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Dragon king (DK) is double metaphor for an event that is both extremely large in size or impact (a "king") and born of unique origins (a "dragon") relative to its peers (other events from the same system). DK events are generated by / correspond to mechanisms such as positive feedback, tipping points, bifurcations, and phase transitions, that tend to occur in nonlinear and complex systems, and serve to amplify DK events to extreme levels. By understanding and monitoring these dynamics, some predictability of such events may be obtained. 〔Sornette, Didier, and Guy Ouillon. "Dragon-kings: mechanisms, statistical methods and empirical evidence." The European Physical Journal Special Topics 205.1 (2012): 1-26.〕 〔D. Sornette, Dragon-Kings, Black Swans and the Prediction of Crises, International Journal of Terraspace Science and Engineering 1(3), 1-17 (2009) (http://arXiv.org/abs/0907.4290) and (http://ssrn.com/abstract=1470006)〕 〔D. Sornette, Predictability of catastrophic events: material rupture, earthquakes, turbulence, financial crashes and human birth, Prof. Nat. Acad. Sci. USA 99, SUPP1 (2002) 2522-2529〕 The theory has been developed by Prof. Didier Sornette, who hypothesizes that many of the crises that we face are in fact DK rather than black swans—i.e., they may be predictable to some degree. Given the importance of crises to the long-term organization of a variety of systems, the DK theory urges that special attention be given to the study and monitoring of extremes, and that a dynamic view be taken. From a scientific viewpoint, such extremes are interesting because they may reveal underlying, often hidden, organizing principles. Practically speaking, one should ambitiously study extreme risks, but not forget that significant uncertainty will almost always be present, and should be rigorously considered in decisions regarding risk management and design. The theory of DK is related to concepts such as: black swan theory, outliers, complex systems, nonlinear dynamics, power laws, extreme value theory, prediction, extreme risks, risk management, etc. ==Black swans and dragon kings== Black swan can be considered a metaphor for an event that is surprising (to the observer), has a major effect, and, after being observed, is rationalized in hindsight. The theory of black swans is epistemological, relating to the limited knowledge and understanding of the observer. The term was introduced and popularized by Nassim Taleb and has been associated with concepts such as heavy tails, non-linear payoffs, model error, and even Knightian uncertainty, whose “unknowable unknown” event terminology was popularized by former United States Secretary of Defence Donald Rumsfeld. Taleb claims that black swan events are not predictable, and in practice, the theory encourages one to “prepare rather than predict”, and limit ones exposure to extreme fluctuations. The black swan concept is important and poses a valid criticism of people, firms, and societies that are irresponsible in the sense that they are overly confident in their ability to anticipate and manage risk. However, claiming that extreme events are – in general – unpredictable may also lead to a lack of accountability in risk management roles. In fact, it is known that in a wide range of physical systems that extreme events are predictable to some degree 〔Didier Sornette TED Talk: https://www.ted.com/talks/didier_sornette_how_we_can_predict_the_next_financial_crisis?language=en〕 〔Albeverio, Sergio, Volker Jentsch, and Holger Kantz. Extreme events in nature and society. Springer Science & Business Media, 2006.〕 .〔〔 One simply needs to have a sufficiently deep understanding of the structure and dynamics of the focal system, and the ability to monitor it. This is the domain of the dragon kings. Such events have been referred to as Grey Swans by Taleb. A more rigorous distinction between black swans, grey swans, and dragon kings is difficult as black swans are not precisely defined in physical and mathematical terms. However technical elaboration of concepts in the Black Swan book are elaborated in the (Silent Risk ) document. An analysis of the precise definition of a black swan in a risk management context was written by Prof. Terje Aven〔Aven, Terje. "On the meaning of a black swan in a risk context." Safety science 57 (2013): 44-51.〕 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Dragon King Theory」の詳細全文を読む スポンサード リンク
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