Université de Fribourg

Study of market model describing the contrary behaviors of informed and uninformed agents: Being minority and being majority

Zhang, Yu-Xia ; Liao, Hao ; Medo, Matúš ; Shang, Ming-Sheng ; Yeung, Chi Ho

In: Physica A: Statistical Mechanics and its Applications, 2016, vol. 450, p. 486–496

In this paper we analyze the contrary behaviors of the informed investors and uniformed investors, and then construct a competition model with two groups of agents, namely agents who intend to stay in minority and those who intend to stay in majority. We find two kinds of competitions, inter- and intra-groups. The model shows periodic fluctuation feature. The average distribution of...

Université de Fribourg

Modeling mutual feedback between users and recommender systems

Zeng, An ; Yeung, Chi Ho ; Medo, Matúš ; Zhang, Yi-Cheng

In: Journal of Statistical Mechanics: Theory and Experiment, 2015, vol. 2015, no. 7, p. P07020

Recommender systems daily influence our decisions on the Internet. While considerable attention has been given to issues such as recommendation accuracy and user privacy, the long-term mutual feedback between a recommender system and the decisions of its users has been neglected so far. We propose here a model of network evolution which allows us to study the complex dynamics induced by this...

Université de Fribourg

Recommender systems

Lü, Linyuan ; Medo, Matúš ; Yeung, Chi Ho ; Zhang, Yi-Cheng ; Zhang, Zi-Ke ; Zhou, Tao

In: Physics Reports, 2012, vol. 519, no. 1, p. 1–49

The ongoing rapid expansion of the Internet greatly increases the necessity of effective recommender systems for filtering the abundant information. Extensive research for recommender systems is conducted by a broad range of communities including social and computer scientists, physicists, and interdisciplinary researchers. Despite substantial theoretical and practical achievements, unification...

Université de Fribourg

The reinforcing influence of recommendations on global diversification

Zeng, An ; Yeung, Chi Ho ; Shang, Ming-Sheng ; Zhang, Yi-Cheng

In: Europhysics Letters - EPL, 2012, vol. 97, no. 1, p. 18005

Recommender systems are promising ways to filter the abundant information in modern society. Their algorithms help individuals to explore decent items, but it is unclear how they distribute popularity among items. In this paper, we simulate successive recommendations and measure their influence on the dispersion of item popularity by Gini coefficient. Our result indicates that local diffusion and...

Université de Fribourg

Tracing the evolution of physics on the backbone of citation networks

Gualdi, Stanislao ; Yeung, Chi Ho ; Zhang, Yi-Cheng

In: Physicval Review E - Statistical, Nonlinear, and Soft Matter Physics, 2011, vol. 84, no. 4, p. 046104

Many innovations are inspired by past ideas in a nontrivial way. Tracing these origins and identifying scientific branches is crucial for research inspirations. In this paper, we use citation relations to identify the descendant chart, i.e., the family tree of research papers. Unlike other spanning trees that focus on cost or distance minimization, we make use of the nature of citations and...

Université de Fribourg

Leaders in social networks, the delicious case

Lü, Linyuan ; Zhang, Yi-Cheng ; Yeung, Chi Ho ; Zhou, Tao

In: PLoS ONE, 2011, vol. 6, no. 6, p. e21202

Finding pertinent information is not limited to search engines. Online communities can amplify the influence of a small number of power users for the benefit of all other users. Users' information foraging in depth and breadth can be greatly enhanced by choosing suitable leaders. For instance in delicious.com, users subscribe to leaders' collection which lead to a deeper and wider reach not...

Université de Fribourg

Enhancing synchronization by directionality in complex networks

Zeng, An ; Son, Seung-Woo ; Yeung, Chi Ho ; Fan, Ying ; Di, Zengru

In: Physical Review E - Statistical, Nonlinear, and Soft Matter Physics, 2011, vol. 83, no. 4, p. 045101

We propose a method called the residual edge-betweenness gradient (REBG) to enhance the synchronizability of networks by assigning the link direction while keeping the topology and link weights unchanged. Direction assignment has been shown to improve the synchronizability of undirected networks in general, but we find that in some cases incommunicable components emerge and networks fail to...

Université de Fribourg

Self-organization in social tagging systems

Liu, Chuang ; Yeung, Chi Ho ; Zhang, Zi-Ke

In: Physical Review E - Statistical Nonlinear, and Soft Matter Physics, 2011, vol. 83, no. 6, p. 06604

Individuals often imitate each other to fall into the typical group, leading to a self-organized state of typical behaviors in a community. In this paper, we model self-organization in social tagging systems and illustrate the underlying interaction and dynamics. Specifically, we introduce a model in which individuals adjust their own tagging tendency to imitate the average tagging tendency. We...

Université de Fribourg

Heterogenous scaling in the inter-event time of on-line bookmarking

Wang, Peng ; Xie, Xiao-Yi ; Yeung, Chi Ho ; Wang, Bing-Hong

In: Physica A: Statistical Mechanics and its Applications, 2011, vol. 390, no. 12, p. 2395-2400

In this paper, we study the statistical properties of bookmarking behaviors in Delicious.com. We find that the inter-event time (τ) distributions of bookmarking decay in a power-like manner as τ increases at both individual and population levels. Remarkably, we observe a significant change in the exponent when the inter-event time increases from the intra-day range to the inter-day range. In...

Université de Fribourg

How to quantify the influence of correlations on investment diversification

Medo, Matúš ; Yeung, Chi Ho ; Zhang, Yi-Cheng

In: International Review of Financial Analysis, 2009, vol. 18, no. 1-2, p. 34-39

When assets are correlated, benefits of investment diversification are reduced. To measure the influence of correlations on investment performance, a new quantity—the effective portfolio size—is proposed and investigated in both artificial and real situations. We show that in most cases, the effective portfolio size is much smaller than the actual number of assets in the portfolio and that it...