Optimal synchronization of directed complex networks

TL;DR

This paper develops a theoretical framework for optimizing synchronization in directed networks of coupled oscillators, revealing how network structure and oscillator properties influence synchronization, and identifying key properties of optimal networks.

Contribution

It extends synchronization optimization theory from undirected to directed networks, introducing a generalized synchrony alignment function for systematic network optimization.

Findings

Optimal networks show in-degree heterogeneity matching natural frequency heterogeneity.

Strong correlation between in-degree and natural frequencies enhances synchronization.

Synchronization is promoted by alignment of natural frequencies with dominant Laplacian singular vectors.

Abstract

We study optimal synchronization of networks of coupled phase oscillators. We extend previous theory for optimizing the synchronization properties of undirected networks to the important case of directed networks. We derive a generalized synchrony alignment function that encodes the interplay between network structure and the oscillators' natural frequencies and serves as an objective measure for the network's degree of synchronization. Using the generalized synchrony alignment function, we show that a network's synchronization properties can be systematically optimized. This framework also allows us to study the properties of synchrony-optimized networks, and in particular, investigate the role of directed network properties such as nodal in- and out-degrees. For instance, we find that in optimally rewired networks the heterogeneity of the in-degree distribution roughly matches the heterogeneity of the natural frequency distribution, but no such relationship emerges for out-degrees. We also observe that a network's synchronization properties are promoted by a strong correlation between the nodal in-degrees and the natural frequencies of oscillators, whereas the relationship between the nodal out-degrees and the natural frequencies has comparatively little effect. This result is supported by our theory, which indicates that synchronization is promoted by a strong alignment of the natural frequencies with the left singular vectors corresponding to the largest singular values of the Laplacian matrix.