Physica A 390 (2011) 4621–4626
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Physica A
journal homepage: www.elsevier.com/locate/physa
Changing motif distributions in complex networks by manipulating
rich-club connections
Xiao-Ke Xu
a,b,∗
, Jie Zhang
c
, Ping Li
a
, Michael Small
a
a
Department of Electronic and Information Engineering, Hong Kong Polytechnic University, Hong Kong, People’s Republic of China
b
School of Communication and Electronic Engineering, Qingdao Technological University, Qingdao 266520, People’s Republic of China
c
Centre for Computational Systems Biology, Fudan University, Shanghai 200433, People’s Republic of China
a r t i c l e i n f o
Article history:
Received 11 January 2011
Received in revised form 15 June 2011
Available online 6 July 2011
Keywords:
Complex network
Rich-club connection
Motif
Subgraph
a b s t r a c t
The role of rich-club connectivity is significant in the structural property and functional
behavior of complex networks. In this study, we find whether or not a very small portion
of rich nodes connected to each other can strongly affect the frequency of occurrence
of basic building blocks (motifs) within a heterogeneous network. Conversely whether
a homogeneous network has a rich-club or not generally has no significant effect on
its structure. These findings open the possibility to optimize and control the structure
of complex networks by manipulating rich-club connections. Furthermore, based on the
subgraph ratio profile, we develop a more rigorous approach to judge whether a network
has a rich-club or not. The new method does not calculate how many links there are among
rich nodes but depends on how the links among rich nodes can affect the overall structure
as well as the function of a given network.
© 2011 Elsevier B.V. All rights reserved.
1. Introduction
The motif, defined as a small connected subgraph that recurs in a graph, is the basic building block, or functional
unit, of complex networks [1]. In real-world networks (e.g., gene regulatory networks), motifs represent the elementary
interaction patterns between small groups of nodes, and the relative frequencies with which motifs appear represent
different functions of the network [2–4]. Although it has been found that there is a topological relationship between the
large-scale attributes (scale-free and hierarchical) and local interaction patterns (subgraph based) [5], it remains unclear for
the accurate relationship between small functional units and other structural properties, such as rich-club connections, of
complex networks. In our previous study we found that rich-club connections can dominate some global properties (e.g.,
assortativity and transitivity) of a network [6], which implies the possible relation between the rich-club property and the
network’s subgraph organization.
The rich-club property refers to the organization pattern of rich nodes [7], especially whether rich nodes tend to connect
to one another, or with the remaining nodes [8–13]. Because rich nodes often play a central role in the static properties of,
and dynamic processes on, complex networks [14–16], significant attention has been paid to the prominent effects of the
richest elements [17] and the organization among them [6,18]. A systematic framework is needed to clearly understand the
roles of rich nodes in different real-world networks with distinct degree distributions.
In this study, we find the influences of rich nodes and their organization pattern depends largely on the degree
distributions of complex networks. Rich nodes are important in scale-free networks [19], because a power-law degree
∗
Corresponding author at: Department of Electronic and Information Engineering, Hong Kong Polytechnic University, Hong Kong, People’s Republic
of China.
E-mail address: xiaokeeie@gmail.com (X.-K. Xu).
0378-4371/$ – see front matter © 2011 Elsevier B.V. All rights reserved.
doi:10.1016/j.physa.2011.06.069