SelfOrganizingMap v0.1

http://en.wikipedia.org/wiki/Self-organizing_map

FROM WIKIPEDIA: A self-organizing map (SOM) or self-organizing feature map (SOFM) is a type of artificial neural network that is trained using unsupervised learning to produce a low-dimensional (typically two-dimensional), discretized representation of the input space of the training samples, called a map. Self-organizing maps are different from other artificial neural networks in the sense that they use a neighborhood function to preserve the topological properties of the input space.

This makes SOM useful for visualizing low-dimensional views of high-dimensional data, akin to multidimensional scaling. The model was first described as an artificial neural network by the Finnish professor Teuvo Kohonen, and is sometimes called a Kohonen map.

Realistically, SOMs are a form of k-means clustering, where the prototypes are constrained to live and play in a two dimensional grid, or map. They have one big advantage - they achieve a very nice dimensionality reduction, especially suited for visualizing the relationships between the points. Because they do this nonlinearly, they have in some circumstances an edge over linear projection methods.

This library implements the online version of the self-organizing map. It's only dependency is the SciPy / NumPy pack.

v0.4

• improve NN search algorithms for BMUs
• fine-tune the alpha and neighborhood functions in the prototype shift step.
• make online learning algorithm a bit more flexible

v0.3

• get json output working for use with protovis or processing
• get processing prototypes finished - DONE

v0.2

• generalize to any distance function - DONE
• implement the hexagonal grid - DONE
• finish the batch learning version
• reimplement the alpha function to work better in online learning.

v0.1 (current)

• implement the online algorithm - DONE
• verify with some tests that algorithm fits the map - DONE

todo:

• implement batch learning
• implement better online learning
• create appropriate map visualizations
• output results in json format for use with something like protovis (perhaps a separate project altogether)