Imperial College London

Dr. Eduardo Viegas

Faculty of Natural SciencesDepartment of Mathematics








Electrical EngineeringSouth Kensington Campus





Publication Type

7 results found

Goto H, Viegas E, Takayasu H, Takayasu M, Jensen HJet al., 2019, Dynamics of essential interaction between firms on financial reports, PLoS One, Vol: 14, Pages: 1-16, ISSN: 1932-6203

Companies tend to publish financial reports in order to articulate strategies, disclose key performance measurements as well as summarise the complex relationships with external stakeholders as a result of their business activities. Therefore, any major changes to business models or key relationships will be naturally reflected within these documents, albeit in an unstructured manner. In this research, we automatically scan through a large and rich database, containing over 400,000 reports of companies in Japan, in order to generate structured sets of data that capture the essential features, interactions and resulting relationships among these firms. In doing so, we generate a citation type network where we empirically observe that node creation, annihilation and link rewiring to be the dominant processes driving its structure and formation. These processes prompt the network to rapidly evolve, with over a quarter of the interactions between firms being altered within every single calendar year. In order to confirm our empirical observations and to highlight and replicate the essential dynamics of each of the three processes separately, we borrow inspiration from ecosystems and evolutionary theory. Specifically, we construct a network evolutionary model where we adapt and incorporate the concept of fitness within our numerical analysis to be a proxy real measure of a company’s importance. By making use of parameters estimated from the real data, we find that our model reliably replicates degree distributions and motif formations of the citation network, and therefore reproducing both macro as well as micro, local level, structural features. This is done with the exception of the real frequency of bidirectional links, which are primarily formed as a result of an entirely separate and distinct process, namely the equity investments from one company into another.

Journal article

Viegas EM, Goto H, Takayasu H, Takayasu M, Jensen HJet al., 2019, Assembling real networks from synthetic and unstructured subsets: the corporate reporting case, Scientific Reports, Vol: 9, ISSN: 2045-2322

The analysis of interfirm business transaction networks provides invaluable insight into the trading dynamics and economicstructure of countries. However, there is a general scarcity of data available recording real, accurate and extensive informationfor these types of networks. As a result, and in common with other types of network studies - such as protein interactions forinstance - research tends to rely on partial and incomplete datasets, i.e. subsets, with less certain conclusions. Hereh, wemake use of unstructured financial and corporate reporting data in Japan as the base source to construct a financial reportingnetwork, which is then compared and contrasted to the wider real business transaction network. The comparative analysisbetween these two rich datasets - the proxy, partially derived network and the real, complete network at macro as well as localstructural levels - provides an enhanced understanding of the non trivial relationships between partial sampled subsets andfully formed networks. Furthermore, we present an elemental agent based pruning algorithm that reconciles and preserves keystructural differences between these two networks, which may serve as an embryonic generic framework of potentially wideruse to network research, enabling enhanced extrapolation of conclusions from partial data or subsets.

Journal article

Goto H, Viegas E, Jensen HJ, Takayasu H, Takayasu Met al., 2018, Smoluchowski equation for networks: merger induced intermittent giant node formation and degree gap, Journal of Statistical Physics, Vol: 172, Pages: 1086-1100, ISSN: 1572-9613

The dynamical phase diagram of a network undergoing annihilation, creation, and coagulation of nodes is found to exhibit two regimes controlled by the combined effect of preferential attachment for initiator and target nodes during coagulation and for link assignment to new nodes. The first regime exhibits smooth dynamics and power law degree distributions. In the second regime, giant degree nodes and gaps in the degree distribution are formed intermittently. Data for the Japanese firm network in 1994 and 2014 suggests that this network is moving towards the intermittent switching region.

Journal article

Goto H, Viegas E, Jensen HJ, Takayasu H, Takayasu Met al., 2017, Appearance of unstable monopoly state caused by selective and concentrative mergers in business networks, Scientific Reports, Vol: 7, ISSN: 2045-2322

Recently, growth mechanism of firms in complex business networks became new targets of scientific study owing to increasing availability of high quality business firms’ data. Here, we paid attention to comprehensive data of M&A events for 40 years and derived empirical laws by applying methods and concepts of aggregation dynamics of aerosol physics. It is found that the probability of merger between bigger firms is bigger than that between smaller ones, and such tendency is enhancing year by year. We introduced a numerical model simulating the whole ecosystem of firms and showed that the system is already in an unstable monopoly state in which growth of middle sized firms are suppressed.

Journal article

Broga KM, Viegas E, Jensen HJ, 2016, Model analysis of the link between interest rates and crashes, Physica A - Statistical Mechanics and Its Applications, Vol: 457, Pages: 225-238, ISSN: 0378-4371

We analyse the effect of distinct levels of interest rates on the stability of the financial network under ourmodelling framework. We demonstrate that banking failures are likely to emerge early on under sustainedhigh interest rates, and at much later stage - with higher probability - under a sustained low interest ratescenario. Moreover, we demonstrate that those bank failures are of a different nature: high interest ratestend to result in significantly more bankruptcies associated to credit losses whereas lack of liquidity tends tobe the primary cause of failures under lower rates.

Journal article

Jensen HJ, Viegas E, Cockburn SP, West GBet al., 2014, The dynamics of mergers and acquisitions: ancestry as the seminal determinant, Proceedings of the Royal Society A: Mathematical, Physical & Engineering Sciences, Vol: 470, ISSN: 1471-2946

Journal article

Viegas E, Takayasu M, Miura W, Tamura K, Ohnishi T, Takayasu H, Jensen HJet al., 2013, Ecosystems Perspective on Financial Networks: Diagnostic Tools, COMPLEXITY, Vol: 19, Pages: 22-36, ISSN: 1076-2787

Journal article

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