I'm wondering if there is a clear method that can be used to create the bipartite network to connect the samples with OTUs/taxa. As I searched the internet, all of the tutorials are talking about how to plot it but not how to calculate or how to get the associations between samples and taxa. Also, the papers that used bipartite network are unclear about the methods either. Although the qiime have the function to get the nodes and edges for bipartite (http://qiime.org/scripts/make_bipartite_network.html), it is unclear how qiime does the analysis. So what is the method/algorithm behind this?