I have written a simple SOM algorithm in MATLAB. My big challenge is that, how can I visualize/plot data in the format of U-Matrix, Sample Hits and Component/Input Planes? These three plots exists in the SOM toolbox in MATLAB. But the problem is that I cannot call them to visualize my data over my written code. Because they need a 'net' as input in which my code does not make any 'net'.
Is there any guidance?
You can create your own functions as they are not too complicated. I will assume a SOM of 20x20x10 (400 nodes, 4 features) for explanation.
The Hit-Map is no more than giving each sample to the already learned SOM and incrementing +1 to the node that was chosen as the Best Matching Unit (BMU). Then you plot this map. So if node(1,1) fires 10 times, and node(1,2) fires 100 times, then you will have an image where node(1,2) has a higher intensity than node(1,1).
The U-Matrix is a map representing the average distance between the node's weight vector and its closest neighbours. So here you can calculate the Euclidean distance between the feature vector of node X to every neighbour. So if you had a feature vector for node(1,1,:)=[1,1,2,3], node(1,2,:)=[2,2,1,1], and node(2,1,:)=[1,1,1,1], then the value of the U-matrix for node(1,1) could be U(1,1)=norm(squeeze(node(1,1,:)-node(1,2,:)))+norm(squeeze(node(1,1,:)-node(2,1,:)))=4.8818
The Component/Input Planes is the simplest one and does not require any processing. You just basically pick each feature of the SOM map and plot. So in our example of a 20x20x4 SOM, you would have 4 features and therefore 4 components, which you can plot through imagesc(node(:,:,1)) for feature 1
