpicture}
```

```
% this disallows externalizations of all figures produced by the todo package
\makeatletter
\renewcommand{\todo}[2][]{\tikzexternaldisable\@todo[#1]{#2}\tikzexternalenable}
\makeatother
```

It can also be useful to set the name of tikz figures, so that your pre-compiled
figures are easily recognizable. Otherwise you would just get a folder full of
`figure-1`

, `figure-2`

and so on.

```
\tikzsetnextfilename{informative_figure_name}
\begin{tikzpicture}
...
\end{tikzpicture}
```

Also note that Overleaf has some special rules for using locally pre-compiled figures (*cf* this documentation). Basically, pre-compiled files should start by `output-`

, so you should set the externalization plugin with something in the spirit of:

```
\usetikzlibrary{external}
\tikzexternalize[prefix=compiled_figures/output-]
```

Beware that using externalization for Beamer document can lead to slow
compilations, since many beamer-specific elements will be externalized and will
need to be re-externalized when their order change (*e.g.* when inserting a new
frame). I still need to figure out a nice workaround for this.

### Programming Aspects — Loops, Variables

#### Loops & Variables

The content of this section has been somewhat scary for me for quit a long time, before I realized that it conveyed additional ways of being lazy.
I want to talk about `for`

loops, as well as the use of variables to define quantities.

Using `foreach`

loops is in reality independant of TikZ (since it relies on
LaTeX features), but works particularly well in conjunction with TikZ. I point
out to the section 88 of the official manual *88. Repeating Things* for a
precise overview of the syntax and the possibilities.

The basic syntax to define variables, and to use a foreach statement to produce the following figure is detailled below.

```
\begin{tikzpicture}
\def \mathvariable {\sigma^2};
\def \colorvariable {blue};
\def \alphatransparency {60};
\def \basewidth {0.1cm};
% iterate on the list {1,2,4,8}
\foreach \x in {1,2,4,8} {
% draw a circle at coordinate (1.5*x, 0) whose radius is x*basewidth
% use the defined color and transparency
\fill[\colorvariable!\alphatransparency] (1.5*\x, 0) circle (\x * \basewidth)
node[below=1cm, black] {$\mathvariable = \x$} ;
}
\end{tikzpicture}
```

Below is an example that purposingly showcases more intricate aspects of
`foreach`

loops and variables and generates the following figure.

## Click to see the code generating the figure.

```
\begin{tikzpicture}
% the following is equivalent to defining \col as a counter (see the next loop)
% but this showcases zipped loops
\foreach \color / \col in {
blue/0, darkblue/1, red/2, orange/3, green/4,
palegreen/5, yellow/6, brokenwhite/7, brokengrey/8} {
\foreach \alpha [count=\row] in {100, 97, ..., 30} {
% the step (-3) of the loop is infered from the two first values
% random formula to define an angle for the current point and radius
% see that we can perform computations on variables
\def \angle {180*\row/16 + 30*\col};
\def \radius {0.6*\col};
% define a coordinate (center\color\alpha) (which are expanded to their actual
% value so that we can draw a node it later, and have line from the border
\coordinate (center\color\alpha) at ({\radius*cos(\angle}, {\radius * sin(\angle)});
% draw a filled circle node named (circle\color\alpha) centered
% at (center\color\alpha)
% we define a new node so that lines will leave from the edge of
% the circle and not from its center
\node[circle, fill=\color!\alpha]
(circle\color\alpha) at (center\color\alpha) {};
% make a straight line of dots (to showcase an if statement)
\ifnum \col = \row
\fill[color=\color, xshift=6cm] (0.5*\col, 0) circle (0.2);
\fi
}
}
% this showcases a trick to iterate on couples (i-1,i) using the remember keyword
\foreach \color[remember=\color as \lastcolor (initially blue)] in
{darkblue, red, orange, green, palegreen,
yellow, brokenwhite, brokengrey} {
\foreach \alpha in {100, 97, ..., 30} {
\draw[ultra thick, color=\lastcolor!\alpha]
(circle\lastcolor\alpha) -- (circle\color\alpha);
}
}
\end{tikzpicture}
```

I recommend using this in conjonction with externalization for rather complex figures.

#### Mathematical Expressions

As you can see in the above section, we were able to define variables through mathematical expressions, for example as

```
\def \angle {180*\row/16 + 30*\col};
\def \radius {0.6*\col};
\coordinate (center) at ({\radius*cos(\angle}, {\radius * sin(\angle)});
```

Those operations are handled by `pgfmath`

under the hood.
Documentation on those operations is available in section 94 of TikZ's manual (*94. Mathematical Operation*, under *Part VIII. Mathematical and Object-Oriented Engines*).
For easy-reference, here are the basic mathematical functions that can be used in such expressions. Individual documentation is available in
*94.3 Syntax for Mathematical Expressions: Functions*.

`abs, acos, add, and, array, asin, atan, atan2, bin, ceil, cos, cosec, cosh, cot, deg, depth, dim, div, divide, e, equal, factorial, false, floor, frac, gcd, greater, height, hex, Hex, int, ifthenelse, iseven, isodd, isprime, less, ln, log10, log2, max, min, mod, Mod, multiply, neg, not, notequal, notgreater, notless, oct, or, pi, pow, rad, rand, random, real, rnd, round, scalar, sec, sign, sin, sinh, sqrt, subtract, tan, tanh, true, veclen, width`

### Plots

To generate nice plots of data, I recommmend using a combination of `matplotlib`

and `seaborn`

, and export them to LaTeX compatible plots using `tikzplotlib`

. So the whole pipeline essentially goes as follows and allows to obtain high quality figures fully rendered with TikZ and pgfplots. One advantage of it is that you can tweak things like axis title, legend, ticks, etc, from inside your LaTeX document, without the need to go inside the code that generated the plot.

```
import matplotlib.pyplot as plt
import seaborn
import tikzplotlib
seaborn.set() # applies the seaborn default settings
# you can costumize those settings, e.g. to use the colorscheme of your document
plt.plot(whatever)
tikzplotlib.save("figure.tex", wrap=False) # wrap controls the standaloneness of the tex figure
```

### Graphs

To work with graphs, I recommend using `networkX`

to manipulate them and
`network2tikz`

to export them to TikZ with a nice control over the layout, the
format, and so on. Moreover, `networkX`

provides many standard algorithms and
graph-processing pipelines, making it easy to create complex illustrations.

### Scaling

You can handle the size of TikZ figures using the `scale`

options.

`\begin{tikzpicture}[scale=0.6] % you can also directly set xscale and / or yscale`

The aforementionned `scale`

may break a figure with text, or some fixed-size nodes (this is the case when exporting graph with `network2tikz`

for instance). The following might fix the issue by scaling each and every node. Finding the right amount of *scaling* for both parameters might require a little bit of tweaking though.

`\begin{tikzpicture}[scale=0.6, every node/.style={scale=0.6}]`

## Beamer Tips

### Aspect Ratio

On most modern supports, the default beamer image ratio is not optimal and wastes some space. It is easy to switch to another screen ratio, for instance 16:9 using

`\documentclass[aspectratio=169]{beamer}`

### Slides Template

Teaser. True content coming soon.

## A TikZ gallery

This is still a work in progress, there are a lot more figures to come. I will
also make the source code for each figure accessible by clicking on them. The
source code will be provided as a standalone tex file. It should compile as
provided, using the `latexmk -pdf source.tex`

command. The only requirements
is that it uses the `colors.tex`

file mentionned earlier,
so make sure to have it accessible from your latex source.

### Basic Elements

Coming soon (collection of basic atomic elements to serve as a quick access list).

### More Advanced Figures

### Figures Made By My Esteemed Colleagues

Here is a collection of figures that colleagues have kindly offered to share here.

#### Yoann Coudert — Osmont

Here are some images by Yoann Coudert — Osmont.

#### Amadeus Reinald

Here are some images by Amadeus Reinald.