I attended a really nice talk by Arash Amini yesterday about detecting ‘communities’ in sparse graphs. The basic problem is: In a big graph (like the Facebook graph, or the graph of scientific papers citations) you have clusters of friends/associates, and you want to pick out those clusters. Dr. Amini and his collaborators have been working on methods to solve this problem in particularly noisy cases. The methods presented were developed for cases where you know the specific number of clusters you are seeking to find. It was a fascinating talk, and I came away wondering if there are good methods to use when you aren’t sure of how many clusters there are.