187 research outputs found
On Computing Minimum Unsatisfiable Cores
Certifying the correctness of a SAT solver is straightforward for satisfiable instances of SAT. Given
A Hybrid Artificial Bee Colony Algorithm for Graph 3-Coloring
The Artificial Bee Colony (ABC) is the name of an optimization algorithm that
was inspired by the intelligent behavior of a honey bee swarm. It is widely
recognized as a quick, reliable, and efficient methods for solving optimization
problems. This paper proposes a hybrid ABC (HABC) algorithm for graph
3-coloring, which is a well-known discrete optimization problem. The results of
HABC are compared with results of the well-known graph coloring algorithms of
today, i.e. the Tabucol and Hybrid Evolutionary algorithm (HEA) and results of
the traditional evolutionary algorithm with SAW method (EA-SAW). Extensive
experimentations has shown that the HABC matched the competitive results of the
best graph coloring algorithms, and did better than the traditional heuristics
EA-SAW when solving equi-partite, flat, and random generated medium-sized
graphs
Extremal Optimization: Methods derived from Co-Evolution
We describe a general-purpose method for finding high-quality solutions to
hard optimization problems, inspired by self-organized critical models of
co-evolution such as the Bak-Sneppen model. The method, called Extremal
Optimization, successively eliminates extremely undesirable components of
sub-optimal solutions, rather than ``breeding'' better components. In contrast
to Genetic Algorithms which operate on an entire ``gene-pool'' of possible
solutions, Extremal Optimization improves on a single candidate solution by
treating each of its components as species co-evolving according to Darwinian
principles. Unlike Simulated Annealing, its non-equilibrium approach effects an
algorithm requiring few parameters to tune. With only one adjustable parameter,
its performance proves competitive with, and often superior to, more elaborate
stochastic optimization procedures. We demonstrate it here on two classic hard
optimization problems: graph partitioning and the traveling salesman problem.Comment: 8 pages, Latex, 5 ps-figures included. To appear in ``GECCO-99:
Proceedings of the Genetic and Evolutionary Computation Conference,'' (Morgan
Kaufmann, San Francisco, 1999
Extremal Optimization of Graph Partitioning at the Percolation Threshold
The benefits of a recently proposed method to approximate hard optimization
problems are demonstrated on the graph partitioning problem. The performance of
this new method, called Extremal Optimization, is compared to Simulated
Annealing in extensive numerical simulations. While generally a complex
(NP-hard) problem, the optimization of the graph partitions is particularly
difficult for sparse graphs with average connectivities near the percolation
threshold. At this threshold, the relative error of Simulated Annealing for
large graphs is found to diverge relative to Extremal Optimization at equalized
runtime. On the other hand, Extremal Optimization, based on the extremal
dynamics of self-organized critical systems, reproduces known results about
optimal partitions at this critical point quite well.Comment: 7 pages, RevTex, 9 ps-figures included, as to appear in Journal of
Physics
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