Search results for " nonlinear dynamical systems"

showing 3 items of 3 documents

Asymptotic regime in N random interacting species

2005

The asymptotic regime of a complex ecosystem with \emph{N}random interacting species and in the presence of an external multiplicative noise is analyzed. We find the role of the external noise on the long time probability distribution of the i-th density species, the extinction of species and the local field acting on the i-th population. We analyze in detail the transient dynamics of this field and the cavity field, which is the field acting on the $i^{th}$ species when this is absent. We find that the presence or the absence of some population give different asymptotic distributions of these fields.

Fluctuation phenomena random processes noise and Brownian motionPhysicsPhysics - Physics and SocietyFluctuation phenomena random processes noise and Brownian motion; Nonlinear dynamics and nonlinear dynamical systems; Population dynamics and ecological pattern formation; Complex Systemseducation.field_of_studySettore FIS/02 - Fisica Teorica Modelli E Metodi MatematiciExtinctionField (physics)PopulationFOS: Physical sciencesComplex SystemsPhysics and Society (physics.soc-ph)External noiseCondensed Matter PhysicsComplex ecosystemMultiplicative noiseElectronic Optical and Magnetic MaterialsProbability distributionQuantitative Biology::Populations and EvolutionStatistical physicsNonlinear dynamics and nonlinear dynamical systemeducationLocal fieldComputer Science::Distributed Parallel and Cluster ComputingPopulation dynamics and ecological pattern formation
researchProduct

Moment Equations for a Spatially Extended System of Two Competing Species

2005

The dynamics of a spatially extended system of two competing species in the presence of two noise sources is studied. A correlated dichotomous noise acts on the interaction parameter and a multiplicative white noise affects directly the dynamics of the two species. To describe the spatial distribution of the species we use a model based on Lotka-Volterra (LV) equations. By writing them in a mean field form, the corresponding moment equations for the species concentrations are obtained in Gaussian approximation. In this formalism the system dynamics is analyzed for different values of the multiplicative noise intensity. Finally by comparing these results with those obtained by direct simulat…

PhysicsFluctuation phenomena random processes noise and Brownian motionSettore FIS/02 - Fisica Teorica Modelli E Metodi MatematiciStatistical Mechanics (cond-mat.stat-mech)Multiplicative white noiseFOS: Physical sciencesFluctuation phenomena random processes noise and Brownian motion; Nonlinear dynamics and nonlinear dynamical systems; Population dynamics and ecological pattern formationCondensed Matter PhysicsSpatial distributionMultiplicative noiseElectronic Optical and Magnetic MaterialsSystem dynamicsMean field theorySpatial ecologyQuantitative Biology::Populations and EvolutionStatistical physicsNonlinear dynamics and nonlinear dynamical systemCondensed Matter - Statistical MechanicsMoment equationsCoupled map latticePopulation dynamics and ecological pattern formation
researchProduct

System identification via optimised wavelet-based neural networks

2003

Nonlinear system identification by means of wavelet-based neural networks (WBNNs) is presented. An iterative method is proposed, based on a way of combining genetic algorithms (GAs) and least-square techniques with the aim of avoiding redundancy in the representation of the function. GAs are used for optimal selection of the structure of the WBNN and the parameters of the transfer function of its neurones. Least-square techniques are used to update the weights of the net. The basic criterion of the method is the addition of a new neurone, at a generic step, to the already constructed WBNN so that no modification to the parameters of its neurones is required. Simulation experiments and compa…

least squares approximations nonlinear dynamical systems identification neural nets iterative methods genetic algorithmsQuantitative Biology::Neurons and CognitionArtificial neural networkNonlinear system identificationIterative methodComputer scienceSystem identificationTransfer functionWaveletSettore ING-INF/04 - AutomaticaControl and Systems EngineeringControl theoryRedundancy (engineering)Electrical and Electronic EngineeringRepresentation (mathematics)InstrumentationAlgorithmIEE Proceedings - Control Theory and Applications
researchProduct