Highly optimized tolerance

In applied mathematics, highly optimized tolerance (HOT) is a method of generating power law behavior in systems by including a global optimization principle. For some systems that display a characteristic scale, a global optimization term could potentially be added that would then yield power law behavior. It has been used to generate and describe internet-like graphs, forest fire models and may also apply to biological systems.

Example

The following is taken from Sornette's book.

Consider a random variable, $X$, that takes on values $x_{i}$ with probability $p_{i}$. Furthmore, lets assume for another parameter $r_{i}$

$x_{i}=r_{i}^{{-\beta }}$

for some fixed $\beta$. We then want to minimize

$L=\sum _{{i=0}}^{{N-1}}p_{i}x_{i}$

subject to the constraint

$\sum _{{i=0}}^{{N-1}}r_{i}=\kappa$

Using Lagrange multipliers, this gives

$p_{i}\propto x_{i}^{{-(1+1/\beta )}}$

giving us a power law. The global optimization of minimizing the energy along with the power law dependence between $x_{i}$ and $r_{i}$ gives us a power law distribution in probability.

See also

• self-organized criticality

References

• Carlson, J. M.; Doyle, John (August 1999), "Highly optimized tolerance: A mechanism for power laws in designed systems", Physical Review E, 60 (2): 1412–1427, doi:10.1103/PhysRevE.60.1412.
• Carlson, J. M.; Doyle, John (March 2000), "Highly Optimized Tolerance: Robustness and Design in Complex Systems", Physical Review Letters, 84 (11): 2529–2532, doi:10.1103/PhysRevLett.84.2529.
• Doyle, John; Carlson, J. M. (June 2000), "Power Laws, Highly Optimized Tolerance, and Generalized Source Coding", Physical Review Letters, 84 (24): 5656–5659, doi:10.1103/PhysRevLett.84.5656.
• Greene, Katie (2005), "Untangling a web: The internet gets a new look", Science News, 168 (15): 230–230, doi:10.2307/4016836.
• Li, Lun; Alderson, David; Doyle, John C.; Willinger, Walter (2005), "Towards a theory of scale-free graphs: definition, properties, and implications", Internet Mathematics, 2 (4): 431–523, arXiv:cond-mat/0501169, MR 2241756.
• Robert, Carl; Carlson, J. M.; Doyle, John (April 2001), "Highly optimized tolerance in epidemic models incorporating local optimization and regrowth", Physical Review E, 63 (5): 056122, doi:10.1103/PhysRevE.63.056122.
• Sornette, Didier (2000), Critical Phenomena in Natural Sciences: Chaos, Fractals, Selforganization and Disorder: Concepts and Tools, Springer Series in Synergetics, Berlin: Springer-Verlag, doi:10.1007/978-3-662-04174-1, ISBN 3-540-67462-4, MR 1782504.
• Zhou, Tong; Carlson, J. M. (2000), "Dynamics and changing environments in highly optimized tolerance", Physical Review E, 62: 3197–3204, doi:10.1103/PhysRevE.62.3197.
• Zhou, Tong; Carlson, J. M.; Doyle, John (2002), "Mutation, specialization, and hypersensitivity in highly optimized tolerance", Proceedings of the National Academy of Sciences, 99 (4): 2049–2054, doi:10.1073/pnas.261714399.