Browsing by Author "Onnela, Jukka-Pekka"
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Item Complex networks in the study of financial and social systems(Helsinki University of Technology, 2006-07-10) Onnela, Jukka-Pekka; Department of Electrical and Communications Engineering; Sähkö- ja tietoliikennetekniikan osasto; Laboratory of Computational Engineering; Laskennallisen tekniikan laboratorio; Kaski, Kimmo; Acad. Prof.Complex systems consist of a large number of interacting elements, giving rise to the emergence of organisation without any external organising principle being applied. Consequently, decomposing the system and studying its subparts in isolation does not contribute to our understanding of how it works. Fortunately, complex systems can be described, analysed, and modelled using complex networks. Here one focuses only on the elements and topology of interactions between them, providing a system-level perspective to the system under study. This thesis contributes to the network approach to complex systems in two ways. First, using empirical data on the financial market, we show how a general problem dealing with correlated actors can be recast as a network problem. In principle, this simple method is applicable to any complex system with temporal correlations of quantities attached to each element. In the context of social systems we demonstrate how a network model of social actors can be constructed to capture the hypothesised structure of interactions. Using the rate equation approach, we develop a simple phenomenological model intended for future study of processes unfolding on social networks. Second, we develop generalisable methods and measures for network characterisation. These measures are not too application specific so they can be transferred to disparate complex systems. For example, we augment the motif framework to incorporate interaction strengths, enabling us to go beyond topology and account for the heterogeneity of interactions. The studied complex systems can be classified broadly as financial and social systems. As data rich systems they enable a thorough testing of the developed concepts. In addition, they have numerous applications within the complex systems paradigm, including developing better risk management schemes and enabling in silico testing of different disease immunisation scenarios. The focus of this thesis lies in the universal aspects of these systems; the line of enquiry is to motivate a question in one system, then step back and see if the machinery developed to tackle the problem has relevance to other systems. In addition to conceptual developments, we provide tools for characterising complex networks in practice.Item Taxonomy of Financial Assets(2002) Onnela, Jukka-Pekka; Chakraborti, Anirban; Sähkö- ja tietoliikennetekniikan osasto; Teknillinen korkeakoulu; Helsinki University of Technology; Kaski, Kimmo
