Clustering of the structures by using "snakes-and-dragons" approach, or correlation matrix as a signal

Biological, ecological, social, and technological systems are complex structures with multiple interacting parts, often represented by networks. Correlation matrices describing interdependency of the variables in such structures provide key information for comparison and classification of such systems. Classification based on correlation matrices could supplement or improve classification based on variable values, since the former reveals similarities in system structures, while the latter relies on the similarities in system states. Importantly, this approach of clustering correlation matrices is different from clustering elements of the correlation matrices, because our goal is to compare and cluster multiple networks, not the nodes within the networks. A novel approach for clustering correlation matrices, named snakes-and-dragons, is introduced and illustrated by examples from neuroscience, human microbiome, and macroeconomics.