5 research outputs found
Spatially Compact Solutions and Stabilization in Einstein-Yang-Mills-Higgs Theories
New solutions to the static, spherically symmetric Einstein-Yang-Mills-Higgs
equations with the Higgs field in the triplet resp. doublet representation are
presented. They form continuous families parametrized by
( resp. denoting the W-boson resp. the Planck mass). The
corresponding spacetimes are regular and have spatially compact sections. A
particularly interesting class with the Yang-Mills amplitude being nodeless is
exhibited and is shown to be linearly stable with respect to spherically
symmetric perturbations. For some solutions with nodes of the Yang-Mills
amplitude a new stabilization phenomenon is found, according to which their
unstable modes disappear as increases (for the triplet) or decreases
(for the doublet).Comment: 7 pages, 4 figure
A modular modelling framework for hypotheses testing in the simulation of urbanisation
In this paper, we present a modelling experiment developed to study systems
of cities and processes of urbanisation in large territories over long time
spans. Building on geographical theories of urban evolution, we rely on
agent-based models to 1/ formalise complementary and alternative hypotheses of
urbanisation and 2/ explore their ability to simulate observed patterns in a
virtual laboratory. The paper is therefore divided into two sections : an
overview of the mechanisms implemented to represent competing hypotheses used
to simulate urban evolution; and an evaluation of the resulting model
structures in their ability to simulate - efficiently and parsimoniously - a
system of cities (the Former Soviet Union) over several periods of time (before
and after the crash of the USSR). We do so using a modular framework of
model-building and evolutionary algorithms for the calibration of several model
structures. This project aims at tackling equifinality in systems dynamics by
confronting different mechanisms with similar evaluation criteria. It enables
the identification of the best-performing models with respect to the chosen
criteria by scanning automatically the parameter along with the space of model
structures (as combinations of modelled dynamics).Comment: 21 pages, 3 figures, working pape
OpenMOLE, a workflow engine specifically tailored for the distributed exploration of simulation models
International audienceComplex-systems describe multiple levels of collective structure and organization. In such systems, the emergence of global behaviour from local interactions is generally studied through large scale experiments on numerical models. This analysis generates important computation loads which require the use of multi-core servers, clusters or grid computing. Dealing with such large scale executions is especially challenging for modellers who don't possess the theoretical and methodological skills required to take advantage of high performance computing environments. That's why we have designed a cloud approach for model experimentation. This approach has been implemented in OpenMOLE (Open MOdel Experiment) as a Domain Specific Language (DSL) that leverages the naturally parallel aspect of model experiments. The OpenMOLE DSL has been designed to explore user-supplied models. It delegates transparently their numerous executions to remote execution environment. From a user perspective, those environments are viewed as services providing computing power, therefore no technical detail is ever exposed. This paper presents the OpenMOLE DSL through the example of a toy model exploration and through the automated calibration of a real-world complex system model in the field of geography
Algorithmes évolutionnaires sur grille de calcul pour le calibrage de modéles géographiques
Sciences complexes n'est pas trĂšs heureux comme nom. Il serait mieux d'appeler cette discipline, science du complexe ou encore mieux systĂšmes complexes.As dynamic geographic models integrate very large number of spatial interactions, large amount of computing is necessaryfor their simulation and calibration, in order to validate them. Here a new automated calibration procedure is experimented onthe European computational grid EGI using evolutionnary algorithms. The application to the Simpoplocal model enables toreduce the computing time (one week) for managing about 7 millions runs for a preliminary validating step of the processesand parameters introduced in the model
Retour d'expérience de l'école OpenMOLE "ExModelo", organisée en partenariat avec le méso-centre du CRIANN
International audienceOpenMOLE (Reuillon et al., 2013) est une plateforme dâexploration automatique de modĂšles numĂ©riques. Elle permet dâĂ©tudier des programmes dĂ©veloppĂ©s dans une trĂšs large gamme de langages. OpenMOLE permet aussi de distribuer la charge de calcul sur la plupart des environnements de calcul (serveur, clusters, grille de calcul, cloud). La description de ces expĂ©riences sont dĂ©crits Ă lâaide DSL Ă destination dâutilisateurs non-informaticiens et non-spĂ©cialistes des environnements HPC. Alors que cette plateforme fĂȘte sa 10Ăšme release saluĂ© par une communautĂ© dâutilisateur en forte croissance, un nouveau pas vient dâĂȘtre franchi avec lâorganisation en 2019 dâune premiĂšre Ă©cole dâĂ©tĂ© dĂ©diĂ©e Ă âlâexploration de modĂšlesâ. Durant la formation, la plateforme et lâĂ©cosystĂšme de mĂ©thodes dâexploration qui lâaccompagne sont utilisĂ©s de maniĂšre intensive. Les travaux pratiques mettent en oeuvre lâexploration dâun modĂšle âjouetâ de dynamiques complexes dĂ©veloppĂ© pour lâoccasion. Il sâagit dâun modĂšle multi-agent spatialisĂ© de type proie/prĂ©dateur sur la thĂ©matique des zombies. Les apprenants pourront dĂ©couvrir lâusage et la spĂ©cificitĂ© de chacune des mĂ©thodes dâexplorations intĂ©grĂ©s dans la plateforme de façon interactive : analyses de sensibilitĂ© (Saltelli, Morris), calibrage et optimisation (Profiles, NSGA2, ABC), diversitĂ© (PSE). Lors des deux derniers jours, les participants sont invitĂ©s Ă formuler des questions sur le modĂšle de Zombies et Ă en proposer une Ă©tude en utilisant les outils dĂ©couverts les jours prĂ©cĂ©dents. La mise en oeuvre rapide de ces mĂ©thodes nâĂ©tant possible quâavec lâappui dâun environnement HPC, un partenariat avec lâUMR IDEES et le mĂ©so-centre Normand du CRIANN a Ă©tĂ© mis en place pour assurer un accĂšs rapide aux ressources de calcul nĂ©cessaires (1000 coeurs / 25 participants) pour les explorations menĂ©es pendant les 5 jours dâĂ©cole. DĂ©veloppĂ© avant tout pour accĂ©der Ă des ressources de type grille, OpenMOLE sâest constamment adaptĂ© pour offrir des connecteurs capable de suivre lâoffre croissante et trĂšs diversifiĂ©e en environnements de calcul. Il sâagit dâajouter Ă la fois des nouveaux connecteurs (PBS, SLURM, etc.) mais aussi de nouveaux moyens dâencapsulation et de dĂ©ploiement des programmes utilisateurs (Kubernetes, UDocker, PRoot, etc.). La collaboration entre les deux Ă©quipes du CRIANN et dâOpenMOLE sâinscrit dans ce cadre. BĂ©nĂ©fique pour les deux parties, elle a permis de soulever et rĂ©soudre des points de blocages reprĂ©sentatifs des diversitĂ©s de pratiques qui peuvent exister sur le plan matĂ©riel et logiciels (Fortran/C vs Java/R/Python) entre les deux communautĂ©s (Grille / Cluster). Dans cette prĂ©sentation nous proposons de faire une synthĂšse des rĂ©sultats obtenus par les groupes sur le modĂšle jouet, ainsi quâun retour sur cette collaboration originale entre les deux Ă©quipes techniques dâOpenMOLE et du CRIANN.Reuillon, R., Leclaire, M., and Rey-Coyrehourcq, S. (2013). Openmole, a workflow engine specifically tailored for the distributed exploration of simulation models. Future Generation Computer Systems, 29(8):1981â1990