Efficient Implicit Parallel Patterns for Geographic Information System

International audienceWith the data growth, the need to parallelize treatments become crucial in numerous domains. But for non-specialists it is still difficult to tackle parallelism technicalities as data distribution, communications or load balancing. For the geoscience domain we propose a solution based on implicit parallel patterns. These patterns are abstract models for a class of algorithms which can be customized and automatically transformed in a parallel execution. In this paper, we describe a pattern for stencil computation and a novel pattern dealing with computation following a pre-defined order. They are particularly used in geosciences and we illustrate them with the flow direction and the flow accumulation computations

An Hierarchical Labeling Technique for Interactive Computation of Watersheds

International audience—The watershed computation is a prevalent task in the geographical information systems. It is used, among other purposes, to forecast the pollutant concentration and its impact on the water quality. The algorithm to compute the watershed can be hard to parallelize and with the increasingly data growth, the need for parallel computation increases. In this paper we propose a new method to parallelize the watershed computation. Our algorithm is decomposed into two tasks, the parallel watershed segmentation into a hierarchy that allows in a second task to retrieve randomly large watersheds at run-time in interactive time

ExaViz: a Flexible Framework to Analyse, Steer and Interact with Molecular Dynamics Simulations

International audienceThe amount of data generated by molecular dynamics simulations of large molecular assemblies and the sheer size and complexity of the systems studied call for new ways to analyse, steer and interact with such calculations. Traditionally, the analysis is performed off-line once the huge amount of simulation results have been saved to disks, thereby stressing the supercomputer I/O systems, and making it increasingly difficult to handle post-processing and analysis from the scientist's office. The ExaViz framework is an alternative approach developed to couple the simulation with analysis tools to process the data as close as possible to their source of creation, saving a reduced, more manageable and pre-processed data set to disk. ExaViz supports a large variety of analysis and steering scenarios. Our framework can be used for live sessions (simulations short enough to be fully followed by the user) as well as batch sessions (long time batch executions). During interactive sessions, at run time, the user can display plots from analysis, visualise the molecular system and steer the simulation with a haptic device. We also emphasise how a Cave-like immersive environment could be used to leverage such simulations, offering a large display surface to view and intuitively navigate the molecular system

Conditional Directed Narrowing

. We present an implementation of directed narrowing extended to the conditional framework, which is complete for two classes of conditional term rewrite systems : confluent and decreasing on one hand, level-confluent and terminating on the other hand. 1 Introduction Narrowing was originally introduced for solving unification of terms modulo a theory represented by a term rewrite system (E-unification). Next it has been used as the operational semantics of functional logic programming languages (see [5] for a recent survey). In this framework, the program is often represented by a set of equational Horn clauses, i.e. a conditional term rewrite system (CTRS). However, conditional narrowing is inefficient for practical applications because the search space is huge and contains infinite branches. This is why many authors have proposed optimizations to the narrowing procedure : innermost, basic innermost, LSE, lazy, approximations, etc.... Many of them need some restrictions on the re..

Un modèle pour la composition d'applications de visualisation et d'interaction continue avec des simulations scientifiques

La simulation informatique est un outil incontournable dans les sciences expérimentales. La puissance de calcul croissante des ordinateurs associée au parallélisme et aux avancées dans la modélisation mathématique des phénomènes physiques permet de réaliser virtuellement des expériences de plus en plus complexes. De plus, l'émergence de la programmation GPU a considérablement accru la qualité et la rapidité de l'affichage. Ceci a permis de démocratiser la visualisation sous forme graphique des résultats de simulation. La visualisation scientifique peut être passive : l'utilisateur peut suivre l'évolution de la simulation ou bien observer ses résultats après que le calcul soit terminé. Elle peut aussi être interactive lorsque le chercheur peut agir sur la simulation alors qu'elle se déroule. Créer de telles applications complexes n'est cependant pas à la portée de tout scientifique non informaticien. La programmation par composants est, depuis des années, mise en avant comme une solution à ce problème. Elle consiste à construire des applications en interconnectant des programmes exécutant des tâches élémentaires. Ce mémoire présente un modèle de composants et une méthode de composition d'applications de visualisation scientifique interactive. Elle s'intéresse, en particulier, à la conciliation de deux contraintes majeures dans la coordination de ces applications : la performance et la cohérence.Computer simulation is an essential tool in experimental sciences. The increasing computing power, parallelism and the advances in the mathematical modeling of physical phenomena allow to virtually run always more complex experiments. In addition, the rise of GPU programming has greatly increased the quality and performance of display. This has allowed to spread the graphical visualization of simulation results. Scientific visualization can be passive: the user can only follow the simulation's progress or observe its results when it is done. It can also be interactive in which case the researcher can act on the simulation while it is running. Creating such complex applications can, however, be tedious for non-computer-scientists. Component-based development is, for years, highlighted as a solution to this problem. It consists in building applications by interconnecting small programs completing elementary tasks. This thesis presents a component model and a method for composing interactive scientific visualization applications. It particularly focuses on the balance between two major constraints of these applications: performance and coherence.ORLEANS-SCD-Bib. electronique (452349901) / SudocSudocFranceF

On Partial Validation of Logic Programs

International audienc

A General Framework for R-Unification Problems

International audienc

The SIPSim implicit parallelism model and the SkelGIS library

International audienceScientific simulations give rise to complex codes where data size and computation time become very important issues, and sometimes a scientific barrier. Thus, parallelization of scientific simulations becomes a significant work. Many time and human efforts are deployed to produce efficient parallel programs. But still, many simulations could not be parallelized because of lack of time to learn parallel programming or lack of human resources. Therefore, aiding parallelization through abstracted parallelism or implicit parallelism has become a main topic in computer science. Many implicit parallelism solutions have been proposed such as algorithmic skeletons libraries, domain-specific languages or specific libraries. In this paper is introduced a new type of solution to give a totally transparent access to parallel programming for non-computer scientists of the domain of numerical simulations. This solution is an implicit parallelism model, called Structured Implicit Parallelism on scientific Simulations (SIPSim). After a description of the SIPSim model, this paper presents the implementation of the model, as a C++ templated library called SkelGIS, for two different cases of simulations: simulations on Cartesian meshes and simulations of two physical phenomena linked througha network. For each case, the implementation of the SIPSim components are described, and a simple simulation example is given. SkelGIS is then evaluated on two real cases, one for each case, first on the resolution of shallow water equations and second on an arterial blood flow simulation. To clearly state on SkelGIS performance and its ease of programming, different experiments on both cases are evaluated

Solving Disequations modulo some Class of Rewrite Systems

. This paper gives a procedure for solving disequations modulo equational theories, and to decide existence of solutions. For this, we assume that the equational theory is specified by a confluent and constructor-based rewrite system, and that four additional restrictions are satisfied. The procedure represents the possibly infinite set of solutions thanks to a grammar, and decides existence of solutions thanks to an emptiness test. As a consequence, checking whether a linear equality is an inductive theorem is decidable, if assuming moreover sufficient completeness. 1 Introduction The problem that consists in solving symbolic equations modulo a theory is called equational unification. A lot of work has already studied this subject in a theoretical way to know when the problem can be decided, as well as in a practical way to find efficient algorithms that solve the problem. Another interesting problem consists in solving the negation of equations, called disequations, i.e. in finding ..

E-Unification by Means of Tree Tuple Synchronized Grammars

: The goal of this paper is both to give a E-unification procedure that always terminates, and to decide unifiability. For this, we assume that the equational theory is specified by a confluent and constructor-based rewrite system, and that four additional restrictions are satisfied. We give a procedure that represents the (possibly infinite) set of solutions thanks to a tree tuple synchronized grammar, and that can decide unifiability thanks to an emptiness test. Moreover we show that if only three of the four additional restrictions are satisfied then unifiability is undecidable. 1 Introduction First order E-unification [29] is a tool that plays an important role in automated deduction, in particular in functional logic programming and for solving symbolic constraints (see [4] for an extensive survey of the area). It consists in finding instances to variables that make two terms equal modulo an equational theory given by a set of equalities, i.e. it amounts to solve an equation (ca..