Catálogo de publicaciones - libros

We develop complex networks that represent activities in the economy. The network in this study is constructed from firms and the relationships between firms, i.e., shareholding, interlocking directors, transactions, and joint applications for patents. Thus, the network is regarded as a multigraph, and it is also regarded as a weighted network. By calculating various network indices, we clarify the characteristics of the network. We also consider the dynamics of firms in the production space that are characterized by capital stock, employment, and profit. Each firm moves within this space to maximize their profit by using controlling of capital stock and employment. We show that the dynamics of rational firms can be described using a ridge equation. We analytically solve this equation by assuming the extensive Cobb-Douglas production function, and thereby obtain a solution. By comparing the distribution of firms and this solution, we find that almost all of the 1,100 firms listed on the first section of the Tokyo stock exchange and belonging to the manufacturing sector are managed efficiently.

A first analysis of the Italian system of banks and firms was carried out using an approach based on network theory. The emerging architecture of this economic network shows peculiar behaviors. Big banks are creditors of many firms; among these, big firms are financed by several banks. On the contrary, small firms are preferentially financed by small banks, covering very often the entire credit they need.

Scientific collaboration network gives a nice description for communications among scientists. In order to show the status of the research in Econophysics, we have collected papers in Econophysics and constructed a network of scientific communication to integrate idea transportation among econophysicists by collaboration, citation and personal discussion. Inspired by scientific collaboration networks, especially our empirical analysis of econophysicists network, an evolutionary model for weighted networks is proposed. The model shows the scale-free phenomena in degree and vertex weight distribution. The results of short term evolution are consistent well qualitatively with the empirical results.

Revision and extension of a paper, ‘U.S. wage income since 1961: the perceived inequality trend’, presented to the annual meetings of the Population Association of America, March–April 2005, Philadelphia, Pennsylvania, USA. On-line at: http://paa2005.princeton.edu/download.aspx?submission ID=50379 .

Almost all societies, once they attain a certain level of complexity, exhibit inequality in the income of its members. Hierarchical stratification of social classes may be a major contributor to such unequal distribution of income, with intra-class variation often being negligible compared to inter-class differences. In this paper, examples from different historical periods, such as 10th century Byzantium and the Mughal empire of India in the 15th century, and different kinds of organizations, such as a criminal gang in the USA and Manufacturing & IT Services companies in India, are shown to suggest a causal relation between the hierarchical structure of social organization and the observed income inequality in societies. Proceeding from the assumption that income inequality may be a consequence of resource flow in a hierarchically structured social network, we present a model to show that empirically observed long-tailed income distribution can be explained through a process of division of assets at various levels in a hierarchical organization.

We consider an R&D race between two symmetric firms. The game consists of two stages. In the first stage, firms non-cooperatively decide upon their levels of investment in R&D which, in turn, determine the Poisson probabilities of their subsequent sucesses. In the second stage, they engage in a Nash bargaining game to share their knowledge. We show that the firms over-invest and earn lower profits if knowledge sharing is possible compared to the situation where it is not. Hence, before the first stage, if the firms are given the option of precommitting to no knowledge sharing, they will do so and be better off. The society, of course, would be better off with full knowledge sharing.

We show the existence of a first best incentive compatible mechanism for the queueing model that satisfies identical preferences lower bound. We call this mechanism the FB′ mechanism. We also show that for the queueing model, either with three agents or with four agents, the FB′ mechanism is the only first best incentive compatible mechanism that satisfies identical preferences lower bound.

Generalisation of the El Farol bar problem to that of many bars here leads to the Kolkata restaurant problem, where the decision to go to any restaurant or not is much simpler (depending on the previous experience of course, as in the El Farol bar problem). This generalised problem can be exactly analysed in some limiting cases discussed here. The fluctuation in the restaurant service can be shown to have precisely an inverse cubic behavior, as widely seen in the stock market fluctuations.

So far econophysics has given contributions in four areas of economics: financial markets, wealth and income distribution, industrial economics ( firms’ size distribution, growth rates ) and, more recently, networks analysis. According to Gallegati et al., 2006, there are some weakness in the approach: a lack of awareness of work that has been done within economics itself; resistance to more rigorous and robust statistical methodology; the belief that universal empirical regularities can be found in many areas of economic activity; the theoretical models which are being used to explain empirical phenomena. The paper raised a lively debate (see e.g. Ball, 2006).