Self-Organizing Map - Simple demonstration

While there are many sources that provide the pseudo-code of a self-organizing map (SOM), I could not find a simple implementation that clarifies every step of this algorithm which was introduced by Kohonen.

For this reason I implemented this clearly defined Matlab implementation and wanted to share it with you.

As a demonstration I use the RGB 3D training vectors. The trained SOM neurons result in a 2D spatial arrangement such that the neurons that have similar 3D weight vectors (i.e. similar colour representation) are located close to each other.