2,157 research outputs found
Time walkers and spatial dynamics of ageing information
The distribution of information is essential for living system's ability to
coordinate and adapt. Random walkers are often used to model this distribution
process and, in doing so, one effectively assumes that information maintains
its relevance over time. But the value of information in social and biological
systems often decay and must continuously be updated. To capture the spatial
dynamics of ageing information, we introduce time walkers. A time walker moves
like a random walker, but interacts with traces left by other walkers, some
representing older information, some newer. The traces forms a navigable
information landscape. We quantify the dynamical properties of time walkers
moving on a two-dimensional lattice and the quality of the information
landscape generated by their movements. We visualise the self-similar landscape
as a river network, and show that searching in this landscape is superior to
random searching and scales as the length of loop-erased random walks
Synchronization in Weighted Uncorrelated Complex Networks in a Noisy Environment: Optimization and Connections with Transport Efficiency
Motivated by synchronization problems in noisy environments, we study the
Edwards-Wilkinson process on weighted uncorrelated scale-free networks. We
consider a specific form of the weights, where the strength (and the associated
cost) of a link is proportional to with and
being the degrees of the nodes connected by the link. Subject to the
constraint that the total network cost is fixed, we find that in the mean-field
approximation on uncorrelated scale-free graphs, synchronization is optimal at
-1. Numerical results, based on exact numerical diagonalization
of the corresponding network Laplacian, confirm the mean-field results, with
small corrections to the optimal value of . Employing our recent
connections between the Edwards-Wilkinson process and resistor networks, and
some well-known connections between random walks and resistor networks, we also
pursue a naturally related problem of optimizing performance in queue-limited
communication networks utilizing local weighted routing schemes.Comment: Papers on related research can be found at
http://www.rpi.edu/~korniss/Research
Distributed flow optimization and cascading effects in weighted complex networks
We investigate the effect of a specific edge weighting scheme on distributed flow efficiency and robustness to cascading
failures in scale-free networks. In particular, we analyze a simple, yet
fundamental distributed flow model: current flow in random resistor networks.
By the tuning of control parameter and by considering two general cases
of relative node processing capabilities as well as the effect of bandwidth, we
show the dependence of transport efficiency upon the correlations between the
topology and weights. By studying the severity of cascades for different
control parameter , we find that network resilience to cascading
overloads and network throughput is optimal for the same value of over
the range of node capacities and available bandwidth
Comparision of the walk techniques for fitness state space analysis in vehicle routing problem
The Vehicle Routing Problem (VRP) is a highly researched discrete optimization task. The first article dealing with this problem was published by Dantzig and Ramster in 1959 under the name Truck Dispatching Problem. Since then, several versions of VRP have been developed. The task is NP difficult, it can be solved only in the foreseeable future, relying on different heuristic algorithms. The geometrical property of the state space influences the efficiency of the optimization method. In this paper, we present an analysis of the following state space methods: adaptive, reverse adaptive and uphill-downhill walk. In our paper, the efficiency of four operators are analysed on a complex Vehicle Routing Problem. These operators are the 2-opt, Partially Matched Crossover, Cycle Crossover and Order Crossover. Based on the test results, the 2-opt and Partially Matched Crossover are superior to the other two methods
What Could / Should YOUR “Urban Village” be (like) ?
This presentation is an expanded version of an invited input contribution to the Ouseburn Management Board in one of closed their strategy meeting earlier in May of that year.
It looks critiaclly and the concept of "urban villages", how this might apply to the (Lower) Ousburn Valley, and how the community and its various player themselves could devise a process to explore a clearer understanding and positioning vis-a-vis the applicability and usefulness of this concept for their locality, on their terms
A Methodology for Classifying Search Operators as Intensification or Diversification Heuristics
Selection hyper-heuristics are generic search tools that dynamically choose, from a given pool, the most promising operator (low-level heuristic) to apply at each iteration of the search process. The performance of these methods depends on the quality of the heuristic pool. Two types of heuristics can be part of the pool: diversification heuristics, which help to escape from local optima, and intensification heuristics, which effectively exploit promising regions in the vicinity of good solutions. An effective search strategy needs a balance between these two strategies. However, it is not straightforward to categorize an operator as intensification or diversification heuristic on complex domains. Therefore, we propose an automated methodology to do this classification. This brings methodological rigor to the configuration of an iterated local search hyper-heuristic featuring diversification and intensification stages. The methodology considers the empirical ranking of the heuristics based on an estimation of their capacity to either diversify or intensify the search. We incorporate the proposed approach into a state-of-the-art hyper-heuristic solving two domains: course timetabling and vehicle routing. Our results indicate improved performance, including new best-known solutions for the course timetabling problem
Identifying communities by influence dynamics in social networks
Communities are not static; they evolve, split and merge, appear and
disappear, i.e. they are product of dynamical processes that govern the
evolution of the network. A good algorithm for community detection should not
only quantify the topology of the network, but incorporate the dynamical
processes that take place on the network. We present a novel algorithm for
community detection that combines network structure with processes that support
creation and/or evolution of communities. The algorithm does not embrace the
universal approach but instead tries to focus on social networks and model
dynamic social interactions that occur on those networks. It identifies
leaders, and communities that form around those leaders. It naturally supports
overlapping communities by associating each node with a membership vector that
describes node's involvement in each community. This way, in addition to
overlapping communities, we can identify nodes that are good followers to their
leader, and also nodes with no clear community involvement that serve as a
proxy between several communities and are equally as important. We run the
algorithm for several real social networks which we believe represent a good
fraction of the wide body of social networks and discuss the results including
other possible applications.Comment: 10 pages, 6 figure
Simulation-based fitness landscape analysis and optimisation of complex problems
Widespread hard optimisation problems in economics and logistics are characterised by large dimensions, uncertainty and nonlinearity and require more powerful methods of stochastic optimisation that traditional ones. Simulation optimisation is a powerful tool for solving these problems. Moreover, fitness landscape analysis techniques provide an efficient approach to better selection of a suitable optimisation algorithm. The concept and techniques of fitness landscape analysis are described. A formalised scheme for simulation optimisation enhanced with fitness landscape analysis is given. Benchmark fitness landscape analysis is performed to find relations between efficiency of an optimisation algorithm and structural features of a fitness landscape. Case study in simulation optimisation of vehicle routing and scheduling is described. Various optimisation scenarios with application of the fitness landscape analysis are discussed and investigated
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