Dual SOM

Posted: February 19, 2009 at 8:04 pm

I’ve started exploring the idea of having two SOMs. The first SOM simply chooses which images should be stored, using a cyclic learning function. The second SOM uses a linear SOM and is trained on the (finite) results of the first SOM in order to make a highly organized map. The second SOM is fed with input data in random order, not the original order received by the camera. The first experiment used two SOMs of the same size (30×30 units). The problem was that the massive number of iterations possible in the first SOM just don’t scale to the second SOM (of the same size, but needing to optimize between dreams). The result is that the first SOM may have all its memory locations occupied, but the second SOM is unable to occupy all its locations. This is the case even when using the codebooks for the first SOM in the second.

Here is a U-Matrix of the hists of images stored in the first SOM:


The second SOM:


Here is an example of the second SOM with fewer units (15×15):


This shows the memory field for the above SOM:


I’m currently training a 75×75 unit SOM and will use that to feed smaller second stage SOMs.