Precise influence evaluation in complex networks

Evaluating node influence is fundamental for identifying key nodes in complex networks. Existing methods typically rely on generic indicators to rank node influence across diverse networks, thereby ignoring the individualized features of each network itself. Actually, node influence stems not only from general features but the multi-scale individualized information encompassing specific network structure and task. Here we design an active learning architecture to predict node influence quantitively and precisely, which samples representative nodes based on graph entropy correlation matrix integrating multi-scale individualized information. This brings two intuitive advantages: (1) discovering potential high-influence but weak-connected nodes that are usually ignored in existing methods, (2) improving the influence maximization strategy by deducing influence interference. Significantly, our architecture demonstrates exceptional transfer learning capabilities across multiple types of networks, which can identify those key nodes with large disputation across different existing methods. Additionally, our approach, combined with a simple greedy algorithm, exhibits dominant performance in solving the influence maximization problem. This architecture holds great potential for applications in graph mining and prediction tasks

Management of Foreign Reserves: An Approach Based on Vine-Copula, Regime-Switching Dependence and Bayesian Opinion Pooling

This research is constructed to address the issue of structure management for colossal foreign exchange reserves holders, such as China and other emerging economies. Contrary to the discussion of optimal quantity on the reserve level, structure management considers the ideal applications of the national wealth, specifically the compositions in the reserves' financial investments. Two perspectives are considered for the safety and liquidity tranche of the foreign reserves, and another one for the return tranche. The thwo perspectives are further developed into three chapters of this thesis and they form a comprehensive set of analyses for the structure management. First, the optimal currency composition for huge foreign reserves in the safety and liquidity tranche is investigated. The asymmetry fat-tails and complex dependence structure in distributions of currency returns are examined for their vital role in the portfolio risk appraisal. In a D-vine copula approach, it is shown that under the disappointment aversion effect, the central bank in our model can achieve sizeable gains in economic value by switching from the mean-variance to copula modelling. It is also found that this approach will lead to an optimal currency composition that allows China to have more space for international currency diversification, while maintaining the leading position of the US dollar in the currency shares of China’s reserves. Next, the strategic asset allocation for China’s foreign reserves in the same safety tranche is studied using a risk-based approach. Four aspects of the risk management are investigated: investment universe, dependence structure, allocation strategies under risk minimization and trade-off between risks and returns. A regime-switching copula model is developed to investigate the dynamic dependence between assets. The optimal allocation is derived following two strategies: risk minimization and trade-off between risk and returns in utility maximization with disappointment avoidance. If the central bank focuses solely on risk minimization, the asymmetries in the asset return dependence encourage the flight to safety. However, if higher risks are allowed in exchange for higher returns, even if the exchange is very conservative, the asymmetries would discourage the flight to safety. Therefore, we suggest that China should mitigate its flight to safety after 2008 and increase holdings of short-term bank deposits, long-term treasury bonds and euro bonds. Finally, the strategic asset allocation problem for China's Sovereign Wealth Fund, the China Investment Corporation, is examined. This is considered to be the return tranche of China's foreign reserves. Bearing the responsibility to pursue higher returns for China's huge volume of foreign exchange reserves, the China Investment Corporation is endowed with a capable funding position. However, its emphasis on safety is still considered more serious than that of other institutional investors. A new method combining the merits of the shrinkage estimation, vine-copula structure, and Black-Litterman model, is proposed and tested to satisfy the revealed investment objectives. Empirical analysis suggests that there is more emphasis on emerging market economies rather than advanced economies when diversifying in fixed-income securities; whereas that emphasis is reversed on the equities side. In addition, using the commodity ETFs to represent the significance of gold in the portfolio, it is discovered that gold is a formidable competitor to the investment in equities

Recommender Systems

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 and comparison of different approaches are lacking, which impedes further advances. In this article, we review recent developments in recommender systems and discuss the major challenges. We compare and evaluate available algorithms and examine their roles in the future developments. In addition to algorithms, physical aspects are described to illustrate macroscopic behavior of recommender systems. Potential impacts and future directions are discussed. We emphasize that recommendation has a great scientific depth and combines diverse research fields which makes it of interests for physicists as well as interdisciplinary researchers.Comment: 97 pages, 20 figures (To appear in Physics Reports

Transacciones basadas en información privilegiada y conducción empresarial en América Latina

(Disponible en idioma inglés únicamente) A diferencia de los inversionistas externos, los grupos de control tienen la opción de realizar transacciones basadas en información privilegiada y pueden ejercerla a costa de los inversionistas externos. En este trabajo se calculan las probabilidades de realización de transacciones informadas (ITP, por sus siglas en inglés) para el universo de acciones líquidas de siete países latinoamericanos que se negocian tanto en el país de origen como en ADR, y se aplica la ITP para dar respuesta a preguntas sobre la conducción empresarial. Se halló una heterogeneidad considerable de las ITP dentro de un entorno institucional. No obstante, se identificaron diferencias significativas de la ITP media entre gamas de volumen, países y tipos de título valor. La ITP guarda una correlación intuitivamente llamativa con algunas de las variables de protección de inversionistas en el ámbito nacional que se emplean en la obra publicada (no con todas). Se hallaron incrementos considerables de la ITP justo antes de efectuarse anuncios empresariales públicos, lo que sugiere que hay agentes informados privadamente que están explotando su privilegio cuando existe la posibilidad de obtener su mayor valor. La ITP adquiere su valor en el mercado: las compañías con mayor ITP registran un menor coeficiente de Tobin. Se concluye que el mercado parece reconocer y valorar acordemente las variables sustitutivas no observables de la probabilidad de realización de transacciones informadas (ITP) de la calidad de la conducción empresarial, tal como la heterogeneidad del comportamiento de la empresa.

Reconstructing networks

Complex networks datasets often come with the problem of missing information: interactions data that have not been measured or discovered, may be affected by errors, or are simply hidden because of privacy issues. This Element provides an overview of the ideas, methods and techniques to deal with this problem and that together define the field of network reconstruction. Given the extent of the subject, we shall focus on the inference methods rooted in statistical physics and information theory. The discussion will be organized according to the different scales of the reconstruction task, that is, whether the goal is to reconstruct the macroscopic structure of the network, to infer its mesoscale properties, or to predict the individual microscopic connections.Comment: 107 pages, 25 figure

Reconstructing networks

Complex networks datasets often come with the problem of missing information: interactions data that have not been measured or discovered, may be affected by errors, or are simply hidden because of privacy issues. This Element provides an overview of the ideas, methods and techniques to deal with this problem and that together define the field of network reconstruction. Given the extent of the subject, the authors focus on the inference methods rooted in statistical physics and information theory. The discussion is organized according to the different scales of the reconstruction task, that is, whether the goal is to reconstruct the macroscopic structure of the network, to infer its mesoscale properties, or to predict the individual microscopic connections

EVIDENCIAÇÃO DO RISCO EMPRESARIAL E AMBIENTAL DIANTE DAS MUDANÇAS CLIMÁTICAS E DO AQUECIMENTO GLOBAL

This paper is aimed at identifying economic and environmental evidence related to strategic risk caused by global climate change issues. To achieve this objective, descriptive and exploratory research was carried out, in the form of a case study, aiming to delimit the variables observed, the geographic area and the result of their possible interactions, in the context of a large company in the Brazilian hydroelectric energy industry. To characterize the importance of adapting its strategic planning in light of possible impacts from global climate changes, the Expert Panel, the Delphi Method and the SWOT Matrix were used as research techniques. The combined use of these three methods permitted further refinement of the research including the construction of long-term scenarios that could be inferred with regards to the research questions. The results obtained demonstrate that the reduction of water flow and reservoir levels, due to climate change, represent the main strategic environmental risks for the company being researched, which could threaten its corporate competitiveness and negatively compromise its operational, economic, and social performance until the year 2050.Este artigo tem como objetivo identificar evidências econômicas e ambientais em relação ao risco estratégico, por causa dos problemas das mudanças climáticas globais. Para isso realizou-se uma pesquisa descritiva-exploratória, conduzida através de um estudo de caso, visando delimitar as variáveis observadas, a área geográfica e o resultado de suas possíveis interações com o contexto de uma grande empresa da indústria de energia hidrelétrica brasileira. Para caracterizar a importância da adaptação de seu planejamento estratégico diante dos possíveis impactos das mudanças climáticas globais, empregou-se o Painel de Especialistas, o Método Delphi e a Matriz SWOT como técnicas de pesquisa. A utilização conjunta dessas três metodologias possibilitou um maior refinamento da pesquisa, com a construção de cenários de longo prazo que puderam ser inferidos em relação às questões pertinentes ao estudo. Os resultados obtidos mostram que a diminuição da vazão de água e a redução do nível dos reservatórios, devido às alterações climáticas, representam os principais riscos ambientais estratégicos da empresa estudada, podendo ameaçar sua competitividade empresarial e comprometer negativamente seu desempenho operacional, econômico e social até o ano de 2050

A critical reinterpretation of Shacklean decision theory

Shackle was one of the representative critics of probability calculus. His alternative decision theory was mathematically reformalized by Katzner till 1990s. Following the Katzner’s reformalized framework, this paper presents a new interpretation of Shacklean theory by focusing on the common stage structure of the decision-making. This paper shows that the characteristics of Shackle-Katzner framework can be explained as: (1) the non-distributive and non-additive ordinal measure of subjective uncertainty, (2) the incomplete list of imaginable future states, (3) the valuation of “importance” reflecting various types of loss- psychology, and (4) the final choice of the action is made on the set of importance intervals. The purpose of this paper is to investigate how the foundational stance of Shackle-Katzner framework about the decision-making elicits the different formal structure, and to provide a new interpretation of Shacklean decision theory