We will review some of the major results in random graphs and some of the more challenging open problems. We will cover algorithmic and structural questions. We will touch on newer models, including those related to the WWW.

Random graphs

R J Baxter 1982 London: Academic xii + 486 pp price £43.60 Over the past few years there has been a growing belief that all the twodimensional lattice statistical models will eventually be solved and that it will be Professor Baxter who solves them. Baxter has inherited the mantle of Onsager who started the process by solving exactly the two-dimensional Ising model in 1944.

Exactly Solved Models in Statistical Mechanics

Feel lonely? What about reading books? Book is one of the greatest friends to accompany while in your lonely time. When you have no friends and activities somewhere and sometimes, reading book can be a great choice. This is not only for spending the time, it will increase the knowledge. Of course the b=benefits to take will relate to what kind of book that you are reading. And now, we will concern you to try reading models of man as one of the reading material to finish quickly.

Models of man

Cours d'economie politique

We discuss models and data of crowd disasters, crime, terrorism, war and disease spreading to show that conventional recipes, such as deterrence strategies, are often not effective and sufficient to contain them. Many common approaches do not provide a good picture of the actual system behavior, because they neglect feedback loops, instabilities and cascade effects. The complex and often counter-intuitive behavior of social systems and their macro-level collective dynamics can be better understood by means of complexity science. We highlight that a suitable system design and management can help to stop undesirable cascade effects and to enable favorable kinds of self-organization in the system. In such a way, complexity science can help to save human lives.

/pdf/saving-human-lives-what-complexity-science-and-information-4nyf32oi2l.pdf

Saving human lives: what complexity science and information systems can contribute

In this paper we develop an interbank market with heterogeneous financial institutions that enter into lending agreements on different network structures. Credit relationships (links) evolve endogenously via a fitness mechanism based on agents’ performance. By changing the agent’s trust on its neighbor’s performance, interbank linkages self-organize themselves into very different network architectures, ranging from random to scale-free topologies. We study which network architecture can make the financial system more resilient to random attacks and how systemic risk spreads over the network. To perturb the system, we generate a random attack via a liquidity shock. The hit bank is not automatically eliminated, but its failure is endogenously driven by its incapacity to raise liquidity in the interbank network. Our analysis shows that a random financial network can be more resilient than a scale free one in case of agents’ heterogeneity.

/pdf/systemic-risk-on-different-interbank-network-topologies-26pm15e92q.pdf

Systemic risk on different interbank network topologies

We introduce an order driver market model with heterogeneous traders that imitate each other on a dynamic network structure. The communication structure evolves endogenously via a fitness mechanism based on agents performance. We assess under which assumptions imitation, among noise traders, can give rise to the emergence of gurus and their rise and fall in popularity over time. We study the wealth distribution of gurus, followers and non followers and show that traders have an incentive to imitate and a desire to be imitated since herding turns out to be profitable. The model is then used to study the effect that different competitive strategies (i.e. chartist & fundamentalist) have on agents performance. Our findings show that positive intelligence agents cannot invade a market populated by noise traders when herding is high.

/pdf/herding-effects-in-order-driven-markets-the-rise-and-fall-of-5d91rooehx.pdf

Herding effects in order driven markets: The rise and fall of gurus

We study a credit network and, in particular, an interbank system with an agent-based model. To understand the relationship between business cycles and cascades of bankruptcies, we model a three-sector economy with goods, credit and interbank market. In the interbank market, the participating banks share the risk of bad debits, which may potentially spread a bank’s liquidity problems through the network of banks. Our agent-based model sheds light on the correlation between bankruptcy cascades and the endogenous economic cycle of booms and recessions. It also demonstrates the serious trade-off between, on the one hand, reducing risks of individual banks by sharing them and, on the other hand, creating systemic risks through credit-related interlinkages of banks. As a result of our study, the dynamics underlying the meltdown of financial markets in 2008 becomes much better understandable.

Bankruptcy Cascades in Interbank Markets

/pdf/bankruptcy-cascades-in-interbank-markets-1e5xjgcauv.pdf

Bankruptcy cascades in interbank markets.

In this paper we investigate the sources of instability in credit and financial systems and the effect of credit linkages on the macroeconomic activity. By developing an agent-based model, we analyze the evolving dynamics of the economy as a complex, adaptive and interactive system, which allows us to explain some key events that occurred during the recent economic and financial crisis. In particular, we study the repercussions of inter-bank connectivity on banks’ performances, bankruptcy waves and business cycle fluctuations. Interbank linkages, in fact, not only allow participants to share risk but also create potential for one bank’s crisis to spread through the network. The purpose of the model is, therefore, to build up the dependence among agents at the micro-level and to estimate their impact on the macro stability.

/pdf/markets-connectivity-and-financial-contagion-4bf67m5dxr.pdf

Gabriele Tedeschi

Papers

Systemic risk on different interbank network topologies

Herding effects in order driven markets: The rise and fall of gurus

Bankruptcy Cascades in Interbank Markets

Bankruptcy cascades in interbank markets.

Markets connectivity and financial contagion