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29
On Network Correlated Data Gathering
 IN IEEE INFOCOM
, 2004
"... We consider the problem of correlated data gathering by a network with a sink node and a tree communication structure, where the goal is to minimize the total transmission cost of transporting the information collected by the nodes, to the sink node. Two coding strategies are analyzed: a SlepianWolf ..."
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Cited by 98 (9 self)
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We consider the problem of correlated data gathering by a network with a sink node and a tree communication structure, where the goal is to minimize the total transmission cost of transporting the information collected by the nodes, to the sink node. Two coding strategies are analyzed: a SlepianWolf model where optimal coding is complex and transmission optimization is simple, and a joint entropy coding model with explicit communication where coding is simple and transmission optimization is difficult. This problem requires a joint optimization of the rate allocation at the nodes and of the transmission structure. For the SlepianWolf setting, we derive a closed form solution and an efficient distributed approximation algorithm with a good performance. For the explicit communication case, we prove that building an optimal data gathering tree is NPcomplete and we propose various distributed approximation algorithms.
Problem Difficulty for Tabu Search in JobShop Scheduling
 Artificial Intelligence
, 2002
"... Tabu search algorithms are among the most effective approaches for solving the jobshop scheduling problem (JSP). Yet, we have little understanding of why these algorithms work so well, and under what conditions. We develop a model of problem difficulty for tabu search in the JSP, borrowing from sim ..."
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Cited by 20 (7 self)
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Tabu search algorithms are among the most effective approaches for solving the jobshop scheduling problem (JSP). Yet, we have little understanding of why these algorithms work so well, and under what conditions. We develop a model of problem difficulty for tabu search in the JSP, borrowing from similar models developed for SAT and other NP  complete problems. We show that the mean distance between random local optima and the nearest optimal solution is highly correlated with the cost of locating optimal solutions to typical, random JSPs. Additionally, this model accounts for the cost of locating suboptimal solutions, and provides an explanation for differences in the relative difficulty of square versus rectangular JSPs. We also identify two important limitations of our model. First, model accuracy is inversely correlated with problem difficulty, and is exceptionally poor for rare, very highcost problem instances. Second, the model is significantly less accurate for structured, nonrandom JSPs. Our results are also likely to be useful in future research on difficulty models of local search in SAT, as local search cost in both SAT and the JSP is largely dictated by the same search space features. Similarly, our research represents the first attempt to quantitatively model the cost of tabu search for any NP complete problem, and may possibly be leveraged in an effort to understand tabu search in problems other than jobshop scheduling.
On the Utility of Redundant Encodings in Mutationbased Evolutionary Search
 In
, 2002
"... A number of recent works in the evolutionary computation eld have suggested that introducing large amounts of genetic redundancy may increase the evolvability of a population in an evolutionary algorithm. These works have variously claimed that the reliability of the search, the nal tness achi ..."
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Cited by 14 (0 self)
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A number of recent works in the evolutionary computation eld have suggested that introducing large amounts of genetic redundancy may increase the evolvability of a population in an evolutionary algorithm. These works have variously claimed that the reliability of the search, the nal tness achieved, the ability to cope with changing environments, and the robustness to high mutation rates, may all be improved by employing this strategy. In this paper we dispute some of these claims, arguing that adding random redundancy cannot be generally useful for optimization purposes. By way of example we report on experiments where a proposed neutral encoding scheme (based on random Boolean networks) is compared to a direct encoding in two mutationonly EAs, at various mutation rates. Our ndings show that with the appropriate choice of perbit mutation rate, the evolvability of populations using the direct encoding is no less than with the redundant one.
Evolution on distributive lattices
 J Theor Biol
"... Abstract. We consider the directed evolution of a population after an intervention that has significantly altered the underlying fitness landscape. We model the space of genotypes as a distributive lattice; the fitness landscape is a realvalued function on that lattice. The risk of escape from inte ..."
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Cited by 10 (5 self)
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Abstract. We consider the directed evolution of a population after an intervention that has significantly altered the underlying fitness landscape. We model the space of genotypes as a distributive lattice; the fitness landscape is a realvalued function on that lattice. The risk of escape from intervention, i.e., the probability that the population develops an escape mutant before extinction, is encoded in the risk polynomial. Tools from algebraic combinatorics are applied to compute the risk polynomial in terms of the fitness landscape. In an application to the development of drug resistance in HIV, we study the risk of viral escape from treatment with the protease inhibitors ritonavir and indinavir.
QuasiIndependence, Homology and the Unity of Type: A Topological Theory of Characters
 J. Theor. Biol
"... In this paper Lewontin's notion of "quasiindependence" of characters is formalized as the assumption that a region of the phenotype space can be represented by a product space of orthogonal factors. In this picture each character corresponds to a factor of a region of the phenotype space. We consid ..."
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Cited by 10 (4 self)
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In this paper Lewontin's notion of "quasiindependence" of characters is formalized as the assumption that a region of the phenotype space can be represented by a product space of orthogonal factors. In this picture each character corresponds to a factor of a region of the phenotype space. We consider any region of the phenotype space that has a given factorization as a "type", i.e., as a set of phenotypes that share the same set of phenotypic characters. Using the notion of local factorizations we develop a theory of character identity based on the continuity of common factors among di#erent regions of the phenotype space. We also consider the topological constraints on evolutionary transitions among regions with di#erent regional factorizations, i.e., for the evolution of new types or body plans. It is shown that direct transition between di#erent "types" is only possible if the transitional forms have all the characters that the ancestral and the derived types have and are thus compatible with the factorization of both types. Transitional forms thus have to go over a "complexity hump" where they have more quasiindependent characters than either the ancestral as well as the derived type. The only logical, but biologically unlikely, alternative is a "hopeful monster" that transforms in a single step from the ancestral type to the derived type. Topological considerations also suggest a new factor that may contribute to the evolutionary stability of "types." It is shown that if the type is decomposable into factors which are vertex irregular (i.e. have states that are more or less preferred in a random walk), the region of phenotypes representing the type contains islands of strongly preferred states. In other words types have a statistical tendency of retaining evolu...
An Efficient Local Search Method for Random 3Satisfiability
, 2003
"... We report on some exceptionally good results in the solution of randomly generated 3satisfiability instances using the "recordtorecord travel (RRT)" local search method. When this simple, but lessstudied algorithm is applied to random onemillion variable instances from the problem's satisfiable ..."
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Cited by 7 (4 self)
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We report on some exceptionally good results in the solution of randomly generated 3satisfiability instances using the "recordtorecord travel (RRT)" local search method. When this simple, but lessstudied algorithm is applied to random onemillion variable instances from the problem's satisfiable phase, it seems to find satisfying truth assignments almost always in linear time, with the coefficient of linearity depending on the ratio α of clauses to variables in the generated instances. RRT has a parameter for tuning "greediness". By lessening greediness, the linear time phase can be extended up to very close to the satisfiability threshold α_c. Such linear time complexity is typical for randomwalk based local search methods for small values of α. Previously, however, it has been suspected that these methods necessarily lose their time linearity far below the satisfiability threshold. The only previously introduced algorithm reported to have nearly linear time complexity also close to the satisfiability threshold is the survey propagation (SP) algorithm. However, SP is not a local search method and is more complicated to implement than RRT. Comparative experiments with the WalkSAT local search algorithm show behavior somewhat similar to RRT, but with the linear time phase not extending quite as close to the satisfiability threshold.
Almost Tight Upper Bound for Finding Fourier Coefficients of Bounded PseudoBoolean Functions
"... 1 ..."
Inbreeding properties of geometric crossover and nongeometric recombinations
 In Proceedings of the Foundations of Genetic Algorithms
, 2007
"... Abstract. Geometric crossover is a representationindependent generalization of traditional crossover for binary strings. It is defined using the distance associated to the search space in a simple geometric way. Many interesting recombination operators for the most frequently used representations a ..."
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Cited by 5 (4 self)
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Abstract. Geometric crossover is a representationindependent generalization of traditional crossover for binary strings. It is defined using the distance associated to the search space in a simple geometric way. Many interesting recombination operators for the most frequently used representations are geometric crossovers under some suitable distance. Being a geometric crossover is useful because there is a growing number of theoretical results that apply to this class of operators. To show that a given recombination operator is a geometric crossover, it is sufficient to find a distance for which offspring are in the metric segment between parents associated with this distance. However, proving that a recombination operator is not a geometric crossover requires to prove that such an operator is not a geometric crossover under any distance. In this paper we develop some theoretical tools to prove nongeometricity results and show that some wellknown operators are not geometric. 1