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The NK model is a mathematical model described by its primary inventor Stuart Kauffman as a "tunably rugged" fitness landscape. "Tunable ruggedness" captures the intuition that both the overall size of the landscape and the number of its local "hills and valleys" can be adjusted via changes to its two parameters, and , with being the length of a string of evolution and determining the level of landscape ruggedness.
The NK model has found application in a wide variety of fields, including the theoretical study of evolutionary biology, immunology, optimisation, technological evolution, team science,[1] and complex systems. The model was also adopted in organizational theory, where it is used to describe the way an agent may search a landscape by manipulating various characteristics of itself. For example, an agent can be an organization, the hills and valleys represent profit (or changes thereof), and movement on the landscape necessitates organizational decisions (such as adding product lines or altering the organizational structure), which tend to interact with each other and affect profit in a complex fashion.[2]
An early version of the model, which considered only the smoothest () and most rugged () landscapes, was presented in Kauffman and Levin (1987).[3] The model as it is currently known first appeared in Kauffman and Weinberger (1989).[4]
One of the reasons why the model has attracted wide attention in optimisation is that it is a particularly simple instance of a so-called NP-complete problem[5] which means it is difficult to find global optima. Recently, it was shown that the NK model for K > 1 is also PLS-complete[6] which means than, in general, it is difficult to find even local fitness optima. This has consequences for the study of open-ended evolution.
^Boroomand, Amin; Smaldino, Paul E. (2023). "Superiority bias and communication noise can enhance collective problem solving". Journal of Artificial Societies and Social Simulation. 26 (3). doi:10.18564/jasss.5154.
^Levinthal, D. A. (1997). "Adaptation on Rugged Landscapes". Management Science. 43 (7): 934–950. doi:10.1287/mnsc.43.7.934.
^Kauffman, S.; Levin, S. (1987). "Towards a general theory of adaptive walks on rugged landscapes". Journal of Theoretical Biology. 128 (1): 11–45. Bibcode:1987JThBi.128...11K. doi:10.1016/s0022-5193(87)80029-2. PMID 3431131.
^Kauffman, S.; Weinberger, E. (1989). "The NK Model of rugged fitness landscapes and its application to the maturation of the immune response". Journal of Theoretical Biology. 141 (2): 211–245. Bibcode:1989JThBi.141..211K. doi:10.1016/s0022-5193(89)80019-0. PMID 2632988.
^Weinberger, E. (1996), "NP-completeness of Kauffman's N-k model, a Tuneably Rugged Fitness Landscape", Santa Fe Institute Working Paper, 96-02-003.
^Kaznatcheev, Artem (2019). "Computational Complexity as an Ultimate Constraint on Evolution". Genetics. 212 (1): 245–265. doi:10.1534/genetics.119.302000. PMC 6499524. PMID 30833289.
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S2CID 26956345. Stoltzfus, A. (2006). "Mutation-Biased Adaptation in a Protein NKModel". Molecular Biology and Evolution. 23 (10): 1852–1862. doi:10.1093/molbev/msl064...
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S2CID 26956345. Stoltzfus, A. (2006). "Mutation-Biased Adaptation in a Protein NKModel". Molecular Biology and Evolution. 23 (10): 1852–1862. doi:10.1093/molbev/msl064...
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