Reliable ABC model choice via random forests

Approximate Bayesian computation (ABC) methods provide an elaborate approach to Bayesian inference on complex models, including model choice. Both theoretical arguments and simulation experiments indicate, however, that model posterior probabilities may be poorly evaluated by standard ABC techniques. We propose a novel approach based on a machine learning tool named random forests to conduct selection among the highly complex models covered by ABC algorithms. We thus modify the way Bayesian model selection is both understood and operated, in that we rephrase the inferential goal as a classification problem, first predicting the model that best fits the data with random forests and postponing the approximation of the posterior probability of the predicted MAP for a second stage also relying on random forests. Compared with earlier implementations of ABC model choice, the ABC random forest approach offers several potential improvements: (i) it often has a larger discriminative power among the competing models, (ii) it is more robust against the number and choice of statistics summarizing the data, (iii) the computing effort is drastically reduced (with a gain in computation efficiency of at least fifty), and (iv) it includes an approximation of the posterior probability of the selected model. The call to random forests will undoubtedly extend the range of size of datasets and complexity of models that ABC can handle. We illustrate the power of this novel methodology by analyzing controlled experiments as well as genuine population genetics datasets. The proposed methodologies are implemented in the R package abcrf available on the CRAN.Comment: 39 pages, 15 figures, 6 table

Les Associations polyspécifiques chez les Cercopithecidae du Gabon

International audienceIn North East Gabon, certain species of Cercopithecidoe are more often found in mixed troops than in monospecific bands. We have studied these interspecific associations in four diff erent regions: two tropical rain forest regions (of which one was periodically flooded) subject to low hunting pressures, and two degraded forests bordering native villages where intensive hunting took place. The results were analyzed statistically according to Fager's method (1957) which tests interspecific affinities. Cercopithecus cephus appears to be the species most often involved in associations (86.6 % of observed cases). In rain-forests, it associates mostly with C. nictitans, while in a degraded environment, it joins Miopithecus talapoin. This association tendency is also found in Cercocebus albigena, Cercopithecus nictitans and C. mona. Talapoins are found as often associated as alone. In our study area, C. neglectus was never observed in a mixed group. Different types of associations exist, ranging from a parallel existence of two (up to five) separate troops to a complete intermingling. In non-hunted zones, these associations are stable from one day to the next as well as over the years. Daily fluctuations occur however, most polyspecific troops being observed in the morning and evening. At nightfall monospecific bands tend to join and mingle with other species for the night. In degraded zones, the associations with the Talapoin scem to be a result of its "hunt-free" status. Native hunters do not hunt this monkey and therefore, any other "game" species associating with it benefit by its presence. Intraspecific agonistic behaviour appears to be absent even though the polyspecific groups share the same food habits (direct observation and stomach content analysis). It is this absence of competition, linked no doubt with the local abundance of available food, which probably makes these associations possible. An increase in troop size means a decrease in predator approaches going unnoticed and, consequently, the monkeys benefit from these associations. But this safety-in-numbers hypothesis may not explain satisfactorily the intraspecific association preferences which have been observed.Au N.-E. du Gabon, certaines espèces de Cercopithecidae se rencontrent plus souvent associées entre elles qu'en bandes mono-spécifiques. Nous avons étudié ces associations entre espèces dans 4 régions différentes : une région de forêt primaire et une de forêt primitive inondée, toutes deux constituant des zones peu chassées, et deux régions de forêt dégradée situées près des villages africains où la pression de chasse est intense. Les résultats ont été exploités statistiquement selon la méthode de Fager (1957), qui permet de tester l'affinité existant entre deux espèces. Cercopithecus cephus apparaît comme le singe le plus souvent associé (86,6 % des cas de rencontres) ; il s'associe principalement en forêt primaire avec C. nictitans et en milieu dégradé avec Miopithecus talapoin. La tendance à l'association se manifeste également chez Cercocebus albigena, Cercopithecus nictitans et C. mona. Le Talapoin se rencontre aussi souvent associé que seul. Quant à C. neglectus, il ne manifeste, dans nos régions, aucune tendance à s'associer avec d'autres espèces. Les associations sont de divers types, allant de la juxtaposition, de deux (et jusqu'à 5) bandes d'espèces différentes jusqu'à leur mélange complet. En zones non chassées, elles sont durables d'un jour à l'autre et également d'une année sur l'autre; elles montrent toutefois des variations au cours de la journée, le maximum de bandes mixtes se rencontrant le matin et le soir. Il semble qu'il y ait regroupement des espèces pour la nuit. En zone dégradée les associations avec le Talapoin apparaissent en partie comme une conséquence de la chasse, cette espèce n'étant pas considérée comme un gibier par les Africains et assurant ainsi une certaine protection aux espèces chassées qui s'associent avec elle. Les comportements agonistiques semblent absents entre les espèces différentes bien qu'elles exploitent apparemment le même milieu (observations directes et étude des contenus stomacaux). C'est cette absence de compétition, liée sans doute à l'abondance de nourriture dans ce milieu, qui rend possible ces associations. Les animaux en retirent une sécurité plus grande, l'augmentation du nombre d'individus permettant un repérage meilleur des dangers éventuels. Mais cette notion de sécurité n'est pas suffisante pour expliquer les préférences entre espèces que l'on observe dans ces associations

Continental collision, gravity spreading, and kinematics of Aegea and Anatolia

International audienceWe have carried out experiments using a layered medium of sand and silicone to investigate the lateral extrusion of a material which spreads over its own weight while being compressed by the advance of a rigid indenter. Boundary conditions in the box mimic those prevailing in the Anatolian-Aegean system. Both shortening in front of the rigid piston, which models the northward motion of Arabia, and extension resulting from the gravity spreading of the sand-silicone layer are necessary to initiate the lateral extrusion. Strike-slip faults accommodate the lateral escape and link the normal faults accompanying gravity spreading with the thrust faults in front of the rigid indenter. Strike-slip faults begin to accommodate extrusion at a late stage in the experiments after the normal and thrust faults have developed. Experiments also show that the initial geometry of the boundary of the spreading layer may result in the formation of two arcs behind which material extends, in a manner analogous to the Hellenic and Cypriot arcs, without invoking a rheological change at the junction of the two arcs. The experiments also suggest that southward motion of the eastern part of the spreading region is compensated by the northward advance of the piston, which is a possible explanation for the slower movement of the Cypriot arc compared to the Aegean arc

Organisation spatio-temporelle des activites individuelles et sociales dans une troupe de Cercopithecus cephus

A monospecific troop of Cercopithecus cephus was followed for five months using the radio-tracking method. Temporal and spatial distribution of the activities is described. Two peaks of locomotion are found in the first half of the morning and the second half of the afternoon. Phytophagy follows the same rhythm, while feeding on prey and resting increase at mid-day. Strong daily variations are shown in forest type usage according to the activity p erformed. The more open and tallest forest is chosen during the night and for fruit gathering, while the densest and lowest one is significantly preferred for resting. Parallel daily variations are found in the forest level usage : resting, insect hunting and social interactions occur at levels lower than locomotion and fruit gathering. The total time spent feeding does not differ between the age classes, however the time spent feeding on insects decreases with age while phytophagy increases. The young are found at significantly lower levels than the adults. The adult male stays higher than the other troop members, especially when resting. Inter-individual distances are lowest between females and young, while the adult male has a more peripheral position. Troop cohesion is higher at the end of the day. Physiological, behavioral and environmental constraints which might influence such activity rythm and differences between age classes are discusse

Polychronous mode automata

International audienceAmong related synchronous programming principles, the model of computation of the Polychrony workbench stands out by its capability to give high-level description of systems where each component owns a local activation clock (such as, typically,distributed real-time systems or systems on a chip). In order to bring the modeling capability of Polychrony to the context of a model-driven engineering toolset for embedded system design, we define a diagramic notation composed of mode automata and data-flow equations on top of the multi-clocked synchronous model of computation supported by the Polychrony workbench. We demonstrate the agility of this paradigm by considering the example of an integrated modular avionics application. Our presentation features the formalization and use of model transformation techniques of the GME environment to embed the extension of Polychrony's meta-model with mode automata

Relationships of Cardiorespiratory Fitness with Metabolic Risk Factors, Inflammation, and Liver Transaminases in Overweight Youths

The aim of this study was to assess the relationships of fatness and fitness with metabolic risk factors, including liver transaminases and inflammation in obese youth, taking in account gender, age, and pubertal stage. 241 children were studied (135 girls), age 11.9 ± 2.2 years (x ± SD), Body Mass Index z score 5.4 ± 2.7. For girls, VO2max was significantly associated with insulin (P = .001), Insulin resistance (HOMA-IR) (P = .005), and ALT (P = .012); a relationship was displayed between fibrinogen and age and % fat mass (FM) (P = .008); for boys, relationships were found between VO2max and diastolic blood pressure and triglycerides; independent associations were also found between age and insulin, HOMA-IR and HDL cholesterol; fibrinogen and sedimentation rate were related (P ≤ .004) with %FM. Their relationships are observed from young age and increase with the continuous increase of factors. This supports the need to treat overweight as soon as it is detected; improving CRF is one of the ways which could be used to prevent the complications of obesity

Modular interpretation of heterogeneous modeling diagrams into synchronous equations using static single assignment

The ANR project SPACIFY develops a domain-specific programming environment, Synoptic, to engineer embedded software for space applications. Synoptic is an Eclipse-based modeling environment which supports all aspects of aerospace software design. As such, it is a domain-specific environment consisting of heterogeneous modeling and programming principles defined in collaboration with the industrial partners and end users of the project : imperative synchronous programs, data-flow diagrams, mode automata, blocks, components, scheduling, mapping and timing. This article focuses on the essence and distinctive features of its behavioral or programming aspects : actions, flows and automata, for which we use the code generation infrastructure of the synchronous modeling environment SME. It introduces an efficient method for transforming a hierarchy of blocks consisting of actions (sequential Esterel-like programs), data-flow diagrams (to connect and time modules) and mode automata (to schedule or mode blocks) into a set of synchronous equations. This transformation minimizes the needed state variables and block synchronizations. It consists of an inductive static-single assignment transformation algorithm across a hierarchy of blocks that produces synchronous equations. The impact of this new transformation technique is twofold. With regards to code generation objectives, it minimizes the needed resynchronization of each block in the system with respects to its parents, potentially gaining substantial performance from way less synchronizations. With regards to verification requirements, it minimizes the number of state variables across a hierarchy of automata and hence maximizes model checking performances

Forces Generated by the Free Fall of DEMICHAIN

The free fall of an array of heavy chains (360 kg/sq m) generates extensive pressure in the depth of the ground. These pressures have been measured and compared to the threshold pressures that trigger anti-personnel landmines. When dropped from moderate heights (1 m), chains can generate enough pressure to set off active landmines buried 20 cm, provided that the area of their pressure plates is larger than a few square centimeters

Modeling and identification of passenger car dynamics using robotics formalism

International audienceThis paper deals with the problem of dynamicmodeling and identification of passenger cars. It presents a new method that is based on robotics techniques for modeling and description of tree-structured multibody systems. This method enables us to systematically obtain the dynamic identification model, which is linear with respect to the dynamic parameters. The estimation of the parameters is carried out using a weighted least squares method. The identification is tested using vehicle dynamics simulation software used by the car manufacturer PSA Peugeot-Citroën in order to define a set of trajectories with good excitation properties and to determine the number of degrees of freedom of the model. The method has then been used to estimate the dynamic parameters of an experimental Peugeot 406, which is equipped with different position, velocity, and force sensors