## Dynamic systems, bifurcations, procedural worlds

I’m using pgfplots a lot, so I will share some examples today.

Here, I benefit from these features of pgfplots, going beyond base TikZ:

• Simple plotting with 3d coordinates and axonometric projection
• Presentation of required coordinate axes
• Reading in files with externally calculated data

In any case we can use Lua for calculating data. Lua generates the TeX commands for printing, which will be processed in a pgfplots axis environment.

Here are the samples, just click on it to get to the corresponding thread on TeXwelt with full source code.

## Lorenz attractor (dynamic system)

While I posted a Python calculated version on TeXwelt.de, Henri added one, which bases on LuaTeX. Let’s see his picture at first:

Of pgfplots I used the transparency feature besides the standard 3d plot, so I got an impression of the density:

Once we calculated the data, the code is simple:

 \documentclass[border=10pt]{standalone} \usepackage{pgfplots} \begin{document} \begin{tikzpicture} \begin{axis}[ xmin = -25, xmax = 25, ymin = -25, ymax = 25, zmin = 0, zmax = 50, hide axis, ] \addplot3[mark=none, mesh, shader=interp, color=black, opacity=0.2] file { lorenz.dat }; \end{axis} \end{tikzpicture} \end{document}

## Fractal landscapes – the base for producing procedural worlds

Between adjacent points, new points will be calculated, with random but limited variation. Finally we will get a mountainous landscaoe. The calculated points get color according to their height: blue for sea level and below, green for mountains and white above the snowline.

Next step: specify nice starting values, for beginning with a certain base structure, such as an island in the water.

## Feigenbaum diagram (bifurkations)

This is a classic of the chaos theory und closely related to the Mandelbrot set. Also here, we use transparency for an impression of the point density.

I often started such topics on TeXwelt.de. LaTeX support for thesis writers is not the only talking point there. It became established, that TeX connoisseurs post their ideas in shape of a question, often themselves posting the first answer, opening a discussion. The final goal is a knowledge database, built on top of questions and answers.

08. July 2014 by stefan