Degree distributions under general node removal: Power-law or Poisson?

TL;DR

This paper investigates how different node removal strategies affect the degree distribution of networks, revealing conditions under which the distribution resembles either a power-law or a Poisson form, using entropy-based classification.

Contribution

It introduces a unified framework using relative entropy to classify degree distribution changes under various node removal scenarios, including hub protection.

Findings

Two distinct regimes identified: power-law-like and Poisson-like degree distributions.

The classification depends on the node removal strategy and the level of hub protection.

The approach combines simulations and rate equation analysis for comprehensive insights.

Abstract

Perturbations made to networked systems may result in partial structural loss, such as a blackout in a power-grid system. Investigating the resultant disturbance in network properties is quintessential to understand real networks in action. The removal of nodes is a representative disturbance, but previous studies are seemingly contrasting about its effect on arguably the most fundamental network statistic, the degree distribution. The key question is about the functional form of the degree distributions that can be altered during node removal or sampling, which is decisive in the remaining subnetwork's static and dynamical properties. In this work, we clarify the situation by utilizing the relative entropies with respect to the reference distributions in the Poisson and power-law form. Introducing general sequential node removal processes with continuously different levels of hub protection to encompass a series of scenarios including random removal and preferred or protective removal of the hub, we classify the altered degree distributions starting from various power-law forms by comparing two relative entropy values. From the extensive investigation in various scenarios based on direct node-removal simulations and by solving the rate equation of degree distributions, we discover in the parameter space two distinct regimes, one where the degree distribution is closer to the power-law reference distribution and the other closer to the Poisson distribution.