Input graph: the hidden geometry in controlling complex networks

TL;DR

This paper introduces the input graph, a geometric framework that reveals the relationships among control schemes and input nodes in complex networks, providing insights into network controllability and a method for control scheme design.

Contribution

It proposes the input graph as a novel geometric tool to analyze control schemes, establishing relationships between nodes and control, and explaining bifurcation phenomena in dense networks.

Findings

Input graph reveals relationships among control schemes.

Giant components in input graphs explain bifurcation phenomena.

Method for designing control schemes based on input graph topology.

Abstract

The ability to control a complex network towards a desired behavior relies on our understanding of the complex nature of these social and technological networks. The existence of numerous control schemes in a network promotes us to wonder: what is the underlying relationship of all possible input nodes? Here we introduce input graph, a simple geometry that reveals the complex relationship between all control schemes and input nodes. We prove that the node adjacent to an input node in the input graph will appear in another control scheme, and the connected nodes in input graph have the same type in control, which they are either all possible input nodes or not. Furthermore, we find that the giant components emerge in the input graphs of many real networks, which provides a clear topological explanation of bifurcation phenomenon emerging in dense networks and promotes us to design an efficient method to alter the node type in control. The findings provide an insight into control principles of complex networks and offer a general mechanism to design a suitable control scheme for different purposes.